 |
Podcast TranscriptThe Naked Scientists: Science Radio & Science Podcasts |
Superhero 3D X-ray vision
|
Splattered windscreen bugs unveil a biodiversity treasure-trove
How many living species are there in the world?
It’s a huge question that no-doubt comes with a really huge answer. But finding that answer is no mean feat. Sending scientists out into the world to find, describe and name all the living things there are is a massive task.
Now scientists from America have come up with a possible new way of making the process a lot quicker and easier, and it involves scraping the splatter of dead bugs off a car windscreen.
In a paper in the journal Genome Research – freely available online - a research team led by Anton Nekrutenko of Penn State University have developed a piece of free online software called Galaxy to help make it easier to estimate biodiversity based on DNA sequences extracted from the environment – a process known as metagenomics.
Until now, metagenomics has been used to assess the diversity of microscopic creatures, including bacteria living in deep sea sediments or on the surface of human skin. Essentially it involves taking samples from the environment, reading sequences of DNA from those samples and using that to estimate the number of different species present in that environment.
If enough of the organisms present in your sample have already had their entire genomes sequenced, then it is possible to know what particular species live there.
The big problem with doing this is sifting through the vast amount of information that metagenomics generates. How do you go from having a bunch of DNA sequences to gaining a meaningful idea of the diversity of species in your samples?
That’s where Nekrutenko and colleagues come in. They’ve created a metagenomic pipeline – information in one end, results out of the other – for other researchers to use and develop to make this whole process simpler and quicker.
They tested it out by driving two cars, one from Pennsylvania to Connecticut, and another from Maine to New Brunswick in Canada. They then collected the squashed insects that landed on the windscreens of the two cars and sequenced the DNA in each sample.
The team identified a number of insect and bacteria groups in their samples, and interestingly discovered a difference in the diversity of the two samples.
Clearly, the number of species that can be identified is limited by the number that have had their genomes fully sequenced. But the hope is that as sequencing techniques become easier and cheaper, the catalogue of available species will expand rapidly in the future.
As techniques like this develop they could provide a useful tool in rapidly assessing biodiversity in the world around us, for example to study the impacts of all sorts of human activities on wildlife.
References | |||||
| - Kosakovksy Pond et al (2009). Windshield splatter analysis with the Galaxy metagenomic pipeline. Genome Research. | |||||
11th Oct 2009
Memory Chip Camera
Digital cameras have got immensely better and far cheaper over the last 20 years but they are still not perfect . They are still expensive and complicated partly because they are analog devices, each pixel converts light into a variable amount of charge, and then circuitry has to digitise this voltage converting it to a number normally from 0 to 256. This also means that they don't have a large dynamic range - they are bad at taking photos of bright and dark things at the same time, as you run out of numbers.
Edoardo Charbon from the Technical University of Delft, in the Netherlands may have a solution: Get rid of the analog part entirely and make each pixel only return a 1 or 0. 
This might sound like a stupid way of getting a good image, but because this means that each sensor is so much more simple you can get at least 100 times more sensors onto your chip if not more. And because sensors of this size tend to be quite noisy - they will sometimes read a 1 when they should be reading a zero. You can group hundreds of them together and the total number of 1's will change smoothly with the light level.
The really useful bit is that because of the statistics, the value you read out will change very rapidly with light level when it is dark, but slowly when it is light - in the same way as your eyes, allowing you to take photos of bright and dark objects at the same time.
All the sensors you are using to collect light for one pixel don't have to be in the same place, so you could build a camera with hundreds of small lenses on an image sensor which software then overlays to produce a good image. Allowing you to make the camera extremely thin.
This would all be very interesting if it was expensive to make these new chips, but it turns out that conventional memory chips are light sensitive if you strip off their black plastic. and they have billions of sensors so are ideal for this type of operation, although they may not be optimised for collecting light, so might not catch so much light.
References | |||||
| - The Gigavision Camera | |||||
10th Oct 2009
Fisheries mixed up by climate change
More predictions have emerged of how climate change is likely to affect the planet. This time, scientists from the Sea Around Us project based at the University of British Colombia in Canada, have turned their attention to how the shifting climate could impact the world’s fisheries. And as you might imagine, it is not good news.
Within the next 50 years, catches of fish in the tropics could drop by 40% because of the changing climate. However, in areas further north and south, fisheries could in fact expand by as much as 30 or even 70%.
William Cheung, Daniel Pauly and colleagues have run computer models of over a thousand marine species encompassing around 70% of the world’s fisheries, ranging from krill to sharks, plugging in environmental and biological factors that affect their distribution.
The team then ran a simulation of how those factors are likely to change and hence how fish populations will respond under two different climate change scenarios – although not including the worst case scenario that the International Panel of Climate Change (IPCC) have put forward.
Under these models, certain countries will see fish disappearing from their nets, including Chile, China, the US and Indonesia. And that is simply because fish will not tolerate in higher temperatures.
Fish that can swim far enough, could potentially move to cooler waters in the north and south. This is why the models predict increased fish catches in some countries notably Russia, Norway, Greenland and Alaska.
Fish that aren’t able to swim far enough could go locally extinct as the climate changes.
For people living in poorer parts of the world who rely heavily on the sea for a source of food and income, this could spell disaster, especially given that other studies predict that climate change will lead to on-land food shortages in similar regions.
Published in the journal Global Change Biology, the results of this study are likely to be a conservative view of the changes that are due to come. The researchers did not, for example, consider how the increasing acidification of the oceans will affect fish distributions.
And of course, with predictions of the increasing collapse of fisheries due to overexploitation, the overall prognosis for the oceans is not a good one.
11th Oct 2009
Tiny nuclear battery
Modern electronics is getting smaller and more capable all the time, and all sorts of sensors and communication systems are being developed to sense chemicals, forces, etc and communicate them back to a base station. But you still have to power the systems, and chemical batteries have a limited life, and get less efficient in space as they get smaller.
One obvious incredibly high density form of energy is from radioactive decay. Thi s stores at least 100 times as much energy as the same amount of chemicals. The problem is getting the energy out. Various spacecraft generate energy from the heat produced by the decay but this is inefficient, particularly in high temperatures, and doesn't scale down well.
Another approach is to use the radiation to directly stimulate a structure like a solar cell, which will produce electricity in the same way as it would with light, this can be scaled down to be very small. The problem is that the radiation damages the crystal structure of the semiconductors in the cell and makes them less and less efficient.
Researchers at the university of Missouri may have come up with around this problem - use a semiconductor which is not crystaline and is in fact a liquid. they have used Selinium and radioactive Sulphur 35 as the radioactive source to produce a battery smaller than a 2p coin. It is at present not very powerful about 16nW with an effciency of about 1.2% which doesn't degrade over time.
This is not very much power but enough for some applications and of course this is very early days so it should get a lot better with new developments.
References | |||||
| - The nuclear battery | |||||
| - Preparing the radioactive source | |||||
11th Oct 2009
The 2009 Nobel Science Prizes
Richard Van Noorden, NatureChris - Well also this week, we’ve of course have the Nobel Prizes being awarded and before that, the IgNobel’s - but that’s a different story. And we’re joined now by Richard Van Noorden who is an Assistant News Editor with Nature and he’s going to tell us a bit more about them. Hello, Richard.
Richard - Hi, Chris.
Chris - Welcome back to the Naked Scientists. So tell us a bit about the Nobels this week. Who got what?
Richard - Well interesting that you should be talking about cameras and CCDs and how to turn lights into electronics because the Physics Prize this week went to Willard Boyle and George Smith for their work on inventing the CCD, the thing in your digital camera that turns optical light into a digital picture. And also, to Charles Kao and he worked on fibre optic cables, those billions of kilometres of fibre optic cables spanning the globe and the light bounces along inside them by total internal reflection. And it’s a very efficient way of carrying the signal.
Chris - Indeed, we couldn’t basically have the internet without fibre optics, could we?
Richard - Exactly, so. Now the other prizes in Physiology or Medicine went to Elizabeth Blackburn, Carol Greider and Jack Szostak for the their work on telomeres. These are essentially the caps at the end of your chromosomes, the things your DNA is wrapped up in and they’re sort of protective caps. What Blackburn and Greider and Szostak found was exactly how these telomeres work and what they do. What happens is, whenever your cells divide you need to make new cells, and you need to copy your DNA. The DNA polymerase, the enzyme that reads your DNA can’t quite read to the end of the chromosome and it would get frayed like a piece of frayed string. And you can imagine your cells would keep dividing and your chromosomes would keep fraying and in the end, your DNA would actually degrade. And what these telomere caps do is they add on to the end of the chromosome, they’re repetitive DNA structures, they keep getting built in there every time. And so, they prevent the cells that carry them from degrading, but you also need an enzyme to build them up called telomerase, that builds up the telomeres. This is for example, is what you have in cells that are immortal. Cells that never ever stop dividing.
Chris - Cancerous cells?
Richard - Yes, cancerous cells. So many, many cells that turn cancerous also have this enzyme telomerase. But not just cancerous cells. Also stem cells, those cells that can turn to into many other different types of cells. So, what they did, what Blackburn and Greider and Szostak did, is work out how these process is working and what the structures are. And nowadays, the hope is that we could perhaps use this to understand stem cells better possibly to attack tumour cells, cancerous cells, and really, the possibilities are endless here.
Chris - What about Chemistry, another subject dear to my heart?
Richard - Yeah, Chemistry Prize. Another biological prize interestingly enough. It went to Ada Yonath, Venkatraman Ramakrishnan who works in Cambridge just a few miles away from where you are and Thomsa Steitz in the US. And their prize was for working out the structure of the ribosome, the protein-making factory in all of our cells. What the ribosome does is it takes DNA which is, as it were, the blueprint and then it has to translate that into the proteins, the things that actually do the work in your cells that buzz around, and do all the reactions. And Yonath back in the 1980s decided that this enormous ribosome structure contains over a million atoms, she decided that she’d try to crystallize it so you could bounce x-rays through it and from the way they were scattered, work out where the atoms were. Everybody else thought this was a ridiculous idea, but she did manage to crystallize some ribosomes by taking some ribosomes from organisms that lived in the dead sea, at very high temperatures. Their ribosomes are very stable and easier to crystallize. And then Ramakrishnan and Steitz came along and they worked out the exact structure of the ribosome. They actually completed this task in 2000. Now, what’s interesting about this is we’re now just working on antibiotics that can attack the ribosomes of bacteria. Remember, you need your ribosomes to make proteins. So, what we’re trying to work on, in fact, Steitz’s group have a company that are doing this, is to get antibiotics that by attacking ribosomes, prevent bacteria from making proteins. And therefore, stop the bacteria dividing. This could be a way to basically attack bacteria that have become resistant to the antibiotics we have at the moment.
Chris - Fantastic. Well, Richard thank you for joining us to tell us all about that and we’re going to ask you to comment on the Peace Prize, somewhat controversial of course. Thank you very much. That’s Richard Van Noorden who is from the journal, Nature bringing us up to speed on this week’s Nobel Prize winners.
October 2009
Technology in India
Chris Vallance & Jamilla Knowles, BBC CorrespondentsHelen - Now it’s been a while since we’ve had an update on the world of technology. So it’s time to join our resident expert Chris Vallance for a summary of what’s been going on over the summer as well as insight into the social effects of the technology boom in India.
Chris V - Well it has been a while since we spoke and in the intervening months I think there were two events which for me highlighted the way that technology is changing and I think we should talk about. You’d have to have been hiding under a rock to miss the first one, that’s the 40th anniversary of the Apollo Moon landing. Obviously the Apollo Moon landing is important for technology as it’s the early uses of things like integrated circuits, fuel cells. Obviously people debated and discussed the contribution to technology that those landings made. But certainly events that are very important for people with an interest in space and the technologies surrounding it. And we
fast-forward to September and we have the announcement that one of the new countries to enter into space exploration; India, the Indian Chandrayaan probe had discovered evidence of water on the moon. Now it’s interesting for us to talk about India at the moment because obviously everybody hears about the Indian tech boom and what that means for the country. A lot of it focused around the city of Bangalore. One of my colleagues has just been there: Jamilla Knowles, who’s been looking at what this most tech-enabled of Indian cities can say about how technology is changing, the social relations in India between the haves and the have-nots. Obviously a country where there is still a great gulf between those two groups. What did you find?
Jamilla - I found things that you would probably expect if you start reading about Bangalore the area of poverty, the population is as huge in comparison with those who are employed, say. And also that there are huge areas throughout the city of migrant workers living in slums, basically building glass shiny edifices to technology that we use. So it’s quite stark but it’s something that has been happening for the last decade or so. So it’s looking more at the kind of politics and the consciousness of people who are in Bangalore as a city. I went across to the Centre for Internet and Society inspecting Nishant Shah there, who’s the director of research. And he was talking about a sort of a feeling and a consciousness generally of people having a relationship with the internet and that would be even people who have never even used a computer.
Nishant - So the case study in Ahmdebad, which is where the people who were living in slums on the river front, on the Sabarmati river front, are now demolishing their own houses and are being employed by the state to do that in order to build an IT skyline for the city. There is no resentment among the people, there seems to be no protest initiated by civil society organizations. And when you kind of talk to the people they keep on telling you it’s because of that internet. And they’ve never seen a computer and they’ve never been online and they don’t know what the internet is about. But they imagine themselves as having access to the internet by building this particular kind of infrastructure. These are the invisible people of the IT story. These are people we no longer talk about. We always talk about either people in call centres or in back processing offices or offshore development centres or you know start ups who are working on technology. People who are visible and who have a voice and who are so quintessentially a part of technology that we forget that there is an entire support system which is also defined by internet technologies in India. And then we start talking about IT cities and IT parks and so on but are these people who aspirationally or experientially a part of the internet paradigm but not the technology. 
Chris V - So that’s fascinating. So people who are the very poorest people in Bangalore, completely separate from the tech boom have this idea of the internet but they’ve never actually used it.
Jamilla - It’s almost as though it’s in the air, it’s everyone from auto rickshaw drivers from children in schools that are really in need. These are kids who live with their parents who move around the city looking for work as labourers and often suffering from skin conditions from malnutrition. But they understand, they know why their city is changing.
Chris V - Is the internet benefiting these people in any way apart from the economic benefits?
Jamilla - What are they getting direct benefits from the internet is difficult to say. Some of the online companies will say yes because they will go to rural areas and show local people or farmers, “Here’s the internet it’s great,” but essentially they’ll put it on a bus which will then drive away again so it’s quite difficult to see that. Going back to things like education which seems to be underpinning their hopes for improvement. They are doing things like sourcing information online in educational centres then burning CDs which become educational supplements for teachers in rural areas. Because they may not have the skills in say the sciences or mathematics that maybe teachers who are in urban areas do, so they can actually record a lesson and send it out and supplement that with information that they found online.
Chris V - Did you get a sense that there are almost two cities, the bright shining new city and there was the older city of people who didn’t have access to the technology?
Jamilla - Definitely and it’s quite often the migrant workers from other states who don’t have the access. Local people in Bangalore have a slightly different argument with the fact that basically they’ve been overrun with people from all over the world and all over the country thinking of Bangalore as one of the places that might be paved with gold when it comes to employment. And instead there’s a great deal of unemployment and it’s happening to them as well because the population has just exploded and they're not necessarily trained up to go and work in IT support, to go and work in a call centre, to go and work as a developer or coder. I mean, that’s far beyond the ken of many of the people who live there.
October 2009
|
Can Plants get Cancer? |
|
Chris - Cancer in the context of a human has got a specialist disorder. What we mean by cancer, our cells that have lost the ability to obey the normal signals that control and dictate how things grow and move and obey signals that tell them not to go to other places in the body and not to grow through boundaries of tissues and not to disobey ‘kill yourself’ signals. Because every cell in the body is programmed to die unless it’s told otherwise. Cancer cells ignore that signal and so, they are immortal as Richard Van Noorden was saying, and they also disobey all those normal regulatory signals that can spread to other bits of the body and cause secondary tumours. And it’s usually those secondary tumours that cause problems. Now, plants don’t have a disease like that. They don’t get secondary spread through their system of disease which starts in one part of the plant and goes elsewhere, at least in the form of the cells from the plant itself. But they can get localized growths, a cancer-like phenomenon and just like some human cancers which can be triggered by microorganisms, cervical cancer for example is caused by infection with a virus, human papilloma virus. Also, gastric cancer in the stomach is caused by bacterial infection, Helicobacter pylori, is strongly associated with gastric cancers. In plants, there is an environmental organism, it’s called Agrobacterium tumefaciens, this is a soil dwelling bacterium and it has something called a transposon. This is a piece of genetic material which the bacterium injects into the plant’s own genetic material and that transposon carries genes which code for growth factors. And it causes the plant cells to begin to grow out of control. And the idea is to produce a big growth locally on the plant that then gives a home and provides protection to bacteria and that’s a Gall. And it’s very, very common, it’s called Crown Gall disease when the plants actually have it, but it doesn’t spread predictly to other bits of the plant. So there are some similarities between human cancers and animal cancers and plant tumours like Crown Gall disease, but it’s not the same disease. There’s nothing systemic as far as I know that does the same thing but it’s a very good question. |
|
October 2009 |
|
|
Why is glass transparent?Why is glass transparent? I’ve heard that glass can be made from sand. How is this given that sand is not transparent, you can’t see through it, but you can see through glass? Neil Denom |
|
Well if you look very, very carefully at a single grain of sand, especially if you’ve polished up the surfaces, it is actually transparent. I’ve looked through lumps of sand, quartz- white sand, through microscopes. As long as it’s polished, you can see through it. Sand is intrinsically transparent. The reason why you can’t see through it on a beach is because it is in lots of lumps. If you ever looked at the world through a glass or a piece of glass, especially if it’s curved, everything looks distorted behind it because when light hits it, it slows down, it bends, it goes around a corner it gets refracted, and the light kind of gets bounced off. Now, if you're looking at something large, you can still make up a picture behind that. But if you’ve got thousands and thousands of very small glasses, the light would all get refracted off one. It would get refracted offsome others, and all the pictures will get mixed up and mixed up and mixed up, until eventually they get overlaid over one another and it looks white. Chris - So it must be the same phenomenon as snow looking white, but the water it’s made from – if you see it in fish tank, is transparent. Dave - Yeah and even in ice it’s also transparent. Helen - And then you’ve got sort of yellow sands, black sands, and the other impurities that are giving it that kind of tinge of a different colour path. Dave - Yeah, you get different rocks in it. Black sands are normally from basalts which is intrinsically black and those just aren’t transparent and yeah, a bit of patchy clays and all sorts of things in there. |
|
October 2009 |
|
|
How do cold-blooded species cope in cold water?How do cold-blooded species cope in cold water? We all know that reptiles have to sun themselves to build up the energy or ability to sustain their activity and to get to the right temperature. And this is attributed to the fact that they’re cold-blooded. How is it then possible for other cold-blooded species like fish and invertebrates like octopus, squid and so on to sustain the high levels of activity that they do, that they can live in near freezing or actually freezing water? John Harrison |
|
The answer is to do with their metabolic rates and the fact that they can operate at those low temperatures. I actually want to go into detail a little bit on what you call at the end, the freezing species. This is the most interesting thing that was discovered back in the 1960s which is that there are fish in the Antarctic that create antifreeze and that’s how they live in very cold temperatures. Because the crazy thing about the sea is that it doesn’t actually freeze until -1.9 degrees centigrade where as normally water freezes at zero, we know that. But it’s because of those salts and the various impurities in seawater that means that ocean temperatures can get extremely low indeed especially down there in the southern ocean. And so these Antarctic cod it was discovered that they have glycoproteins in their blood. That means that their tissues their fluids inside them don’t freeze until -2 degrees centigrade, so they are safe in the sea. The glycoproteins work in a very clever way by actually attaching to the surface of small ice crystals by plugging gaps if you like between them. And that stops them from getting any bigger so the fish themselves don’t actually freeze despite the fact that they are sub zero in temperaturesand that’s really rather cool. But then there are other reasons why they don’t actually manage to swim around all the time and they are affected to some extent by what temperature there is and what’s going on in the environment. Because it was discovered last year that some fish in the Antarctic hibernate. The first fish that were shown to actually slow down, slow their heart rate, slow their movements when it’s very cold and dark. And that could actually be because it’s dark and they need to be able to see to be able to catch their food. So in fact what they do is say, “Okay fine we’ll have a bit of rest while we can’t find our food and wake up when it gets warmer and lighter.” |
|
October 2009 |
|
John Harrison asked the Naked Scientists:
Cold Bloodedness: We all know that reptiles must sun themselves in order to build the energy / ability to sustain activity. This attribute is generally attributed to the fact that they are cold blooded.
How then is it possible for other cold-blooded species (fish, invertebrates such as octopus, squid, etc.) to sustain high levels of activity in near freezing water?
What do you think?
- John Harrison - 26th Jun 09
For an important chemical reaction, poikilotherms may have four to ten enzyme systems that operate at different temperatures. As a result, poikilotherms often have larger, more complex genomes than homeotherms in the same ecological niche. Frogs are a notable example of this effect.
See the whole discussion | Make a commentBecause their metabolism is so variable, poikilothermic animals do not easily support complex, high-energy organ systems such as brains or wings. Poikilothermic animals do not use their metabolisms to heat or cool themselves. For the same body weight, poikilotherms need half to 1/10 of the energy of homeotherms, and thus eat half to 1/10 of the biomass. source: http://en.wikipedia.org/wiki/Poikilotherm So to answer your question: They have specialized enzymatic systems. - Nizzle - 18th Aug 09
| |
|
Why does water expand when it freezes? |
|
Basically, the default thing for things to do is to shrink when they freeze because normally, if you make something hotter, it’s vibrating more. When it vibrates it tends to take up more space, so it tends to expand. Ice is very unusual that as it gets colder, although it’s essentially vibrating less, it does expand. And the reason for that is due to the strange shape of water. If you’ve ever seen the picture of a water molecule, it looks like a Mickey Mouse head with an oxygen molecule where Mickey Mouse’s face is and then two hydrogen atoms where his ears are, it’s bent basically. The oxygen atom is slightly negative and the hydrogens are slightly positively charged, so water molecules tend to stick together forming what are called hydrogen bonds. And because of that bend, the way they tend to link together is actually a very open structure with big holes in it and that means, there’s quite a lot of extra empty space in that structure. So when water freezes it, it releases a load of energy because lots of extra strong bonds can be made. But it does take up more space. And so, ice expands when it freezes. |
|
October 2009 |
|
I can't answer all your questions, but i can answer some. Why does water expand when it's freezing: because it's maximum density is at 4°Celcius. This is also the reason why water is fluid under great pressure. You won't find any frozen water pockets on the bottom of the ocean neither, because the pressure will make the water be at it's maximum density. Maybe someone else can explain why the density of Ice is lower than 4°C water... - Nizzle - 17th Aug 09
I'll give it a shot, see if I'm correct As you know, water is a really characteristic compound in comparison to other compounds. Many compounds contract when they are frozen, just like your thermometer drops when it gets colder. Water differs because, as Nizzle correctly stated, it's maximum density occurs at 4 degrees celcius. This means that below 4 degrees celcius it can do nothing but decrease its density and expand, as it could not have a greater density (The exact reason why ice floats). Another thing which plays a role is its polar nature. What basically goes on here is related to its structure and polarity. Water has an sp3 hybredization, but due to what we call "Valance Shell Electron Pair Repulsion" (or short VSPER Theory), the angle between the centered Oxygen atom and two hydrogen atoms is about 105 degrees. I will return to the structure in a moment. Water is also polar. Oxygen is more electronegative than Hydrogen and greedily pulls Hydrogen electron towards itself. This makes Oxygen slightly negative, and hydrogen slightly positive. This enables water to form what we call 'Hydrogen Bonds' (Process: Hydrogen Bonding). In water these bonds will form, break and form again on a new. Freezing causes less molecular activity because it means it's a drop in energy. Hydrogen bonds become more stable, and order themselves as a quite spacy hexagonal structure, due to its structure (It expands, taking up more space). I am not sure what force it exerts when expanding though P.s. I should add that this is for 1 atm (Atmospheric Pressure), which is the equivalent of 101325 Pa. Also as Nizzle stated, greater pressure ensures water as liquid. - DrChemistry - 17th Aug 09
The answer was helpful, though I have a follow up question. If the water is in a confined space, say a bottle, before freezing, then once all the water has frozen the air pressure inside the bottle rises. This must meen that the air inside the bottle is not filling in that 'space' inside the ice crystals. Does this meen that inside these cystals is a vacuum or is it just that air is inside these crystals but at a lower pressure to the surrounding atmosphere? If not, what exactly fills these crystals?
See the whole discussion | Make a comment- Richard - 10th Feb 10
| |
|
Why can't the human body multi-task?Why can't the human body multi-task? If you turn your right foot and move it slowly in a clockwise circle. So you're going round in a circle with your foot. Then writing a number 6 with the same hand that you're moving your foot on a piece of paper. But the better way to show this actually is to take your hand on the same side of your body as you're moving your foot. Now, try and make that move in a circle in the opposite direction to your foot.The foot follows the hand. Why does that happen? Steve |
|
It’s very, very difficult. You can do it with practice, but it is incredibly hard to do. If you try and do that number 6, you’ll find that number 6 flips around, and you start drawing it backwards. And the reason for this is to do with the way your brain codes for movement. Because you can easily do that if you use the opposite sides of the body. If you’ve got a hand which you do a clockwise circle with and your right hand and then you use your left leg, you’ll easily do a circle in the anticlockwise direction because you're using two different sides of your brain. If you're trying to use the same side of your body, the motor cortex which is the bit of the brain which codes for movements, the way this is working is that it doesn’t actually code for a brain cell, telling a muscle what to do. The brain actually codes for movements by what’s called a tuning curve. So you have a cluster of nerve cells which fire off when you want to make a movement with a part of the body into a certain direction in space. And those nerve cells don’t just switch on muscles that move say, just the arm. They switch on muscles which would move your leg in the same direction too, but they turn them on a bit less than the motor neurons that control the arm. So basically, you're facilitating or making it easier for your leg to move in the same direction as your arm. But it takes a little bit more switch on to make the leg move as well. Therefore, if you try then to make a movement in the opposite direction with the leg, you're basically facilitating another group of nerve cells to move in the opposite direction. So the two things are trying to fight it out and it’s, whichever one wins, actually ends up going in that direction, and the arm is such a dominant force that’s somewhat brain devoted to it, that I think it probably overwhelms the signal for the leg which is why the leg finds it hard to be dominant in that way. But it’s an amazing demonstration, isn’t it? It’s great fun. You can have a lot of fun with that at parties. |
|
October 2009 |
|
|
Are 'light' cigarettes better?Is there any actual benefit from smoking a light cigarette as opposed to like a full strength one? Andrew |
|
Chris - James Bond said that giving up smoking is actually really easy. He’d done it hundreds of times. The thing with smoking is of course, everyone takes these or uses these ‘light’ or kind of ‘smooth’ cigarette brands. They first surfaced in the ‘50s and ‘60s. I was doing a bit of research of this because I thought they were more recent than this. But they first surfaced in the ‘50s and ‘60s actually, coinciding with when Richard Doll first published studies, showing that smoking is bad for you. So, it was a sort of response in the part of cigarette manufacturers to try to market a product that gave the impression that it was in fact much healthier. And in fact, 80% of the cigarettes that gets smoked worldwide are now of the ‘light’ variety. And the way they make them ‘light’ is that they put little holes in the filter. And so, as the person takes a drag on the cigarette, it draws in some air with the smoke. But what that means is, this can actually lead to a change in behaviour on the part of the person. And in fact, the statistics show that in fact, smoking ‘light’ cigarettes is no better for you than smoking full strength cigarettes. And the reason is, people change their smoking behaviour to accommodate the fact that they're getting a lower nicotine dose. There was a study which got published in the journal, Neuropsychopharmacology was a guy in UCLA in America, Arthur Brody did this last year. They got people who smoked into the laboratory and they did a thing called a PET scan. This is a way of imaging the brain and they got them to smoke cigarettes and they compared people smoking cigarettes that had nicotine in them with cigarettes that have very little nicotine in them or much lower doses, to see how many of the receptors for nicotine in the brain got filled by these different varieties of cigarettes. And they found almost the same amount of occupancy. The receptors are getting stimulated, just as much. Probably because the people were smoking the ‘light’ cigarettes harder to get the dose up. Because at the end of the day, the cigarette has got nicotine in it and that’s the thing you want. So, people will just titrate up or increase their dose of cigarettes, in order to get their nicotine levels to what they want it to be, to satisfy their craving. I went looking for any actual evidence that light cigarettes are better on the internet and I found this site, the US National Cancer Institute. This is a government organization. They've got a very interesting analysis on this on their website and I’ll just read it to you because I couldn’t add anything to this. I couldn’t put it better myself, but this is really quite staggering. Listen to this: “Tobacco companies designed light cigarettes with tiny pinholes on their filters. These “filter vents” dilute cigarette smoke with air so that when lit cigarettes are “puffed” by smoking machines, and that’s how they get their tar numbers in the nicotine values which they then report in the packet, these causes the machine to measure an artificially low tar and nicotine level. But many smokers do not know that their cigarettes have these vent holes and the filter vents are uncovered when the cigarettes are smoked on the smoking machines, but the filter vents are placed just millimetres from where a smoker puts their lips or fingers when they're smoking. And as a result, many smokers block the vents when they smoke and this actually turns the light cigarette into a regular cigarette. Some cigarette makers also increased the length of the paper wrapped around the outside of the cigarette filter and this decreases the number of puffs that occur during a machine test. Although the tobacco under the filter is still available to the smoker and this tobacco is not burned during the machine test. As a result, the machine measures less tar and nicotine than is actually available when the person smokes.” And here’s the real clincher. Because smokers, unlike machines, crave nicotine, they will inhale more deeply, take larger, more rapid, or more frequent puffs or smoke a few extra cigarettes each day to get enough nicotine to satisfy their craving, and this is called “compensating,” and it means that smokers end up inhaling more tar, nicotine, and other harmful chemicals than the machines would actually have you believe. So that’s actually on the U.S. National Cancer Institute’s cancer.gov website. So, I think the answer to your question is, ‘light’ cigarettes are basically a way of making you smoke and think you're doing yourself some good. There’s no evidence that actually help people improve their health or give up. |
|
October 2009 |
|
|
Why does it get dark at night?Late last night when I was looking at the stars I was struck by a thought which I would like/expect to see/be proven wrong.. Since the consensus is that the universe is infinite, there should be a (close to) infinite number of stars, and quite a bit of these emit light. (Since quite a bit of infinite is .. ah well.. infinite, an infinite number of stars are throwing their light at us, 24/7 so to speak. Now is my question, why does it get dark at night? Gerjon de Vries |
|
Dave - It’s actually a really quite a deep question. If the universe is infinite, then any direction you look in, you ought to end up hitting a star. And therefore surely, the whole sky ought to be bright white. The simple answer is, because the universe is expanding, the universe is expanding really quite fast. So, the further away you go, it’s expanding as if you're blowing up a balloon. So the further away you go, the faster things are moving away from us. If you go a really long way, tens of billions of light years away, they’re moving away so fast that all light coming from it has been really, really red-shifted. So, it’s been so red shifted,that we can’t see it. In fact, it has been so red shifted that it’s in the microwave region in the spectrum. So you can see light in every direction, but it’s been so red shifted that our eyes can’t see it. So the sky looks dark. |
|
October 2009 |
|
|
How many LCROSS NASA missions would it take to change the orbit of the moon by 1%? |
|
Dave - Interesting question. What they were doing was firing the top stage of a centaur rocket and crashing it into the moon. They’ve been trying to watch the plume of stuff that comes up from that to see if there is water in that plume. Now the centaur rocket weights about 2.3 tons and it’s going at about 10,000 kilometres per hour, that’s 2,800 metres per second, which means it’s got 6.4 million (6.4 x 106) kilogram metres per second of momentum. That’s an awful lot of momentum. For anything on Earth, that’s a scary amount of momentum. However, the moon has got awful lot more momentum than that. It’s moving at a kilometre per second and it weighs 7.3 x1022 kilograms. That means the moon has got 7.3 x 1025 kilogram metres per second of momentum. So, how many LCROSS’s crashing into it would change it’s momentum by 1%? 7.3x1025 minus 6.4x106 is roughly 1x1019 So about 1019 collisions. So that’s 1 with 19 zeros after it (10,000,000,000,000,000,000!). And actually, an LCROSS’s momentum compared to the moon is about the same as 1 millilitre of water compared to all the water in all the earth’s oceans. |
|
October 2009 |
|
|
How do we know how much the moon weighs? |
|
Dave - We know quite accurately because we’ve sent things to orbit around the moon and the speed at which something orbits around an object is related to its mass and you can do it with a load of maths and workout exactly how much it weighs. |
|
October 2009 |
|
|
Do animals speak regional languages?Do animals speak regional languages? If I emigrated from South Africa to South America and I took my family dog with me, would his bark be understood by South American dogs? Jason Wrath |
|
Helen - Good question. Animals do indeed. Some of them do have regional accents, if you like, or dialects. And whether or not your dog would understand another dog might come down to breeds, rather than necessarily where it’s living in the world. But yes, animals do. We know that some birds have regional accents, some amphibians do, and if you jump into the oceans, there are creatures there that definitely have different languages and accents of their own. And that is the whales and dolphins, the cetaceans. And various studies have shown that if you listen to the sounds that some of these great whales are making, you can actually work out pretty well where it came from. Blue whales are one example and scientists have worked out that there are about nine regional populations of blue whales that seem to have their own distinct languages. And so, that might be something that has implications for things like conservation. Maybe we have to think about those nine populations as being slightly separate and different. Chris - Is that because the baby whales learn to speak by imitation from parents and that’s how this regionality arises? Helen - Probably. I mean, we know so little really about these amazing creatures, given the huge area of ocean that they live in, things like that. So these sorts of questions, we don’t yet know. For example, we also don’t know if they could understand each other between these regions. We don’t know that yet. Killer whales are another example of fantastic regional dialects. Along the eastern pacific coast of North America, there’s been a lot of study of killer whales living around Vancouver and Alaska. And these guys also have regional dialects. In fact, you can tell whether or not the individual killer whale belongs to a residential population, whether it’s a transient individual that’s coming through or whether it’s one from offshore because all these different killer whales basically speak with different accents, a little bit like different accents throughout the UK. We could tell where someone comes from, from the way they sound. I think this is fantastic. They've also shown that there's a genetic link which is fantastic which shows that there seems to be some way that killer whales can tell how related they are to each other. And therefore, try and avoid problem with things like inbreeding, just by the way that they're talking to each other. So I think that’s just really fantastic. |
|
October 2009 |
|
Jason Raath asked the Naked Scientists:
Hi Chris,
If I emigrated from South Africa to South America and took my family dog with me, would his bark be understood by the South American dogs?
Would animals on different continents speak different languages to each other? This would apply to cats, dogs, birds etc?
Thanks, love your show on Fridays on 702, and try never to miss it.
Cheers,
Jason Raath
What do you think?
- Jason Raath - 10th Sep 09
Whales have dialects.. I suspect that dolphins would as well.
- JnA - 13th Sep 09
One of the New Zealand Native birds, the Tui has regional dialects. That means that the Tui in Auckland can't understand the ones from Wellington and further south, and vice-versa. It's lucky that they aren't endangered or it would be a bit of an issue for breeding programs!
- Laura_Kelly - 13th Sep 09
"That means that the Tui in Auckland can't understand the ones from Wellington and further south" What do they know that's worth talking about? - Bored chemist - 13th Sep 09
Breeding for a start. And their songs are so beautiful and complex. If you want to have a listen, here is a link to an awesome recording of the Tui, http://www.radionz.co.nz/search?mode=results&queries_all_query=tui , then click on number 7.
- Laura_Kelly - 15th Sep 09
People are animals, so yes! :P
- Nizzle - 15th Sep 09
Well, we've seen evidence above that birds do show regional variation, but these are complex (and often, though not exclusively) learned behaviours. I would suspect that dogs & cats (and other animals with relatively simple vocalisations) would probably be able to understand each other. Not to mention the non-verbal communication, (scent, raised hackles, rolling over...) would probably also communicate across regional boundaries - it communicates well enough over species boundaries! - BRValsler - 15th Sep 09
Sheep in Northeastern Spain speak Baaaaasque.
- Geezer - 15th Sep 09
I think you mean Speech, not Language, as there's not real proof as of yet that animals use Syntactic (or even Semantic) Language skills (phonemes, morphemes, meaningful segments, etc).
Its an important distinction, since its one of the evolutionary qualities that appears to be uniquely human, and a likely indicator of Cognitive function.
- John G - 24th Jan 10
So you are all saying that all animals have language?...Or that their communication differs in dialect like a language would?
See the whole discussion | Make a comment- brea - 30th Jan 10
| |
|
Jelly fish swim in groups. How do they communicate to stay together?Jelly fish swim in groups. How do they communicate to stay together or do they communicate? Steve |
|
Helen - I don’t think they do actually. Jellyfish are in some ways extremely simple creatures. They don’t have a brain, so they don’t really have the ability to process inputs and sensory inputs like that. So, I think usually when you see large numbers of jellyfish together, it’s probably more likely to be, the fact that the currents and the ocean currents are actually moving them together and keeping them in similar places. Or also, they can respond to things like the availability of food in the water and chemicals and things like that. So possibly, they're all following food sources, and that’s why they're all ending up together. But I don’t think we yet have an idea that jellyfish can actually communicate to each other. Although some of them do have quite complex eyes, which is quite exciting and box jellyfish have eyes. They're actually quite... Chris - What do they do with them? Helen - That’s a very good question. They have eyes quite a lot like humans and in fact, some of the genes they have are very similar to human genes for creating parts of the eye, but we think that happens in parallel and wasn’t from a common ancestor, but we arrived at the same solution to having eyes and what do they see? We know they certainly respond to daylight, light and dark. They need to know basically, what time of day it is because they tend to come up the water column at nighttime when they're less easily seen by predators and when it’s light, they actually go further down the water column. So, they respond to light and dark. And even though they have quite complex eyes, it’s actually a very good eye at detecting things like diffuse light to figure out, is it light or dark? What time is it? Should I be up or down in the water column? |
|
October 2009 |
|
Steve asked the Naked Scientists:
Jellyfish swim in groups. How do they communicate to stay together?
What do you think?
- Steve - 6th Sep 09
Jellyfish can, but don't always swim in groups. Any degree of communication between jellyfish is likely to be by chemical means: the jellyfish will be producing and releasing various compounds into the water that can probably be sensed by other jellyfish, so it's probable that jellyfish have some idea of whether there are other jellyfish nearby, but I doubt that there's any meaningful communication between them. Neither do I think that they deliberately group together for mutual defense, as with flocking birds and schooling fish. With birds and fish it is the speed of the individuals that make the flocking/schooling tactic effective, by making it difficult for a predator to identify a single specific target. Jellyfish just aren't fast enough for this to work. I would guess that large groupings of jellyfish occur either because they've all detected the same concentration of food or because they all hatched in common region and, all reacting in the same way to the same common stimulus, haven't drifted apart yet. If all the jellyfish in a large concentration are similarly sized it suggests that they are all the same age and have grown up together. Conversely, if they are different sizes and species it would suggest that they have come from different places but have all detected the same source of food. - LeeE - 6th Sep 09
In addition to Lee's highly probable explanation, there is also the reproduction requirements. Jellyfish are both asexual and sexual reproducers. No mating takes place in sexual reproduction, the egg is fertilised by the sperm released into the sea. Proximity of the parents is therefore essential.
See the whole discussion | Make a comment- Don_1 - 7th Sep 09
| |
|
How far would electricity carry in the sea?How far would electricity carry in the sea? If a toaster, connected to the mains at 240 volts was accidentally dropped into the ocean, let’s say the North Atlantic, would the sea life be electrocuted? And if so, how far and how deep from the toaster would these electrical shockwaves travel? Marianne Dias |
|
Dave - Seawater conducts electricity reasonably well, but not very well. It’s about a 10 millionth as good as copper. So, you will get electricity flowing through it, but it will also depend on where the other cable is because electricity always moves from one place to another place. And if the other connection to the circuit is an awful long way away, then you get very, very small currents and it’s not going to do a lot of damage. If you’ve got two contacts a foot apart and a fish swims between them then it’s almost certainly going to get electrocuted. So, I think it depends an awful lot about how you set up this test. Helen - I just like to say, I don’t want anyone to go and try this for the sake of the fish and the sake of any divers that might be there. Just in case. Dave - And of course, with a toaster, if it’s got a proper three pronged plug, then you got an earth in there as well, so most of the currents can flow within the toaster from the live parts of the toaster to the earth. So, it’s probably not... Chris - It probably would just melt the cable, wouldn’t it? Dave - It’s probably going to draw a very large current and blow the fuse. Chris - I have heard of someone turning a lot of electricity into about a million gallons of very hot water in Australia when a flood happened in Adelaide at a Medical Research Institute and it flooded the basement and flooded the power board, and it didn’t trip out for some reason. It just passed a very large current through a large amount of water and made the largest Jacuzzi you've ever seen. So there we are. |
|
October 2009 |
|
|
Could I use a torch to push me in space?I’ve read that photons can push things and people have considered space ships propelled by large sheets or mirrors to catch sunlight. So, if I were in space and I had a flashlight powerful enough to push me, would it push me? ?And should I aim it towards myself or away from myself? Jesse, Ithaca |
|
Chris - Yeah and the answer is, it does work. In fact, there’s something called the YORP effect, Yarkovsky–O'Keefe–Radzievskii–Paddack effect in honour of the four scientists who described this first of all. If you look at asteroids and they are spinning in space and they're irregularly shaped, when they have one surface facing at the sun, which is a different size, say to the other face, then that face gets a disproportionately big push compared with when the object then turns on its side for example. And what this does is to create a push or a torque effect, which tends to steer the asteroid and change its path through space. And this is one effect which is thought to have unleashed this barrage of asteroids on earth that destroyed the dinosaurs 65 million years ago because out in vestiges of the early solar system near mars are whole remnants of bits of planet that failed to form. And there are these fairly big objects out there and they are subject to the YORP effect. So light can definitely push things along, and that could go for a person too. We know we can push spacecrafts via the same thing. This is the whole concept of solar sailing. You have a very big collector. And when photons are incident on it, then they can give it a bit of a nudge and we can work out how much of a nudge a photon, when it arrives, gives something. We know from the Planck constant, if you times that by the frequency of the light, you can work out how much energy is imparted by a photon, a particle of light hitting something, and I have to say very big thank you to Light Arrow on our forum who suggested a very neat solution to this problem. So basically, yes. Light can give things a push. If our astronaut who’s drifting around in space were armed with a laser beam and he were armed with a 3 kilowatt laser beam, then the energy, the nudge that he would get would be given by the equation F=w/c, where F is the force and it’s equal to W, the wattage of the beam divided by the speed of light. And if we put the numbers in, 3 kilowatts is 3 x103 that’s power of a laser. You divide that by the speed of light, 3 x 108. That would tell you that the force that the astronaut would feel through firing the laser would be about 10-5 newtons. On Earth, that would be the equivalent of holding up 1 milligram. In other words, about 1,000th of a gram. So, very small push but nonetheless, over enough time, given enough time, it would push the astronaut through space. You would have to point the laser in the direction opposite to which he wanted to travel. Dave - This is actually the ultimate rocket. You get the maximum push for every kilogram of stuff you throw out the back. So, if you want to travel a very, very long way, this is the way to do it. |
|
October 2009 |
|
Jesse asked the Naked Scientists:
Dear Naked Scientists,
I have a physics question. I've read that photons can push things, and people have considered spaceships propelled by large sheets or mirrors to catch sunlight.
So my question is, if I were in space and I had a flashlight (torch) powerful enough to push me, should I aim it toward myself or away from myself?
Thanks,
Jesse
Ithaca, NY, USA
What do you think?
- Jesse - 28th Sep 09
Most efficiently you would aim it away from yourself as though it were the output of a jet engine. Aiming it towards yourself would have a complex effect - if you were wearing a black, light absorbing suit, there would be no net force, but if you were wearing something that scattered the light, there would be some net force but a bit unpredictable. With all such propulsion systems creating rotation is a problem too. However, the force produced by a torch (even a very powerful torch) is extremely small and would not be a practical means of propulsion. - graham.d - 28th Sep 09
As graham.d wrote, it would be more efficient to aim the beam away from yourself. You can easily compute the push received back from the beam if you know the beam's power: F = W/c F = force; W = beam's power; c = light speed. Example: with a 3 kilowatt laser you receive a push of 3*103/3*108 = 10-5N ~ 1 milligram. Remember however that we don'y need to talk about photons in this case: light's push exist in the classical theory too = it's possible to prove from Maxwell's equations that electromagnetic radiation has momentum (and can have angular momentum too!) - lightarrow - 28th Sep 09
The momentum from light is what causes the push. The push however is miniscule compared to what was in example.
See the whole discussion | Make a comment- Mr. Scientist - 14th Oct 09
| |
|
Why should we sit far from the TV?When I was younger I was told not to sit too close to the TV. Is it an urban myth that it's dangerous to sit too close? Or does the TV emit radiation? Does this still apply to modern televisions? Claudia, Argentina |
|
We put this question to Andy Karam, adjunct professor at the Rochester Institute of Technology... Andy - Televisions really do give off radiation. But having said that, it’s only a little bit of radiation and it’s not that dangerous. What happens is that anything with a cathode ray tube, a tube where you shoot high-energy electrons at some sort of screen, when those electrons hit the screen, they give off very low energy x-ray radiation. This is the same way that x-rays are produced in regular x-ray tubes. So, if you're sitting close to a cathode ray tube, whether a computer monitor, a television screen, a radar set or anything else with that type of technology, you're going to be getting low doses of x-ray radiation.
LCD and plasma screens don't give off any radiation at all. They don't use high-energy electrons. It’s a different type of technology. I could not say that they're safer because I don't consider the radiation from cathode ray tubes to be a risk, but I can say that they give off less radiation. As far as sitting too close to the television goes, the further back you are, the lower the radiation dose will be. But having said that, I don't consider the radiation dose even at a distance of just one metre to be dangerous. |
|
October 2009 |
|
If you sit too close you block the grown-up's view. They can't sit so close because (generally) children have a better abillity to focus than adults. - Bored chemist - 6th Oct 09
TV sets presumably have to conform to industrial standards nowadays, that they emit minimal radiation. (Radiation is simply energy; it can be reflected, absorbed, or emitted.) Whether a TV set is bad for your eyes is a different matter. Your eye muscles are put under strain to focus images through the lens. If you are looking at something a short distance from you, they have to work harder. However, this doesn't cause long-term damage as such, as far a I know though (for most people.) - Shibs - 6th Oct 09
I was told the same thing also but that was in the 1960's. The early TV's had 405 lines and had a noticeable flicker to them. They also looked out of focus close up(from what I can remember). I don't think the public in those days knew much about TV radiation so I doubt that was why. IIRC The older CRT TV's emitted radiation but the forward radiation towards you is very low and not harmful. Most modern TV's now have LCD screens with higher resolutions, mainly flicker free and emit no radiation. Its amazing how quickly they've gone from being a heavy square box to a large wall-mounted set. - that mad man - 6th Oct 09
Urban Myth.. possibly stemming from a *little* truth. I agree with the mad man (never thought I'd be uttering those words again - sheesh!) it's less to prevent eyes damage and more eye strain. Before 1968 some sets emitted excessive X-rays... so I guess a blanket warning was given and it stuck.. like the perceived warnings of the microwave and eating lead... (wait that last one might be real) - JnA - 6th Oct 09
I always thought that CRTs emitted x-rays (albeit at low intensity) and this was the reason not to sit too close, so as to reduce the dose. But then again, unless they are coming off at very wide angles, the distance from the TV wouldn't make an enormous different to your dose would it, air not posing much of a barrier to an x-ray...
- chris - 7th Oct 09
It is not so much the angles at which these X-rays come off from a cathode ray tube that it is the issue. From the fount of all knowledge, apart from TNS CRTs can emit a small amount of X-ray radiation as a result of the electron beam's bombardment of the shadow mask/aperture grille and phosphors. The amount of radiation escaping the front of the monitor is widely considered unharmful. The Food and Drug Administration regulations in 21 C.F.R. 1020.10 are used to strictly limit, for instance, television receivers to 0.5 milliroentgens per hour (mR/h) (0.13 µC/(kg·h) or 36 pA/kg) at a distance of 5 cm from any external surface; since 2007, most CRTs have emissions that fall well below this limit Wikipedia. - Shibs - 8th Oct 09
"TV's now have LCD screens ... and emit no radiation. " Dark in here, isn't it. - Bored chemist - 8th Oct 09
I don't know about X-rays, but there is another good reason why you should not spend a long time staring at anything from a short distance, especially as a kid. This has something to do with the development of the eyeballs and short sightedness. A child's eyes are smaller than an adult's, therefore they have to grow as one reaches adulthood. During this growth period, it is important to keep an appropriate shape and size, so that the picture projected onto the retina by lens is sharp. The exact mechanism is still unclear, but it appears, that it has something to do with the relaxed state of the lens. When you look in the distance (infinity) your lens is relaxed. If you need to "focus" to look in the distance, it tells your body: "Your eyeballs are too small". So there is a growth response to distance the retina a bit farther away from the lens. This mechanism must have served really well in our evolutionary past, because humans looked in the distance quite often. But in the age of book printing, TV and the Internet it is not working that well at all. During growth we are staring at a monitor, and therefore our eyes are getting a lot of growth signals. So if you keep a distance from the TV it may help to prevent short sightedness. Or at least helps to have a less severe one. Here is some reference, I hope I didn't misunderstand it completely :) http://www.annals.edu.sg/pdf200401/V33N1p16.pdf - Kupac - 10th Oct 09
I don't agree. Every TV in my house is still CRT-based. There will be a long legacy of the old TV days before these old units are all replaced. Chris - chris - 10th Oct 09
I don't agree. Every TV in my house is still CRT-based. There will be a long legacy of the old TV days before these old units are all replaced. Chris Just exactly how much use is an TV screen if it doesn't emit light? Light is a form of radiation. - Bored chemist - 10th Oct 09
It may be quicker than you think if they are old units. The analogue TV signal will be switched off in July 2011 so unless they are all digital receivers or you have separate digital box receiver/adaptors they wont receive a signal. - that mad man - 10th Oct 09
Radiation intensity follows a 1/r2 law, so that if you double the distance to the TV, the radiation decreases fourfold. - jpetruccelli - 11th Oct 09
My father has a projector home theatre downstairs and apparently there's a rule of thumb that in a theatre viewing that the optimum distance is three times the height of the screen - meaning you have to be sitting 3x the heigh of the screen away for the optimum distance. This rule is used to determine where the seating and the speakers should go thereafer. I wonder if this rule would apply to the TV world? - RWeb - 13th Oct 09
it is true it aint to dangerous to sit near the television because i remember when my i was having an experiment with my guinea rat is eyes where still intact and the t.v was near it
- uzor - 15th Oct 09
Many people are led to believe that sitting close to a tv will damage your eyes in the long-term. I believe that was back in the day, where emissions were not properly regulated. Nowadays, tvs are optimized for human safety. As a general rule of thumb, people shouldn't sit close to the tv because it causes eye strain, just like sitting in front of a computer. Suggestions if you cannot see the picture, would be to get prescription glasses, or visit a Optometrist.
- Jonathan Madriaga - 10th Nov 09
my grandmother often said that.. we should listen more often elderly people
- Gall - 15th Feb 10
if you sit back then you can see the whole tv with out moving your eyes, and as BC said it blocks the tv for your parents, i try telling my daughter teat but does she listen when her favorite cartoon comes on
- geo driver - 16th Feb 10
why should we sit far from tv?
See the whole discussion | Make a commentbecause to avoid the ambiguity of our eyes...when we are too close it can damage our eyes...We should beware because we are important to maintain our healthy eyes... ___________________________________ SPAM REMOVED - maclhen - 4th Apr 10
| |
Now having said that, I’ve got to emphasize, they're low doses of radiation. It’s not enough to be dangerous and in fact, if you watch your television for several hours a day all year, you're getting less radiation than you would from a single medical x-ray and less radiation than you get from the radioactivity that’s just naturally within your body. So, it’s something that we can measure, but it’s not something that’s harmful.
Root vegetable cannon - DIY potato gun
Build yourself a root vegetable based cannon using just a biro, a hacksaw and a potato.
What you need
|
|
| |
A hacksaw |
|
A rod slightly narrower than the hole in the biro |
old biro
A potatoWhat to Do
First extract the inner part of your biro.
Then saw the ends off so you have a tube that is the same diameter all the way along.
Clean up the cuts using a pair of nail scissors. (It may help if you make the edges slightly conical).
Now jam each end of the biro about 1cm into the potato; so you get a lump of potato stuck in each end.
Point one end somewhere safe, and push the lump of potato in the other end down the tube, using the rod.
What may Happen
You should find that one of the lumps of potato fires off at an impressive speed.
What is going on?
The lumps of potato make a good airtight seal against the inside of the tube, because as they are jammed into the conical hole, they are compressed. This means that if you push one of the lumps along the tube, the gas between them is compressed, increasing its pressure.
The pressure increases until the force it exerts on the second lump of potato is high enough to overcome the friction that is holding it in the tube. As friction drops when something is moving (this is why it is often much harder to start pushing something than keep it going) there is now a very large pressure force on the potato, acting almost unopposed by friction, so the potato accelerates out of the tube very rapidly.
| As you push the lump of potato down the tube, you compress the air in the tube. |
| Eventually the pressure builds up enough to overcome friction, and the second lump is fired out. |
This is based on the the same principle as how toy spud guns work, but they use something more engineered to compress the air. Air guns also work in a similar way; pulling the trigger releases a large spring which pushes a piston down a cylinder. This compresses the air behind the bullet until it overcomes the friction holding it there, and then it fires down the barrel.
In fact, based on this same principle, there are designs for a gun used to fire projectiles into space. The prototype was called SHARP (Super High Altitude Research Project) and worked by using a methane-oxygen explosion to fire a piston down a tube. This then compressed hydrogen to enormous pressures, which forced the bullet/satellite up the barrel. Compared to current rocket technology, only a third of the rocket's weight would be taken up by the equipment used to project it, allowing it to get into low earth orbit far more efficiently than using present rocket technology.
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.