 |
Podcast TranscriptThe Naked Scientists: Science Radio & Science Podcasts |
Superhero 3D X-ray vision
|
Novel HIV Vaccine Target Discovered
US Scientists working on HIV have uncovered a viral Achilles heel that might aid in the develop of a vaccine.
Writing in Science, Scripps Institute researcher Dennis Burton and his colleagues have been combing through more than 1800 blood samples from patients in Australia, Africa, Asia, Europe and the US looking for signs of antibodies, termed broadly neutralising antibodies, that can inactivate HIV.
'By first finding antibodies that can inactivate HIV, we can then work out which part of the virus they're targeting and then use that very component as a vaccine,' Burton explains.
Previous attempts to carry out this line of investigation have yielded only antibodies that target relatively inaccessible components of the virus, making it very difficult to incorporate them into a vaccine. But now, with new technology and an updated approach, the team have immediately struck gold with their first patient and uncovered two new antibodies, dubbed PG9 and PG16, which can block the virus from invading and infecting cells.
By making mutant viruses with slightly differing surface structures and testing the newly-discovred antibodies against them, the team have also worked out that PG9 and PG16 target the spike proteins (gp120 and gp41) that decorate the surfaces of HIV particles. The virus uses these spikes like molecular velcro to enable it to recognise and infect immune cells, a process that the antibodies can disrupt.
'Critically,' says Burton, 'the region recognised by these new antibodies is potentially a much more accessible site for vaccine design.' But if people who are infected with HIV are alreading making these antibodies, why are they still carrying the disease?
'Preventing infection in the first place is a very different challenge than ridding the body of established HIV, which integrates itself into the human host's DNA, making it much harder for the immune system to detect. The fact that patients can make these sorts of antibodies - and we got this result from just the first patient we studied - is really encouraging because it suggests that a vaccine should be able to do the same.
So, in someone who is not infected, these sorts of antibodies [produced by a vaccine] should be protective.' The next step will be for the team to continue to use their 'brute force' screening-based approach, now that they know it works, to track down more neutralising antibodies, and the viral sites they recognise, to produce a vaccine that can protect against the widest range of HIV strains.
6th Sep 2009
Steel Velcro
Velcro - or hook loop fasteners, are increadibly useful things. They were inspired by a natural means of distributing seeds such as burrs and have been used for uses varying from holding pockets closed to stopping things floating away in space. However velcro is normally made of plastic so is of limited use in hot conditions, and it has a limited strength.
A group lead by Josef Mair at the Technical University in Munich has developed something rather tougher, steel velcro. Using 0.2mm steel sheets and a carefully designed process of pressing and bending, they've formed something which works just like velcro.
They have a couple of versions - one called Flamingo, which involves holes in one half and sprung prongs on the other half. You push the prongs through the holes and they lock together. They also have the more traditional Entenkopf (duck head) which has groups of steel loops close to each other on one side and barbed prongs on the other, which will catch on the loops.
The velcro can carry up to 7 tonnes per square metre if the weight is pulling the sheets apart and up to 35 tonnes per square metre if it pulls along its length, so it's strong stuff. The real advantage is that it will maintain this hold at temperatures up to 800C so it could be used in assembling cars and other machines more quickly and easily.
References | |||||
| - The Metaklett Website | |||||
6th Sep 2009
Where did all the farmers come from?
Farming and cities seem very much the norm now but in the grand scheme they’re actually very recent developments. Modern humans have been around for about 200,000 years and farming has only been with us for the last ten thousand. Farming is a key threshold in human development because once you start farming a piece of land you can support a much greater number of people in a certain area than you would with most hunting and gathering. Although, there are some places in the world where land and sea are so abundant in food you don’t need to farm to support lots of people (but that’s another story…).
The Near East (that includes Iraq, Iran and Syria) is one place where farming is thought to have originated and later spread through Europe. And there’s been something of an argument between academics as to how the spread took place and how it happened so quickly. Some people have argued that farming techniques were rather peacefully communicated through neighbouring populations and that hunter-gatherers gradually gave up their lifestyle and language in favour of the farmers’. But some people argue that the farmers were a specific group of people who out-competed and eventually replaced the native hunter-gatherers in Europe.
Now Barbara Bramanti and her team have taken mitchondrial DNA (mtDNA) samples from three groups. Publishing in the journal Science this week,they took mtDNA from a group of 11,000 year-old hunter-gatherers and mtDNA from some of the earliest farmers. What they found was that these two groups were too distinct to be related. So they then looked at how ancient hunter-gatherers might be related to modern-day Europeans and again, the relationship was almost non-existent.
But it does seem that Central Europeans are descended, at least in part, from these early farmers. So what we can draw from this is that at the end of the last ice age, some people developed farming and they moved most the way across Europe, quite likely displacing the hunter-gatherers. And they think these farmers originated in an area around modern day Slovakia or Hungary but the researchers say they need to do a few more DNA studies to be sure.
So understanding when and why we started farming can tell us something about how we came to live in the cities we do today and also how farming might affect communities across the world which do practise hunter-gatherer lifestyles, e.g. the San in Namibia or Aeta in the Philippines.
References | |||||
| - Ancient DNA from the First European Farmers in 7500-Year-Old Neolithic Sites Wolfgang Haak, Peter Forster, Barbara Bramanti, Shuichi Matsumura, Guido Brandt, Marc Tänzer, Richard Villems, Colin Renfrew, Detlef Gronenborn, Kurt Werner Alt, and Joachim Burger (11 November 2005) Science 310 (5750), 1016. [DOI: 10.1126/science.1118725] | |||||
6th Sep 2009
Electricians shocked to find out how DNA repairs itself
Scientists in America have shown that cells send electrical signals along their DNA to check its integrity.
If mutations or damage to DNA goes uncorrected, especially if it affects certain critical genes, the results can be disasterous for the viability of cells or whole organisms since one consequence of DNA damage is cancer. Thankfully cells are equipped with enzymes that can recognise genetic spelling mistakes made by mutations and can excise the incorrect letter and replace it with the right one.
But a key question is how this checking process can take place quickly enough, given that the average human cell contains more than 3 billion genetic letters - that's more than a pile of encylopaedias piled taller than a person. To find out, Caltech scientist Jacky Barton and her colleagues used E. coli bacteria to study the process.
E. coli double their numbers every 20 minutes so they also need rapid mechanisms to check their DNA sequence and they also contain the bacterial equivalents of many of the same DNA repair enzymes used in humans, making them ideal study subjects. The researchers focused on two enzymes in particular MutY and EndoIII, which are charged with identifying specific types of DNA damage. These proteins can walk along a DNA chain, checking the sequence, but there aren't very many of them (there may be only 30 MutY proteins in an entire cell) and they move much too slowly to completely screen the genome within the time that they do. But what the researchers also noticed is that these proteins carry with them clusters of iron and sulphur atoms (4Fe-4S), which can pick up and release electrons, changing their charge in the process.
Now, in an elegant series of experiments in which the team made specific molecular tweaks to the structures of some of these repair enzymes, the researchers have shown that the repair enzymes work in pairs and signal to each other using the DNA between them like a telephone line. The process is incredibly simple: one repair protein lands on the DNA and activates itself. A second repair protein lands further along the DNA chain and releases a small amount of electric charge, which is conveyed along the DNA chain as if it were a wire. If it reaches the first protein this indicates that the DNA region separating the two proteins is intact and the sequence is correct. The first protein picks up the electrical charge and detaches from the DNA before binding somewhere else.
But if the sequence is wrong, as a consequence of mutation or damage for example, the signal does not transmit and the two proteins remain attached to the DNA and work their way slowly towards each other, laboriously checking each genetic letter as they go. When a fault is discovered and repaired, signalling between the two proteins is restored and they can depart to screen other parts of the genome. In this way, using electrical signalling, the entire genome can be checked and maintained in tiptop condition by using just a small number of repair enzymes.
6th Sep 2009
Pagerank for Species
Most conservation effort seems to be put into species which are pretty or otherwise attractive to humans, but often there is no point in trying to conserve them if their ecosystem collapses. For example there is no point in stopping anyone killing pandas if the bamboo they live on dies out. In simple cases this result is obvious but in most ecosystems a species depends on, and is dependent upon, many other species. This makes it very hard to predict the knock on effects of loosing a species, without using huge complex computer models.
According to Stefano Allesina and collegues Google's pagerank might hold the answer. This is the ranking system that Google uses to help decide which order to return search results. Basically if a site has lots of other sites linking to it, especially if they are important, then it is probably important too and should appear at the top of the list.
Stefano has been applying this to food webs, so if lions, hyenas, leopards etc all eat a type of gazelle, they will all transfer some of their importance to the gazelle, depending on how much of their diet is gazelle. The gazelle, in turn, transfers importance to the grasses which it eats.
They then used these relationships to rank the species by how much damage they would do if they went extinct, and compared it to other much more complex mathematical models, and found that the results were the same. The Page Rank system is obviously scalable to immensely complex systems - it works for the web, so Stefano's system should work on a food web as complex as they come in the real world, and help conservationists concentrate on the most important species to protect.
References | |||||
| - Article in PLOS computational biology | |||||
6th Sep 2009
How Many Licks...?
Aaron Santos, University of MichiganChris - Now, have you ever wondered how many babies are getting born everyday or how many solar panels it might take to power the UK? Well, one man has not only answered these questions but he’s also gone on to show us how we can work it out for ourselves. He’s written a book and it’s called “How many Licks” and it’s been published and it’s come out this week in the US. It comes out here in the UK very shortly and his name is Aaron Santos and he’s a mathematician & physicist of the University of Michigan. Hello, Aaron.
Aaron - Hi. How are you?
Chris - Very well. Thank you. Good to have you with us on The Naked Scientists. So first of all, before we come onto “How Many Licks” and perhaps why it’s called that, tell us a bit about yourself and what do you do?
Aaron - Well, I’m a postdoctoral researcher in the Chemical Engineering Department at the University of Michigan and my background is in physics which is basically where I learned to do all these sort of problems, these sort of calculation problems.
Chris - What sort of physics are you doing?
Aaron - I do mostly statistical physics. So, a lot of the things with nano scale systems, a lot of different self-assembly systems and nano particles, and a little bit of biology, but much more just regular straightforward chemistry.
Chris - And so, what led you to come out of the physics world and say, “Right. Let’s write a book in which we try and look at some of these complicated calculations about the world around us.”
Aaron:: Well it was actually, it was in the middle of my graduate class when I was studying for them and there’s a problem that was on the class that was basically, how do you – you have to calculate something that you have no idea how to calculate it first and it’s a general problem first originally proposed by Enrico Fermi, and I think the problem he originally used was something like how many piano tuners are in Chicago and this was something that his students were expected to answer by just doing straightforward calculations. So, it just seemed like it would be a good idea to just put a clutch of these problems into a book for math.
Chris - And the name “How Many Licks,” how did that come about?
Aaron - Well, there was a commercial. I’m not sure if in the U.K., you guys get Tootsie Roll pops, but it’s basically a Tootsie Roll encompassed in a lolly pop and there was a pretty famous commercial back in the ‘80s about – there was this owl when the cape goes up and he asked the owl, how many licks does it take to get to the Tootsie Roll center of a tootsie pop and the owl basically just takes a bite out of it and says three. So, this was kind of the real answer to that question because that’s one of the things what we consider in the book. How many licks would it really take if you were actually going to sit down there and do it?
Chris - Well, one of the other things you’ve been considering is say, the question, you sometimes see TV adverts where they use scalability and lots of small increments of something, adding up something very big. One of the examples you give in your book is how many ants would you need in order to carry humans. So talk us through that one.
Aaron - Yeah. That’s one of the simpler problems in the book. So, it’s commonly said that an ant can carry 50 times its own weight and if that’s true, how many would you need to actually pick up a human being and just kind of use it to walk you around? Well, ants come in a lot of different sizes. If you look on, I think it’s Wikipedia, I think there’s a factor of 500 between the smallest ant and the largest ant weight.
Chris - I wouldn’t like to guess what the factor is for humans, probably depending on some countries is quite big.
Aaron - Yeah. One would imagine, those countries probably should remain nameless.
Chris - I think our country is between the two of them, probably leading the way actually! So go on. How do we calculate this then?
Aaron - So, if you look at the ants, the ones that are crawling around my apartment, they’re about 20 milligrams in mass and if they can carry 50 times their own weight then that means that they can each carry a gram. So, a normal human being is somewhere around 65 kilograms. If I divide 65 kilograms by 1 gram, then you can calculate pretty simply that it’s about 65,000 ants that you need to pick up one human being.
Chris - Do you think it’s reasonable?
Aaron - I never get into whether things are reasonable or not in the book. I mean, there’s a lot of things to consider. First of all, how are you going to fit that many ants underneath you? You either need very large shoes or you need to be lying on your back and then there is some question, whether or not you could even fit that many ants. So, I try to avoid any pretense of reality in any of these calculations. It’s not really what we’re going for here.
Chris - Now, I got sent an email the other day, Aaron, where someone – it said on there – it said that, “Don’t scroll down until you’ve read the top line” and then it said, “Around the world, about 35 million people are having sex at this precise moment.” And it said “Now scroll down, now scroll down, it set apart from one old timer who’s currently reading his emails.” So, how many people are currently engaging in sexual congress right now then and how would you calculate something like that?
Aaron - I should say before I answer this one that I answered a similar question in a talk that I gave once. And was heckled mercilessly by a woman in a crowd who was convinced that the percentage of time that I thought people were actually having sex was much too low. So, you might get a few angry calls in from this but…
Chris - We won’t judge it by your own standards Aaron. It’s all right.
Aaron - Okay. So to do a problem like that, you’d want to say, “Alright, well how often does a normal person have sex and this clearly depends on what type of person you are.” If you’re a priest, it’s going to be much rarer than if you were in a committed relationship in your early 20s. But the number I used to calculate this one, it was, I’d say once every three weeks seemed like a reasonable number. You’re certainly not going to be having sex once every day, at least not by my lifestyle. And once a year seems much too long, so once a week seems like a good compromise. And then you say well alright, how long does a typical sexual encounter last and then it depends on do you count foreplay, do you count what counts as a sexual encounter. But I thought, 15 minutes seems like a reasonable amount of time for that. So, that gives you…
Chris - People here in the studio are nodding. They think that’s okay.
Aaron - Okay good, good. Although I have to say that the people that I have generally asked these questions to tend to be scientists, so I think my results might be a little skewed, but you guys fit that demographic. So, maybe that’s why you guys are nodding in agreement. But that would be 15 minutes out of three weeks, so you could calculate that that’s about 0.05% of the time and then if that percentage also applies to the number of people that are having sex, then it’s just 0.05% of the population which would be about 3.3 million people.
Chris - So also my estimate was far too high. My email that I got then was ten-fold too high probably.
Aaron - It could be or I could have messed up on one of the numbers that I gave you, but I would question the email more than the numbers because I at least know where those are coming from.
Chris - But the point of all this is that it’s basically showing people how you break down a big complicated problem which scientists frequently encounter into a series of small steps and make a few small assumptions in each step in order to arrive at a ball park sort of figure.
Aaron - Exactly. I mean, you want to start with the things that you know how to do first. I mean, you don’t want to just guess at the number of people having sex because you could be way off with that. But if you start doing things that you are familiar with and then just multiplying them together then usually, you can come up with something that’s pretty close.
September 2009
The Centre of the Cell
Professor Fran Balkwill of Queen Mary’s University, London; Fiona Haddesly Smith & Esmee, Petchley Academy; Helen Skelton, Blue Peter.Meera - This week saw the launch of the Centre of the Cell, a new children orientated science center located in the heart of Tower Hamlets and I’m inside the center itself now and it’s very impressive, structurally, because it’s basically a large orange pod that suspended from the ceiling over a working laboratory. And with me now is the director of the project, Professor Fran Balkwill from Queen Mary University of London. So Fran, tell me more about The Centre of the Cell. What exactly is it and what does it hope to achieve?
Fran - The Centre of the Cell is about inspiring the next generation of scientists and doctors and it’s also a unique project, not only because of its location within the working research building, but because it’s actually scientists who have led the project and its content has come from over 80 of our scientists.
Meera - And what is the content really? So, what do scientists come up for it?
Fran - The top-level message is that your body is made of millions of tiny cells. When you’re real, your cells have gone wrong and scientists in this building and all around the world are trying to find ways to make cells right again and make you better.
Meera - And what would you say the aims of the centre are because it’s located here in Tower Hamlets which is not necessarily most affluent of areas. So, that’s one of the primary goals of it, isn’t it?
Fran - Yeah. It’s about raising educational social aspirations. It’s about saying to the kids at Tower Hamlets, “You're worth it.” It’s very much a local project. We’ve involved 8,000 local children so far in evaluating every stage of the project but it’s also got a global reach because we have our website which has had over 10 million hits from 140 different countries and many of the games in the pod are also available on the website. But it is, in terms of the pod itself, it’s about bringing in our local young people and inspiring them about science and having a dialogue with them.
Meera - And what would a stereotypical visit then involve?
Fran - It’s free. Booking is made online because it’s a sort of planetarium type of experience. As children come in, they look down over the research laboratories and they come into the pod. Then there’s an opening audiovisual sequence which is about cells and cell biology and then in the middle of the pod, the lighting changes and this amazing structure called the nucleus opens and inside, you find games about cells and cell biologies.
Meera - Now, I’m just wondering around inside the Centre of the Cell and the pod has opened up to a variety of interactive games and I’m here with Esmee from the Petchley Academy. Hello, Esmee..
Esmee - Hello.
Meera - Are you normally interested in science at school or has this helped you to learn?
Esmee - I like science but I prefer more practical science and it helps me learn it. So, I think this is helpful. I mean, it’s really interesting, the way it’s actually in a laboratory and you can watch real scientists work. It kind of puts into perspective.
Meera - So we’ve heard the aims of the centre and the opinion of a student visiting it. But is it really educating visitors? Well, Fiona Haddesly-Smith is the Vice Principal of the Petchley Academy. So Fiona, what do you think about the center?
Fiona - I think the most significant thing will be that it is such an interactive set of games that are going on here. And it is very, very interactive, and everything that the students have been learning in the classroom, they can actually take out of the classroom actually use it and see it working in practice. Especially when the students are seeing the scientists working downstairs, so they do realize that scientists have real jobs and it’s not just something that me as a teacher teaches in the classroom.
Meera - And would you say then that the games and activities here really do then match what they’re doing in their classrooms, so they match the curriculum?
Fiona - They certainly do match the curriculum and I’ve been looking around and it is absolutely fascinating to see that a lot of the challenges that are presented at Key Stage 3 and actually Key Stage 4 are very precisely addressed here, especially modern science, modern treatments of medicine. Looking at cancer, looking at the way in genes are inherited, looking at the way in which genetical traits are passed on from one generation to the next. And it’s really fantastic to see that you’re talking now to a real life scientist who is saying the gene for deafness is passed on from one generation to the next. And although I may be teaching that in the classroom, they can actually see it working in action here and that is absolutely brilliant.
Meera - Today’s launch was opened by Blue Peter presenter to Helen Skelton. Hello, Helen.
Helen - Hello.
Diana - So Helen, what’s your opinion on the Centre of the Cell here?
Helen - Well, I was invited to come along and to be honest when I walked in, I just kind of stood there and I was going, “Wow! This is cool.” I have to hold my hands and to be honest, if you said to me, “Helen, let’s go and look at a science lab,” I’d think, “Hmm. I’d rather not. That sounds a bit boring.” But this is isn’t like that. It’s full of games, it’s full of actual human organs that you can get your nose right up to and I think it just brings it to life and for me, science was always the boring subject at school, but this certainly isn’t a boring experience.
Meera - What do you think about the fact that it’s hanging, kind of over the labs here at St Barts, do you think that helps the people to see what scientists do?
Helen - Yeah, I definitely do because I think it’s easy to go to a museum and you're sort of distant from things then. But actually, what you’re looking at is happening right beneath you. And sadly, everybody can relate to cancer or HIV or whatever it is and the fact that there are people working right beneath their feet to combat those things is really quite remarkable.
References | |||||
| - The Centre of the Cell | |||||
September 2009
|
Does Shaving make hair grow faster?All of my life, I have heard it said that shaving makes hair grow back faster and that once you start shaving, you’re then committed for life. What’s the answer? John Kemp |
|
Diana - Well, the short answer is no. We had a really good answer from the forum about this actually from databit who said that hair grows actually in a cone shape. So, when you let it grow naturally, the end looks thinner and therefore, the hair looks thinner. But when you actually shave it, you cut it right at the base where it’s at it’s very thickest and that makes it look much thicker. So, once you’ve start shaving your hair, the stubble will look much thicker and make it look like more like it’s actually growing, but there isn’t. It’s the same. Chris - And the other point I think also to make is that when you’re cutting a hair that is growing already, it’s got a head start because it’s already an actively growing hair compared with a hair follicle that was not active because hair follicles go through various cycles of activity and inactivity. So therefore, you’re cutting a growing hair already therefore, it’s already growing. Therefore, it’s going to grow back quicker. Diana - That’s right. You sort of bring all the hairs back down to the same level of growth and so, it appears as if they’re all sort of growing at once. |
|
September 2009 |
|
john Kemp asked the Naked Scientists:
All of my life I have heart it said that by shaving it makes hair grow back faster, and that once one starts shaving they must continue to for ever more. Is there any truth to this? If so what is the science between the rate of growth and shaving one's hair?
John
What do you think?
- john Kemp - 20th Jul 09
There is no truth to that; shaving or cutting hair does not change the rate at which it grows. Some people also believe that it causes hair to gro back thicker, but that isn't true either. - exton - 20th Jul 09
I think that it's a story put about by Mums who don't want their little boys to grow up! I think it could be true, however, that the first hairs (bum fluff) that you get on your chin may be less visible when they are allowed to grow compared with cut-off ones because they taper to a point. Women have a similar problem with their legs. - lyner - 20th Jul 09
Oh jeez, I was fooled by my own mother! - Chemistry4me - 21st Jul 09
On many other occasions as well, I'm sure.
- lyner - 21st Jul 09
She once told me that eating tofu would make my skin whiter. I believed her.
- Chemistry4me - 22nd Jul 09
Mine told me that "only common people" eat in the street!!!!! Hang on - this is general nonsense not General Science! - lyner - 22nd Jul 09
Yes it does... That's why it is not advisable for a woman to shave their legs or lips... They will end up with more hairs - wanhafizi - 23rd Jul 09
Is there actual evidence?
- lyner - 23rd Jul 09
There is no truth to that; shaving or cutting hair does not change the rate at which it grows. I believed my frens :) - dionne12 - 23rd Jul 09
This is a common myth that has a small teensy bit of truth to it.
See the whole discussion | Make a commentWhen you shave, you are not removing the hair, you are shortening it to skin level. Compared to growing a new hair, your cut hair has a head start: 1. It is an active follicle 2. It already has some hair grown, just you cannot see it below the surface of the skin. There is also the myth that your hair grows back thicker after being shaved. There is also a small amount of truth to this as well. When a hair grows in, it is not a cylinder. It is in fact an elongated cone. The tip of a new hair comes to a point and as it grows it gets thicker until it reaches its full thickness. When you cut the hair off at the skin, you have cut it off at its full thickness. Now when it starts to grow in, it will be full thickness to begin with. It will not be any thicker than before, but it will already be at full thickness. This is also why hair stubble is very stiff when compared to new or longer hair. The short hair being already at maximum thickness is a lot stiffer. Fresh hairs are still very thin and bend easily. - Databit - 23rd Jul 09
| |
|
Can you run faster on the moon?My son Joshua and I were wondering if Usain Bolt was to go sprinting on the moon, he’s the guy who’s this amazing athlete from the Caribbean who seems to be able to run faster than anyone else ever thought was possible. If he was to go sprinting on the moon but without being hindered by extra weight like space suits and equipment and so on, would he run faster or slower than on earth? I believe gravity is a bit weaker, but I’m not sure if that would be a benefit for locomotion or not? Barry Rawlins |
|
Dave - On the moon, the gravity is about a sixth of the earth so you can jump much, much higher. Whether this helps you with running, it depends on what kind of running you’re doing, I think. If you’re trying to sprint, if the sixth amount of gravity then you’re going to have a sixth of the amount of friction between your feet and the floor because friction basically goes at how hard you’re pushing against the floor, and this means – but your mass is still the same, so you still need the same force to accelerate. So, he’ll be able to accelerate about a sixth of the rate as he could do normally. So, in a 100-meter sprint, he’s almost certainly going to be a lot slower. But if you’re running a very long way, you could probably get an advantage because you can take huge strides. So, you can sort of – you could take a huge stride and then not do anything for a three or four seconds while you fly through the air and then you can land and do a little bit of exercise and fly through the air for a bit. So, you get some time to recover in between so I think you could probably run long distances faster, but short distance is not maybe as quickly. Diana - So, it’d be like the laziest race ever then, wouldn’t it basically? Dave - Oh, it depends how fast you’re going but, yeah. |
|
September 2009 |
|
Rawlins, Barry G asked the Naked Scientists:
Dear Chris and team,
My son and I were wondering: if Usain Bolt could sprint on the moon, without being hindered by extra weight - space suit or breathing equipment - would he run faster or slower than on earth?
I believe gravity is weaker, but we're not sure if this is a benefit for locomotion?
Many thanks, Barry and Joshua
Nottingham, UK
What do you think?
- Rawlins, Barry G - 6th Sep 09
Our limbs ( or those of champion sprinters) are fairly optimal for Earth conditions. I think the problems of matching our limbs to the Moon gravity could limit top speed. Both acceleration (traction) and top speed would be affected. You would need to lean much further forward to keep from rotating backwards (something we do automatically down here) if you want good acceleration. This would be difficult or even impossible. As for speed; you would be effectively in a lower 'gear' than optimal. I think that, with suitable extensions, like the 'blades' used by Paralympic runners, it would be possible to run much faster. Each stride could be much longer as the time off the ground would / could be at least twice that on Earth. I think that's what the good old equations of motion imply. Contact with the ground slows you up so less contact would mean faster. There would be a long learning time involved and you'd have to clear it with the record keepers. - lyner - 6th Sep 09
In theory, if the legs have to support less weight then they should be able to put more effort into moving. In practice though, traction might be a problem. I also recently heard someone talking on the radio about whether it is possible to bring the sprint times down much further because as the speed increases the runner spends less time with their feet in contact with the ground: to go faster you need to apply more force to the ground but as you go faster you have less time to do so. We also need to remember that it's not just a case of strength either; power-lifters have immensely strong legs but don't make good sprinters because they can't move their legs quickly enough, so a sprinters leg muscles not only need to deliver the necessary force but do so quickly.
- LeeE - 6th Sep 09
I agree with both the above. The astronauts who landed on the moon had a different way of moving which was a kind of skip. They also had a huge amount of mass (at least it would have weighed a lot on earth) on their backs and were in cumbersome space suits. They found this to be a better way of getting about. It was also important that they didn't lose their balance because getting up with the suits they had on would have been difficult. In theory you should be able to go faster on the moon. I guess long running spikes might aid traction. One problem would be that the stride length would be large; it is likely that the fastest pace would involve lengthy periods off the ground on each stride. A problem would be maintaining your orientation accurately and consistently enough so that you didn't end up in an untidy heap on the surface after a few paces. It may even be worth a runner carrying a sizeable gyroscope to retain orientation. It makes me think that a two wheel bike with bulbous, spiked tyres would be a useful vehicle. Do you think I should patent it. Oh blow, I've just disclosed it. Well nobody else can patent it now then. - graham.d - 7th Sep 09
There is a limiting speed corresponding to how fast you can move your leg backwards. I don't think it is all that fast - as people trying to jump/run off an old Routemaster Bus in motion or trying to run downhill will find.
See the whole discussion | Make a comment- lyner - 8th Sep 09
| |
|
What is Limonene?I was wondering what limonene is and what it’s used for? Don, Norwich |
|
Chris - Brilliant. Yeah, well limonene, it’s the stuff that makes oranges and lemons smell orangey and lemony. So, if you take an orange and you scrape the peel a little bit and smell your fingers, it’s that very intense orangey citrus smell, isn’t there? Don - Yeah. Chris - And that is the limonene. The orange peel contains huge amounts of it. It’s a very big organic molecule. It’s lots of carbon and hydrogen atoms stuck together in giant ring structures. And in fact, we did an experiment on The Naked Scientists a little while back. Dave did it as a Kitchen Science where you actually blasted some of the limonene through a candle by squeezing the peel of the fruit and you spurted the limonene into the flame. Dave - That’s right. You produce a sort of aerosol of limonene into the flame and limonene is really flammable and so, it catches fire. Chris - But the reason that fruit makes it is because it’s also quite nasty for things other than humans who haven’t got fingers to peel an orange. If you try to borough through the peel of an orange, you’d have to eat the peel and the peel doesn’t taste too good. Limonene is mildly toxic and being organic and unpleasantly tasting as it is, it puts off insects and that’s a way that the tree uses of keeping its fruit in good condition. Don - Okay. I find it also in my shower gel. Why is it in there? Chris - Sure. Well the answer is rather than trying to invent artificial flavours and colourings and things which would do the same job as a molecule which is already doing the job very well in nature, sometimes it’s easier just to use the natural product and then you can also have a marketing benefit because you can say, “Hey! This is a natural product. It’s got limonene in it.” So, rather than having to use orange flavored stuff or a small molecule that smells the same, then you can just use the natural product and then you get two bangs for your buck. So, what it’s doing in your shampoo is contributing a nice orangey aroma and which also, because it’s fatty and oily, it will stick to your skin quite well. It won’t get washed off by the water and it leaves you smelling vaguely with a faint aroma of oranges. Have you noticed that? Don - Yeah. I have. Chris - Then we’ve got the answer right. Thank you very much, Don. |
|
September 2009 |
|
|
Why can light not escape a black hole?If a difference between a star and a black hole is density of matter (black hole being a collapsed star) then why cannot light escape the gravity of a black hole but it can escape a gravity of a star? To my understanding: 1)When a star collapses it does not gain mass, it only becomes denser, 2)Gravity depends on mass, not density. Indrek Torilo |
|
Chris - The point he’s making is that a black hole is a collapsed star. So, all the mass of the star ends up in the black hole. So, if light can come out of the star in the first place, given that there’s no more mass now in the black hole when it’s collapsed, what’s changed that now light can’t get out? Dave - That’s right. When you take a star and convert it into black hole, you actually normally lose an awful of mass. It involves all sorts of explosions and lots of energy given off so that black hole normally weighs an awful less than the original star did, but that mass is much, much closer together - it’s much more dense. The force of gravity even the Newtonian force of gravity is essentially proportional to the inverse square. So, if you’re twice as far away from it, the force gets four times weaker. So, if you take a star and squash all that mass very close together and then you stand on the surface of it, apart from being burned up and everything, you stand on the surface of it then you’re going to be a lot closer, a lot more mass. So the gravity is going to be much, much stronger. And once you go into relativity and general relativity then that mass can bend space enough that light always gets bent around and it can never escape at all, ever. Chris - So, if the black hole blew up again and you took the same mass and put it back to something that was the original size of the star – so in other words, the density was low again then it would start to emit light again. Dave - Yeah then light could escape no problem. |
|
September 2009 |
|
Indrek Torilo asked the Naked Scientists:
Hi Naked Scientists,
I love your show and I have downloaded and listened to all the podcasts on your site back-to-back while I drive. Truly awesome!
Anyways, I have a question now.
If a difference between a star and a black hole is density of matter (black hole being a collapsed star) then why cannot light escape the gravity of a black hole but it can escape a gravity of a star? To my understanding:
1)when a star collapses it does not gain mass, it only becomes denser,
2)gravity depends on mass, not density.
Kind regards,
Ints, from NSW, Australia
What do you think?
- Indrek Torilo - 6th Sep 09
Have a look at my comment in this thread regarding the effect of density and gravitational force: http://www.thenakedscientists.com/forum/index.php?topic=25411.0 - LeeE - 6th Sep 09
First you need to understand where gravity comes from. It is the magic force that pulls every atom of matter towards every other atom of matter. Because nearly all the matter on planet Earth is beneath our feet, gravity pulls us down to the ground. But to answer your question there’s 3 other things you need to know about gravity: 1) Gravity is very weak, although it may not seem like it when you fall off your bike. If you pick up a mug of coffee you have beaten gravity, since gravity wants to hold the mug to the table. If you pick up a paperclip with the weakest toy magnet from a Christmas cracker that magnet has beaten all the gravity in all the world. 2) Gravity fades quickly with distance. When you are standing, the ground just beneath your feet is very close to you and pulls quite hard. But there isn’t much of it. Most of the rest of the world is also pulling you down but it’s miles away. On the other side of the world Australia is massive and is also pulling you down but it is nearly 8,000 miles away and only pulls you very weakly. Because gravity is pulling at different rates from different places scientists like to average out the gravity to a place they call the Centre of Gravity. On Earth the Centre of Gravity is at the centre of the planet. Some gravity is closer. Some is further. Some stronger, some weaker. But it all averages out at about the centre. 3) Gravity is cumulative. One atom of matter has a tiny, tiny amount of gravity but all the atoms of the world have enough gravity to hold us to the ground. Now.... say you are in an airplane going on your holidays. You can walk up and down in the plane and gravity is more or less normal. But imagine that while you’re flying some aliens come along and squash the planet Earth down to the size of a beach ball. So far as gravity in the plane goes you shouldn’t feel any difference. The World still has the same amount of atoms in it so it still has the same amount of gravity – it’s just all squashed into a really small size. And its Centre of Gravity is in the same place because the top of the planet has been squashed down and the bottom has been squashed up so everything still averages out at it’s centre. But if you parachute down to ground things would be very different. Balancing on a planet Earth the size of a beach ball, now all the matter in the world is within two feet of you and will all be pulling on you really strongly. You’ve got all the gravity of the world concentrated into a small ball and, as a result, it would squash you flat! So as you squeeze a planet smaller it still has the same amount of gravity over all but it is now concentrated into a smaler space, so it feels stronger if you get right up next to it. If you squeezed the Earth even further, until it has a radius of about 12mm (or about an inch across) something strange would happen. Now all the matter of the World is squashed soooo close together and it’s gravity is soooo concentrated that gravity within the Earth becomes stronger than all the forces which normally push atoms apart and the world would start to squash itself down even more on it’s own. This size is indicated by what's known as the Schwarzschild Radius and if you squash any object down enough eventually you will reach it’s Schwarzschild Radius, and it will continue to collapse on it’s own. This is how Black Holes are made. So as a star collapses it's gravity becomes more concentrated so it collapses further still. Most physicists believe that it will therefore keep on collapsing indefinitely, becoming infinitely small. The gravity as you get up really close to it will therefore increase indefinitely and so it’s gravity will become infinitely large at its infinitely small surface. There will therefore be a region around it where even light will not escape and this is called it’s ‘Event Horizon’. The event horizon therefore indicates a region where the escape velocity needed to escape the gravity of the object is greater than the speed of light. It does not indicate the actual size of the black hole which is, as I said before, infinitely small. If our Sun suddenly collapsed into a black hole it would not affect the orbit of the planets in our solar system because it’s overall gravity would not be affected. Incidentally, some ‘light’ can escape a black hole and is known as Hawkin Radiation, which can cause a black hole to slowly ‘evaporate’. This is my understanding of the relationship between black holes, gravity and light. I am not a physicist and I am sure other members will find some holes in my explanation. But I believe it is broadly speaking correct. - John Chapman - 7th Sep 09
A simple to use calculator is available here to show the characteristics of blackholes http://xaonon.dyndns.org/hawking/ - syhprum - 7th Sep 09
JC That long post of yours (above) has confused me. Is the "gravity" to which you refer 'gravitational force', 'gravitational field', 'gravitational potential' or just plain mass? Why not use the conventional terms in an explanation? It would make it far easier to follow and to comment and to see whether your model is an improvement on the existing one. - lyner - 8th Sep 09
Ooh. Shiny. - jpetruccelli - 8th Sep 09
Hi SC I don't bleedin know. What do you think this is, a science forum? Well, it was supposed to be a layman's explanation, although it probably reveals the entire extent of my knowledge about black holes. I'm not sure that I appreciate the difference between the three but 'gravity is weak' refers to what I might call it's force, 'gravity fades' I suppose refers to it's field and 'gravity being cumulative' could be gravitational force or potential. I don't really know. The explanation is one that was used in a science fiction book I once read who's two main characters were a physicist and a black hole! The novel was written for a general readership, although the author did have a PhD in physics. It made good sense to me at the time although the book probably did a much better job of explaining it than me. I jumped in with a rushed answer before one of you experts could write a technical post. I hoped my explanation was a good approximation of the principles involved. Is there anything wrong with it? Please try and keep your reply not too technical. Ta. - John Chapman - 8th Sep 09
JC Your numbered points 1,2,3 are spot on. I think that, when you use the word gravity, you are really talking about the force that something with mass produces on something else with mass - that is really the gravitational field (at least the field is the force on one kg ). When you're talking of the gravity getting more concentrated it's really the mass that is getting more concentrated. When you are below the surface of the Earth, for instance, all the 'shells' outside you produce a zero field - pulling in different directions and actually cancelling out. So you experience less and less weight force as you go down because its only the bits underneath that are attracting you. (Always, as you say, effectively towards the Centre of Mass). IF, however, you are dealing with a dense object like a black hole (or your golf ball sized Earth), the Mass is so concentrated that you can get a lot nearer the CM before you are inside any 'shell'. So the gravity field gets higher and higher (the so-called inverse square law: halve the distance and you get four times the field). At any given large distance, you couldn't tell the difference, though. For any massive object to become a BH, its Mass needs to be concentrated into within the Swartzchild radius which 'that link' will calculate for you. I don't think it's nitpicking to draw the distinction between the Mass and its effect. It helps in the end. - lyner - 9th Sep 09
Thank you SC. Your comments are always appreciated and, when I understand them, highly educational! - John Chapman - 10th Sep 09
Here is a question; How close would a 96 ton object have to be to a 234 ton objest in space before their gravitational fields pull them together. - G-man - 12th Sep 09
If they are stationary and free floating, surely any distance. As far as I know, although gravity weakens quickly with distance, it never actually disappears. This is what leads some astrophysicists to believe that the whole universe will eventually come crashing in on itself in a 'Big Crunch' (although I believe that the velocity with which the universe is expanding following the Big Bang and the amount of dark matter in the universe has lead many physicists to accept that the Big Crunch will never happens and we will keep expanding indefinately until the whole universe becomes cold and dark). By the way, welcome to the site, G-man. - John Chapman - 12th Sep 09
HI; and thanks for the welcome! I just read that the Commander of the spaceshudle had to fire the thrusters to close the last two cm's to the spacestation. - G-man - 12th Sep 09
My opinion :) think of it as a question of distance. When you look at earth as you stand on it you will feel one G, right? At least I know I do so. (or more lately due to unforeseen circumstances (obesity:) Only Joking.. ) But if you went to Earths exact 'middle' all those 'gravitational forces' would equal each other out. That means that in the middle of the earth if it kept its size as usual you weight 'nothing' at all. Consider now shrinking Earth to somewhere around five to two cm (sorry don't remember the exact measurement/circumference there) What you do then is to break a limit for how much mass inside a certain radius that is allowed to interact (two way communication) within our universe. If we leave the hypothetical discussion of what Hawking radiation might be out of this for the moment you have now succeeded in creating a Black Hole from our poor Earth. If you were left where you were standing before the Earth shrunk you would still feel that one G. If you on the other tentacle followed its downsizing :) you would now be ripped to smithereens by its 'tidal forces' as its same 'total invariant mass' now would occupy such a small place in SpaceTime. It's like all particles have a gravitational 'influence' on everything else and when you change their density and compresses it under the ‘Schwarzchild radius’ that a Black hole demands (defined as that ‘radius for a given mass where, if that mass could be compressed to fit within that radius, no force could stop it from continuing to collapse’ into a zero size hole which then would be the beginning of a new Black Hole) Then the mass becomes 'infinite' and your black hole will be there. In fact it seems to be a balance between mass and distance that will create a black hole. Another example of this principle is " The Planck length is related to Planck energy by the uncertainty principle. At this scale, the concepts of size and distance break down, as quantum indeterminacy becomes virtually absolute. Because the Compton wavelength is roughly equal to the Schwarzschild radius of a black hole at the Planck scale, a photon with sufficient energy to probe this realm would yield no information whatsoever. Any photon energetic enough to precisely measure a Planck-sized object could actually create a particle of that dimension, but it would be massive enough to immediately become a black hole (a.k.a Planck particle), thus completely distorting that region of space, and swallowing the photon. " In this case we are discussing 'energy' instead of 'invariant mass' but the energy needed for the transformation to happen would, as I understand it, need to be already 'infinite' for it to 'transform'. One of the criteria people use for defining a Black Hole is that light will have no way out from its EV (event horizon)and only 'travel' in one direction, to its core. You can see Black Holes as 'mathematical infinities' and, just as those, coming in different sizes. Thats why I speak about distance versus mass as defining when it happens. It's a strange concept I agree. As for if 'pure energy/radiation' could transform into a Black Hole inside SpaceTime I believe that idea to be a violation of the idea that 'invariant mass' accelerating never can become a Black Hole, no matter its velocity, as long as light can be sent out from it. And a singularity differs from a star in that, as its mass becomes 'infinite' its size will also 'disappear' into infinities becoming impossible to define, as I have understood it. For us that means that a black holes mass might be 'size less' even though the space surrounding it will 'expand' as seen from a observer inside the EV. - yor_on - 4th Oct 09
Mass is inversely related to density. \rho= M/V where V is for volume and M is for mass, and \rho makes density. Imagine we could tamper with the sun. Imagine we decided to expand the sun a million times; we might end up with what could be described as a thick gas of particles, whose gravitational pull was less than that of the compactified sun we began with. Now imagine we decided to add the mass of a million averagelike stars together with our sun, but not expanding the struture of the sun, we would be trying to squeeze matter into the free spaces - this high density means an increase of gravtational pull. The more mass you add to a given space in he vacuum increases the gravitational influence of the object in question. Remember, mass (and thus gravity) is inversely related to te density of a system. - Mr. Scientist - 4th Oct 09
Why are my lines scored out above lol?
- Mr. Scientist - 4th Oct 09
If you try to model this action with maths and take relativity phenomena into account you will find that it can not happen. Acceleration contains time as a member. Gravity affects time. So gravity affects gravity and is therefore self limiting. It can not progress to a singularity. - Vern - 4th Oct 09
You probably clicked the strike through button. It is just to the right of the underline button which is to the right of the italics button which is to the right of the bold button. It is just above the smiley button. - Vern - 4th Oct 09
Oh :)
- Mr. Scientist - 5th Oct 09
Nice explanation Vern, please include me as a member of the 'no singularity club'
- syhprum - 5th Oct 09
I'm not the originator of the notion; I came across a study by a group of university students who were trying to model Black Hole creation; they decided that it was not possible. Now I can't find the reference. - Vern - 5th Oct 09
You know, M-Theory, last time i read can actually rid quantum theory of singular regions in space and time. - Mr. Scientist - 5th Oct 09
| |
|
Can Refrigerators be made more efficient to actually generate electricity? |
|
Peter - Hello. Well, my question is fairly complicated, so you have to bear with me a little bit. We start off with the refrigerator. Now, the refrigerator, actually, you get more benefits than the energy you put in. In the sense that you put a certain amount of electricity and to move heat from the hot to the cold or pump heat away from the cold areas. And you can pump significantly more heat in the energy you put in. So, you got sort of reverse efficiency where you can move several times and probably, I don’t know three or four times. I don’t know the exact figures. The energy reacted in… Dave - That depends on the temperature you’ve – the difference in temperature which the fridge is working across. Peter - Yeah, so you’re actually moving physically more heat than the energy you’re putting in. Now given that, can’t we do the same thing in reverse and use the fact that we’ve created a heat differential to power a heat engine to generate the electricity back again. And now, one or two things will happen. Either will get more electricity out than we should in a sense that we’ve got an efficiency which is greater than the factor… For an example, let me say, if we pump in four times as much heat and to convert the heat back to electricity, we need only 25% efficiency or better to actually win in the game. Chris - So, this is worth making tons of free electricity just by running your fridge for cooling your beer down, Dave. Dave - Okay, so basically you’re asking if a fridge can pump far more heat than the energy you put in, that’s definitely true. In fact, if it’s pumping for very small temperature difference it can pump 100 times more heat than the energy you put in. Can you make a heat - temperature difference with that and then use that temperature difference in order to generate electricity? We can use that temperature difference to generate electricity, we do use temperature differences to generate electricity all the time. Essentially by using a heat engine - something like a car engine is a heat engine. And basically they can produce high quality electrical energy by moving heat from a hot place to a cold place. But a fridge is essentially just a heat engine running backwards and again with a normal heat engine the amount of energy you can get out compared to amount of heat you can move is to do with the difference between the two temperatures. The bigger the difference in two temperatures, the more efficient it is. And so you’ll never, ever going to get more energy out by going around to the circle like this. Chris - You’ll just be violating the laws of physics basically, it’s just not going to happen. Dave - Yeah, there’s a really, really fundamental law of physics. Which essentially says you can’t generate useful energy from nothing and this would violate it completely… Chris - It’s an analogous question to, if I have a propeller on my car as I drove along, could I connect that to some kind of generator. And then power the car with the generator, it’s kind of getting a free lunch isn’t it? And it just doesn’t happen, energetically speaking it’s just not going to happen. Dave - Yeah, and I think actually with this one it would be far, far worse than, it would work far less well than that. |
|
September 2009 |
|
|
Why does tea taste nicer out of china cups?Why does tea taste nicer out of china cups, and coke taste better from a glass than a plastic cup? Ros, Peterborough |
|
Chris - I’d say, it’s the placebo effect, wouldn’t you? I think it’s just because you automatically think it’s nicer because it’s in glass. Diana - Yeah, having lived, sort of six years on and off as a student, I think it starts to taste the same after a while anyway. Dave - A lot of what you experience from a meal food is to do with the surroundings which is why restaurants spends so much money on having pretty stuff in the room not just on the food. |
|
September 2009 |
|
|
Can talking to plants make them grow faster?I've heard that talking positively to plants makes them grow better. Is there any good scientific evidence for or against that claim? Jesse, Ithaca |
|
Chris - The answer is probably not. But I did a bit of poking around, in fact we have covered a story on the Naked Scientists a couple of years ago by Scientists (the reference is Meh Jong Jong) who is a crop researcher over in South Korea. And published this in the journal of Molecular Breeding. So it’s a peer reviewed journal but I'm not sure how robust the science is. But what they did was to, for some reason - and they don’t say why in their paper, they were playing classical music to different plants. And they tried 14 different types of classical music to see what effect this would have on the plant growth. And the plants, not surprisingly, did not respond at all. So then they thought well perhaps it’s a mixture of tones and perhaps plants are sensitive to a range or specific set of tones. So then they started playing sounds at specific discrete frequencies at plants and monitoring gene expressions. So they would grind up the plant and see which genes have been turned off or turned on in response to the presentation of a tone over a period of time. When they played certain plants a tone at 50 Hz, a series of genes went down, turned off. When they played the same species of plants some sounds of 150 Hz, 125 Hz or 250 Hz, the same genes increase their activity. And when they use the molecular machinery, the bits of genetic sequence that turned those genes on and off and link them to another gene, that made the cells change colour, that’s called a “reporter gene” they could, by playing certain sounds to the plants, get these plants to change colour. Suggesting that plants are are sound sensitive, so maybe in the case of cereals we know they have ears, so maybe they are sensitive to sounds and therefore maybe, there is some validity in saying you should talk at them. I think it’s more likely though, that the CO2 that you are emitting in your breath when you talk to your plants is going to have a bigger effect than the range of frequencies. But maybe Bloke’s voices being more low frequency dominate it would have a better effect than women’s voices, I don’t know. Diana - So, Prince Charles was right then? Chris - Maybe Prince Charles is right, maybe. Dave - Are plants vibration sensitive? Because when wind blows past them they’ll vibrate, and if it’s windy then they’re going to want to have all sorts of different settings, than if it’s not.. Chris - Yeah, plants definitely response to being moved around. Because they realize that this is bending them and they therefore need to strengthen and so they deposit more growth related products and then they turn on growth related genes in the other side of the stem to the one in which they are bending. So they strength from the side that they are bending away from. So in other words, it makes it stiffer on that side. And that’s why trees can look a little bit bent but still stand up despite say an on shore breeze or something. So that’s why. |
|
September 2009 |
|
Jesse asked the Naked Scientists:
Dear Naked Scientists,
I love your show, and listen to it every week.
Here is a question: I've heard that talking positively to plants makes them grow better. Is there any good scientific evidence for or against that claim?
Thanks,
Jesse
Ithaca, NY, USA
What do you think?
- Jesse - 7th Aug 09
Breathing CO2 on a plant may have a small, small difference but what really happens is that people talking to their plants give them more care and attention generally.
- Make it Lady - 7th Aug 09
I suspect MIL is about right. I should think the only way to put it to the test, would be to treat 3 identical plants the same. Talk to one, shout and scream at another and ignore the last. I would think after a week or two you will get a result, that being, a visit from the men in white coats. - Don_1 - 7th Aug 09
Scientists have discovered some sound-sensitive genes in plants that, they suggest, can modulate gene expression in response to the presence of certain audio frequencies; suggests that wheat really does have "ears"! Actually I'm a little sceptical and I've not seen any follow up of the observation, so it might be just "noise" in the research field. (Sorry, terrible puns). http://www.thenakedscientists.com/HTML/content/news/news/833/ Chris - chris - 11th Aug 09
From an episode of mythbusters a while back, they played different types of music to plants. Their control tests grew at a normal rate, and those with additional noise grew faster. From memory, rock music was the most successful; I'm assuming this is because of an increase in the noise. Classical was the least successful of all the music.
- Laura_Kelly - 17th Aug 09
Actually, I stumbled upon this while trying to find sources for a lab report I'm writing. I just finished conducting an experiment like the one mentioned above. I bought 3 identical plant (well...as near as I could come to identical)and yelled and screamed at one, sang and spoke nicely to the other and ignored (aside from watering) the other. They all stayed in the same place except when they were getting their 'treatment' so that no other factor could come into play. Although I did feel crazy, the one that got yelled at kept wilting afterwards, even though it grew at a similar rate. All in all, the one we sang to did only slightly better. The one that grew the least was the one that got ignored...weird.
See the whole discussion | Make a comment- Lily - 4th Dec 10
| |
|
Why aren't planets compressed by gravity like stars are?As I understand it the nuclear fusion of stars stops gravity from compressing them until they cannot be compressed anymore because of the force of the neutrons repelling each other and when stars run out of fusible materials they are compressed to this point. What keeps the planets from being compressed by gravity as the stars are when they run out of fusible materials? Stephanie |
|
Dave - Well, yeah. Star, it’s not actually the fusion which is holding the stars up directly. It’s actually their temperature. If you had a gas, the hotter it is the more pressure it will exert, the harder it would push out. So stars are basically supported, they’re basically made out of very, very hot gas - plasma that are supported by their temperature. So if a star gets hotter it will expand, star cools down it will shrink. A planet doesn’t have to be supported like that, planets are made out of solid, lumps of things they’re basically supported by the repulsion between atoms and molecules, in the same way as the table is supported or you’re supported. So they are not big enough for the need the temperature to support them and basically just molecules and atoms are strong enough. Chris - Because planets like Jupiter are just around the threshold of what we call brown dwarfs, aren’t they, they’re failed stars are not quite big enough to squeeze themselves enough to trigger a fusion to actually get going. Dave - Yes, small stars it can also be supported just by this molecular strength basically. |
|
September 2009 |
|
Stephanie asked the Naked Scientists:
As I understand it the nuclear fusion of stars stops gravity from compressing them until they cannot be compressed anymore because of the force of the neutrons repelling each other; when stars run out of fusible materials they are compressed to this point.
So what keeps the planets from being compressed by gravity as the stars are when they run out of fusible materials?
What do you think?
- Stephanie - 6th Sep 09
A planet's mass is much lower than a star's mass.
- lightarrow - 6th Sep 09
. . . . . so the internal gravitational attraction is not enough to cause crushing. The atoms are strong enough to withstand the force in planets. (added for clarity, lightarrow - OK?) - lyner - 6th Sep 09
Ok. I was lazy, didn't want to add anything else
- lightarrow - 6th Sep 09
But, for some stars, humangeous super nova explosion compress the centre of the star... ...i think... - wanhafizi - 7th Sep 09
The radiation implosion of a super-nova that results in a black hole isn't really too different from the radiation implosion that is used to start the fusion process in fission-fusion and fission-fusion-fission bombs.
See the whole discussion | Make a commentI believe that much of the initial mass of a pre-super-nova star is blown away by the explosion and the mass of the resulting neutron star or BH is far less than the star's original mass i.e. although our sun could form a BH if it were 1.4 times larger, the resulting BH would have less than 1.4 solar masses. Not sure about this though, off hand. - LeeE - 7th Sep 09
| |
|
Why is laundry lint always blue?Why is laundry lint always blue? Why is it that no matter what colour the laundry, I mean even white, the fluff that comes out of filter system at the other end, it’s always lilac, purple or grey in colour? Dolphin Burns |
|
Diana - That’s a good question actually. And now, Dr. Karl Kruszelnicki has worked a bit on on this and he actually did win an IgNobel Prize for his lint research. But he says that for both belly button fluff and laundry lint, is actually an average of all the colours of your clothes. So all the stuff that comes off even your white laundry, will end up being sort of slightly grayish, bluish, horrible colour. And if you think about even if you do have a lot of black clothing, and I'm sure most people will have at least one item of black clothing, will tend to sort of fade to grey and those are the bits that are more likely to disintegrate and fall off and become lint. Dave - It’s not always blue. I once washed a bathroom mat from the floor, which was already fluffy and bright red. And that shed completely, it jammed up the whole washing machine and the lint that came out of that was definitely red. Chris - And the other slights a bit of additional information or perhaps you might or might not wants to know about Dr. Karl’s study, he actually invited to send in their belly button fluff, to see that colour that was. I think it came out pretty much the same, didn’t it? Diana - Yeah, the IgNoble people told him to never, ever do research on this again. |
|
September 2009 |
|
- Dolphin-Byrnes - 6th Sep 09
- RD - 6th Sep 09
- glovesforfoxes - 6th Sep 09
- RD - 6th Sep 09
| |
|
How should or why should a polyester sheet make a fluorescent light bulb glow?How should or why should a polyester sheet make a fluorescent light bulb glow? I accidentally rubbed my pillowcase, which is 100% polyester against the mini-fluorescent bulb, which is in my bedside lamp. And it glowed for a split second, I repeated this numerous times and every time it worked as long as I touch the contacts. It’s just a simple lamp from Wal-Mart made in China. Am I being exposed to some kind of random chemical or radioactive toxin or something? Dane Buxbaum |
|
Dave - No, this is perfectly normal. In fact we did a Kitchen Science on this a couple of years back. Basically polyester is a polymer which is quite good at charging up. So if you rub that against your hair or against other sheets it would tend to, as it touches the sheets it would slowly get electrons transfer to it (or away from it, I’m not sure which way with polyester) and so it gained a charge. This means if you move it near a fluorescent tube, a fluorescent tube is basically hollow tube with some very low pressure mercury gas in it. Some of that mercury gas will be ionized, it would’ve lost electron, you move a charged thing near that some of those ions will move towards or away from the charged thing, will accelerate along, will hit other mercury atoms and knock electrons off those and then you’ll get a cascade effect. And get a little bit of electric current flowing through the tube one way, when you take it away then it will flow back again, and that will transfer energy to the mercury atoms some of that they will release as ultraviolet light. This will hit the sort of white coating inside of the tube and that will emit visible light, which you can see as this flash of light. Chris - So there’s nothing radioactive about your bed, it’s okay then, you’re okay. |
|
September 2009 |
|
BUXBAUM,DANE asked the Naked Scientists:
I accidentally rubbed my pillowcase (100% polyester) against the mini
fluorescent bulb in my bed side lamp and it glowed for just a split second. I repeated the phenomenon numerous times to even greater effect. It would not work with any other fabric I tried - nor the flesh of my hand. I should say that the lamp was turned off at the time. The bedspread set was purchased at Walmart and made in China.
Am I being exposed to some kind of chemical or radio active toxin??? What could have caused this?
What do you think?
- BUXBAUM,DANE - 3rd Feb 09
Static electricity anybody?
- Chemistry4me - 3rd Feb 09
Yes, it's static electricity. You can generate very high fields from static electricity (many kV) and these are enough to strike a fluorescent tube. If you take a traditional fluoescent tube and stand under a power line with the tube vertical, you can get it to strike easily. They won't glow very brightly because the current flow is low, but it can be surprisingly bright.
See the whole discussion | Make a commentNo worries, Dane. - graham.d - 4th Feb 09
| |
|
Why can we not gain immunity to the common cold? |
|
Chris - I wish I knew the answer to that. It’s actually just simple numbers. There are two reasons for this. One is to be immune to something, your immune system has to see it in the first place. So you have to be infected with the thing, so you then learn to neutralize it in the future. Now, that would be simple if there was one virus, but in fact there are hundreds. If you look at the rhinovirus family, which is the cause of the common cold, around most of the year, there is about a hundred of those. If you look at the enterovirus family, there’s about a hundred of those. There is 50 or 40 adenoviruses, many of which cause upper respiratory and eye infections. Then there are the corona viruses, the parainfluenza viruses, the influenza viruses and to add insult to injury, these viruses also mutate. So not only are there hundreds of them around for you to get your immune system’s head around but also they are moving target. They are changing their molecular appearance, so even if you have learned to recognize it, there’s no guarantee that you’ll recognize it again the next time. And given that there are all these hundreds of viruses and the average person gets about two or three colds per year, that’s three life times worth of cold infections before you’ve actually got any chance of being immune to all of them, by which time they probably have changed. So, I don’t think there’s really any prospect of ever being able to cure the common cold with the exception that what scientist including Steven Legit who is a researcher of University of Maryland had done, is they’ve sequenced genetically all of the rhinoviruses so far. And they know how they divide up to a little subfamilies and it might be that if you a made a vaccine based around some members of some of those subfamilies, then every time you immunize someone who gets one of the subfamilies you are protected against all the other members of that family. So you could make a vaccine but it would have probably be based around lots and lots a different members and probably be unfeasible. Who knows, let’s hope though that we come up with some kind of common cold cure soon because since you have children you’re into a whole different ball game. |
|
September 2009 |
|
foram joshi asked the Naked Scientists:
Dear Naked Scientists,
my question is: why do we catch colds so often? Why do we not become immune to diseases like the common cold?
What do you think?
- foram joshi - 18th Aug 09
We do gain immunity to the common cold, we never get the same cold twice!! However there are so many different strains of the common cold, each time we come into contact with a new strain, we have to go through the process of having the cold in order to gain the immunity!
- Variola - 18th Aug 09
Variola, the TNS 'Pox in Residence' has given the definitive answer. Google 'Common Cold Unit', I'm sure you will find plenty of info on this government sponsored research unit, which was abandoned with total failure. - Don_1 - 18th Aug 09
I have never had the common cold OR the flu in my entire life. I start to believe I have a natural immunity against rhinoviruses and Infuenza. I do have a strange case of asthma like auto-immune bronchial disorder. Strange in the sense of: it triggers when I don't get enough sleep for two-three days in a row, but I don't have any specific allergies and I'm not having episodes caused by the usual asthma inducing factors. Maybe these conditions are related, maybe not. But I'm pretty sure I'm not the only guy on the world with natural rhinovirus/Influenza immunity. - Nizzle - 18th Aug 09
Behold, the only man in the world not to have had 'man flu'! See I knew there had to be one!!! Every other man, they get a slight sniffle and they are convinced they need round the clock nursing!! - Variola - 18th Aug 09
If the deffinition of 'flu is " a cold, but so bad you can't get out of bed" then I have never had 'flu. Perhaps serological analysis would tell me something else. On the other hand, I generally get a cold or two each Winter- they just don't bother me much. I guess I just have a robust immune system. Anyway Is "Man 'flu" the opposite of Bird 'flu"? - Bored chemist - 18th Aug 09
Nope bird 'flu is actually real, and doesn't come as the result of a minor sniffle. - Variola - 18th Aug 09
That is actually a very interesting question you've got there foram joshi. Such a common illness and no vaccine? Well as already mentioned there are about a ton of different types of cold (To us, they all seem the same). The viruses causing colds are called rhinoviruses, and there are around 100 of them (Depends who you ask, i've seen the number vary between 98 and 103 rhinoviruses). Here is the deal, and actually the web is full of the news at the moment. Scientists have just managed to discover the genetic make-up of all the known Rhinoviruses! What they discovered was rather astonishing. They discovered that some of the genetic make-up is supposedly identical between all rhinoviruses, which actually will enable us to start thinking of how to produce the vaccines against cold. - DrChemistry - 18th Aug 09
HIPV's,enteroviruses,coronaviruses and adenoviruses also cause common colds too. Yep,I remember reading a journal article on it a short while back, I will see if i can find it again. - Variola - 18th Aug 09
Nope bird 'flu is actually real, and doesn't come as the result of a minor sniffle. I think I caught this, I opened the window and in flew enza. - Don_1 - 19th Aug 09
HIPV's,enteroviruses,coronaviruses and adenoviruses also cause common colds too. Yep,I remember reading a journal article on it a short while back, I will see if i can find it again. I take that back. Variola is right. Enteroviruses and Rhinoviruses are however from the same Family. The problem with using general terms are that we forget to mention sub-divisions. So some of the other viruses that were mentioned can cause cold symptoms, but also other symptoms not related with colds. It all depends on small differences. Putting that aside, the main message was that a vaccine against rhinoviruses (Unable to find anything about the discovery of the genetic make-up of the other viruses), is on its way. - DrChemistry - 19th Aug 09
And let's not forget that virus genomes mutate, so a vaccin has to be reinvented everytime a virus reinvents itself (as long as the mutation occurs in membrane component coding genes)
- Nizzle - 19th Aug 09
When the vaccine is rendered useless depends entirely on how it was constructed and what genes that mutate. If 75% of the genetic make-up is the same for all rhinoviruses, I wouldnt worry about inefficient vaccines just yet. If it does go and get nasty, I see no problem in reinventing the vaccine. Those who wish to stay away from colds probably wont mind either.
- DrChemistry - 19th Aug 09
Sorry I was just being pedantic. As regards to vaccines, a vaccine against rhinovirus would not work against an enterovirus despite them being from the same genus. ( I think!) As Nizzle pointed out, if the genetic similarity involves the ENV part of the genome then we could be in luck. However given the large size of rhinovirus family shows the variation, I think it will be difficult to construct a vaccine that will be affective against 75% of them. And then there are all the inherent problems that trying a new vaccines has surrounding it. Mind you, it does give some scope for using rhinovirus in gene therapy. - Variola - 19th Aug 09
I dont think a Rhinovirus vaccine would work against enteroviruses either I do not think that is likely at all, but well, I could be wrong. Once again its all in the details Do you mean it will be difficult to contruct a vaccine affective against 75% of all rhinoviruses, or it will be difficult to construct a vaccine that will make affective use of the 75% similarity in all the rhinoviruses? Sorry, didn't quite get that no matter how many times I read it. Might be my poor level of english gramma - DrChemistry - 19th Aug 09
Well I typed it with confidence, but then had a moment of not being so sure! Without looking at the genome both I wasn't so confident! But I am reasonably sure it wouldn't work. No it is my poor quality of typing! I was thinking over the problem while typing, and it came out confused! I meant that given that 75% of the genome is the same, but also given that the rhinovirus family is so large,it would be difficult to develop a vaccine against all of them. We show no immunity from other rhinoviruses no matter how many we have.i.e if we have 10 different rhinovirus infections, we can still get the other 90 or so that are left. (in theory). That shows just how diverse the rhinovirus family is. It's not as straightforward as developing one against a 4 or 5 strain genus, although that's not simple in itself. I am also not sure there will be much finding put into finding a vaccine because colds, although a nuisance are rarely life threatening. - Variola - 19th Aug 09
I'm not that well informed in the area of genetics, but to me it sounds a bit like a fairytale if we could kill enteroviruses with a rhinovirus vaccine. I have seen no such predictions wirtten anywhere, at all. I just wanted to make sure I understood it correctly. Would be horrific If I replied on an idea I had misunderstood I myself would probably not take a vaccine against colds. There are better ways to get rid of it than taking a bunch of chemicals, so for me it does not matter if the vaccine is against 1 type of rhinovirus, or all 100 of them. P.s. Allegdly scientists believed they could make one vaccine against the majority of them because of the way the Rhinoviruses were built up. I have to admit though that I read it as a very not-well developed extract, so I am more than willing to take your point of view. - DrChemistry - 20th Aug 09
Is it an evolutionary thing? We don't die of colds and they don't seriously affect our reproducing capability so we only need to 'tolerate' them. As in lots of parasite - host relationships there is a certain amount of tolerance and a certain amount of co operation between the two. The rhinovirus may have been protecting us from other things in our system and we never knew it. The fact that people have spent decades rushing to the Doctor at the first sign of a cold (and expecting to be given something for it) has probably meant that antibiotics have been used far more than they should have been. An early night and a lemsip / whisky / whatever you fancy is usually the best way to deal with and to get resistant to things like a cold. - lyner - 24th Aug 09
Chris should be answering this really, as he is the forum expert of immunology. It is evolution in one sense, our beautifully clever immune system has developed and adapted alongside viruses such as rhinovirus, hence why it is so well honed to prevent us suffering the ill-effects of pathogens. It is more than just WBCs mooching about in the blood system waiting to pounce, it is a whole complex system of communication. There has indeed been some speculation that the alleged 'junk' DNA found in our genome shares similarities with the genome of retroviruses, leading to the conclusion that somewhere along the evolutionary path,these 'alien' genes have transcribed into our development. However I don't consider it as an endosymbiotic relationship though, as if it was we would not have developed the targeted immune response to the rhinoviruses. Yes unfortunately medicine was so impressed with itself for creating antimicrobials, that we pressed ahead hailing them as wonder drugs. Science, in it's proud naivety didn't realise that something so tiny, it can only been seen with a microscope would manage to outwit and outdo them at every turn. Basically,relieving the symptoms and taking it easy on yourself is the only thing you can do, while your clever immune system dispatches the virus, while of course taking its name and number for future reference! Good nutrition is helpful too, nothing like a bunch of co-factors and prosthetic groups to keep the body happy! - Variola - 26th Aug 09
Thanks for the clear and comprehensive answers you all came up with for this question; I think I also gave a fairly thorough answer on the podcast, which you can access via the link above.
See the whole discussion | Make a commentChris - chris - 8th Sep 09
| |
|
Do plants have immunity?Do plants have immunity to viruses and bacteria? Mike, Oregon |
|
John Carr from the Department of Plant and Sciences at the University of Cambridge: John - Most microbes like bacteria, fungi, and viruses can’t infect the plant. But some through evolution, have gained the ability to break down the initial barriers to infection such as cell walls and so on and these can cause disease. Now in response the plants have evolved the ability to respond to and recognize particular types of pathogens. So, that’s why some plants have resistance genes and these is a sort of genetic mechanism of allowing them to pass on the ability to fight off particular diseases. Now when this occurs, you might find that the cells which are initially infected with a virus or a bacteria or fungus actually commit suicide. And this is one way of creating a kind of a scorch earth against the pathogen but also it’s a way of creating signals, lots more interesting chemicals that float out through the plant tissue. Sometimes plants will produce salicylic acid, it is the parent compound of aspirin and it is a very, very powerful inducer of resistance. So if plants are producing salicylic acid, they are better able to fight off perhaps the first pathogen to attack them unremarkably they’re able to fight off possibly lots of other types of pathogen as well. So salicylic acid itself aspirin like compound can give rise to something they call methyl salicylate and this can float off to other plants and influence other plants so they become more resistant. Jonathan Jones, Sainsbury Laboratory, Norwich: Jonathan - Hi, I am Jonathan Jones. I worked at Sainsbury Laboratory in Norwich. Humans have two kinds of immune system, they’ve got the innate immune system, which recognize molecules that pathogens can help making like flagellum of bacteria for example. And they’ve got the adaptive immune system which involves antibodies and that’s what is triggered when you immunize against viruses for example. Plants and many others sort of less sophisticated organisms have only an innate immune system. They can recognize molecules and pathogens and activate defense. The defense components involve making a sort of bleach - an active oxygen cocktail that inhibits microbes and can culminate in cell death. They also in plants make a lot of anti-microbial proteins that inhibit growth of microbes but also many pathogens squirt proteins into plants cells, to shut down that immune system. And then there’s another immune system involving proteins inside the plant cell that recognizes when these molecules show up inside the plant cell and activate defense. |
|
September 2009 |
|
Completely unqualified answer: Yes and no. Plants do have an immune system though not like our own and it is far from perfect so they do not have immunity to everything. A plant's immune system is usually one of two types: (for lack of enough knowledge, I am making these terms up) Defensive and non-reactive. Defenseive is slightly similar to our own immune system in that it destroys the infecting bacteria etc. but it generally does not do it in a targeted way like our immune system does. The plant's defenses are often a chemical or physical element that makes it hostile to the invading baddies. This is often accomplished by poisons. In a non-reactive immunity, a plant will prevent infection by not having the receptors or features that make it infectable. Many viruses, bacteria, and the like require specific receptors to bond to to infect the cells. By eliminating those or not having them in the first place, a plant can be immune to those specific baddies. - Databit - 4th Aug 09
The first line of defense that plants have against bacterial infection is performed by the stomata, the same structures on the leaf surface which are mostly associated with regulating gas exchanges between the plant and the atmosphere. Maeli Melotto, from the University of Texas at Arlington, studies how the stomata close when faced with a potential bacterial infection, and how bacteria counter that. I wrote about it for Pesquisa, a Brazilian magazine. It has been translated to English here: http://revistapesquisa.fapesp.br/?art=1850&bd=1&pg=1&lg=en. - mariaguimaraes - 5th Aug 09
Plants can also kill their cells by apoptosis - programmed cell death - so I suspect that they will use this as an anti-viral strategy - if cells surrounding a site of infection all self-destruct then there will be nowhere for the virus to replicate next...
- chris - 6th Aug 09
In humans, L-ascorbic acid seem to have antiviral properties (http://www.aids.org/atn/a-111-04.html or http://www.orthomolecular.org/resources/omns/v01n12.shtml). Although human and plant is nowhere near identical in terms immune systems, the Vitamin C in fruit plants may fight of infections. A second possibility (I could be wrong here). Plants are pleased with sunlight, however, intruding bacteria for instance might already be fought off the plants by the the small percentage of UVC rays thrown at it from the sun. - DrChemistry - 14th Aug 09
if that were true, then any microorganism exposed to the rays would die way earlier than reaching the plant. - glovesforfoxes - 14th Aug 09
if that were true, then any microorganism exposed to the rays would die way earlier than reaching the plant. A helping hand from the sun to our plants. Plants do not have an active defense system like human do and depend on other chemical or physical mechanisms to take place within or outside the plant, one probability could be apoptosis as Chris pointed out. Other ways of preventing bacterial or viral infections in plants could include the root net, or as I mentioned, the L-ascorbic acid in some fruit plants. The roots are in fact very complex structures. We have the primary root, lateral roots and the root hairs. Specifically 'trained' if you like, to absorb only what's needed for plant growth. Soil contain loads of bacteria, and hence plants had to find a way to keep them out. Bacteria is usually of a sizer bigger than what the roots can absorb, and are hence left out. However, if I remember right, I once read an article by Department of Agriculture in which they had supposedly spotted that some sort of bacterium had evolved shocking capabilities of getting absorbed by some specific roots. Whether this is the actual case I have never heard a conclusion on (surely something worth investigating). However, if this actually is the case, the bacteria or microorganism in question would not die prior entering the plant. Edit: Spelling mistakes, inaccuracies, punctuation etc. - DrChemistry - 14th Aug 09
isn't sap part of the immune system of a tree? Although this is not the case for all plants, most do not have sap.
- techmatt - 16th Aug 09
I have a distant memory of my A level biology teacher also mentioning that plants can also selectively block off some of their conducting vessels in order to prevent the spread of microorganisms via that route. The mechanism of blockage was the secretion of callose, a carbohydrate, into the phloem sieve plates. Chris - chris - 17th Aug 09
I was just wondering plant such as chili that produce capsaicin does that act as an defensive agent against bacterial as well?
- hau - 18th Aug 09
@Chris: I've heard something similar. The callose forms a wall that will block most structures attempting to pass through. This way they can block some pathogens. As far as I know, some microorganisms have the ability to break down the Callose wall, sadly. @hau: According to this fact sheet http://npic.orst.edu/factsheets/Capgen.pdf. It is mentioned that capsaicin is believed to protect the seeds against particular pathogens. I think plants have an immune system we have a hard time to imagine . The responses available against a pathogen attack depends on the plant and the compounds it hold. Not long ago I read in a Science Magazine that the plants enzymes and proteins that can disintegrade the cell wall of the attacking microorganism. Hopefully someone can confirm this . - DrChemistry - 18th Aug 09
Forgive me I had to: Plants have immunity only when the DA accepts their plea bargain. ( runs and hides) - Edster - 19th Aug 09
You should read this recent article in Science Magazine's Origins blog: http://blogs.sciencemag.org/origins/2009/07/on-the-origins-of-plant-immuni.html It explains at the beginning that plants don't have an adaptive immune system (mainly because of the lack of a circulatory system) but they do have an innate one. The article then carries on to present the state of the art on why the innate immune system of plants and animals is so similar.
- mudd1 - 24th Aug 09
Salicylic acid (aspirin) is used as a signaling molecule in plants that leads to a immune-like response. One of the resulting responses is cell death, as mentioned previously. "Systemic Aquired Resistance" is the term to look up to learn more. It is not specific to a particular pathogen, however, so it is more like our non-specific immune responses, not like the B-cell mediated immunity.
See the whole discussion | Make a commentThere was some research a while back that also plants can signal each other through a hormone, jasmonate, to warn of a pathogen! - Jessica H - 7th Sep 09
| |
Weighing Buoyancy
Does a glass get heavier if you put your finger in the water? Find out in this experiment.
What you need
| 2 plastic glasses |
| A stick |
| String |
What to Do
The idea is to build some scales, with a glass of water on each side. So first you want a way of attaching the cups to some string.
One way of doing this is by cutting two holes in each cup, slightly below the rim.
Then tie the cups to the stick, and attach a piece of string to the centre of the stick.
Now fill the two glasses almost full.
Add water so that the stick balances when hung from the centre piece of string.
Put your finger in one cup, without touching the sides. What happens?
What may Happen
You should find that the cup you put your finger into, moves downwards.
What is going on?
One way of thinking about this, is that if you put anything in water - a boat, a rubber duck or just your finger, it will feel an upthrust force pushing up on it. This is the force which makes boats float, and is equal to the weight of water that is displaced by the object.
Issac Newton worked out that if you apply a force to something, you will feel an equal and opposite force (every action has an equal and opposite reaction). So if the water is applying an upwards, upthrust force to your finger, your finger must be applying a downward force to the water.
|
|
|---|---|
Another way of thinking of it is that when you put your finger in the water, it will increase the level of water in the cup. This means that there is more water pressure at the bottom of the cup, acting on the same area, so there is a greater force.
Written by Dave Ansell
Information presented on this website is the opinion of the individual contributors and does not reflect the general views of the administrators, editors, moderators, sponsors, Cambridge University or the public at large.
The contents of this site are © The Naked Scientists® 2000-2012. The Naked Scientists® and Naked Science® are registered trademarks.