Naked Science Question and Answer and New Horizons

01 October 2006

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Answering all your cosmic conundrums this week are Drs Chris, Dave and Phil who discuss why blood is red, the size of the ozone hole, how to make magnets, the best way to get rid of excess mucus, and sticking with the gooey theme, Adam Summers discusses how some tarantulas keep a firm hold on the ground by producing sticky silk from their feet. Moving much further away from terra firma, New Horizons scientist Hal Weaver talks about the mission to Pluto, what they hope to find there and why the Kuiper Belt objects are so intriguing, and in Kitchen Science, Derek Thorne and Hugh Hunt carry out their own launch by throwing engineering textbooks high into the air.

In this episode

Human Surgery in Zero Gravity

Doctors lead by Frances Chief Surgeon Dominique Martin have become the first ever to perform surgery on a human in zero-g. The European Space Agency-backed experiment aimed to prove that zero-g surgery was possible in advance of preparing for long duration space missions. The operation took place on board a specially modified Airbus 300 plane that simulates weightlessness by rising and diving at just the right speeds so that the people onboard are actually in freefall within the plane. This is the same effect that causes your stomach to somersault when you go over a hump-back bridge and is the same technique used to film the Apollo 13 movie. The operation was to remove a benign tumour from a patient's arm and was a complete success. This surgery was chosen because it was relatively simple and would not involve too much bleeding. The operation was also easy to halt in case of problems. The next aim for the program is to test robotic 'surgeons' that would be remote controlled from the ground. If technology like this was fully developed it would allow a surgeon on Earth to perform emergency surgery on an astronaut on the space station or a future Moon base.

'FACE' ON MARS A FIGMENT OF IMAGINATION Many of you out there will be familiar with the image taken by the Viking 1 spacecraft that appears to show a giant face sculpted into the Landscape of Mars, but new image by the European Space Agency orbiter, Mars Express, have shed new light on the area. All sorts of conspiracy theories have used the iconic image as evidence that there was once a civilisation on Mars that constructed the huge human looking image and the area has formed the setting of numerous science fiction stories. However the new photos show that the face is actually a fairly ordinary looking hill. The eye sockets and mouth are depressions separated by a raised mound that forms the nose. However the new detailed images do not look at all artificial and instead show the hill as a fairly plain natural occurrence. The face interpretation probably comes from a combination of effects. Firstly the contrast was significantly enhanced on the original Viking images to allow scientists to more clearly see faint surface features. Secondly humans are very good at recognising faces, an essential ability that allows us to tell each other apart. Unfortunately this can allow our brain to be fooled into thinking that unrelated patterns are actually faces, as has been the case here on Mars.

Purrfect Pussy

The cat guaranteed to spare you sneezes and wheezes - a US company - Allerca - are marketing a cat which they say will not trigger allergies. The moggies are marketing at $4000 (US) and produce a different form of a genes called Feld1, which is responsible for triggering reactions in sufferers. In trials, blindfolded volunteers were exposed to the allergy-free cat, a regular cat and a furry dummy cat. They were then asked to keep a diary to document any allergy symptoms. The results suggested that the allergy-free cat, called Joshua, was less irritating to the volunteers than the regular cat, named Tiki. Allerca's founder, Simon Brodie, says that he he initially began by trying to engineer a low-allergy cat, but in the process of doing so stumbled upon three animals that naturally make a slightly different "wheeze-free" version of the Feld1 protein. "You could say we got lucky", he says. However, Allerca have yet to publish their work in a peer-reviewed journal so that it can be scrutinised by other scientists. As a result some researchers have expressed doubt over the findings, saying that Allerca should produce evidence that their cat's skin and hair do not bind to human antibodies. Responding to the critics, however, Brodie said "We don't have the data yet, but we do know the animals work. If these scientists are sceptical, and if they happen to be allergic themselves, I would say 'come and hold one of our cats'".

'Face on Mars' a Figment of Imagination

Many of you out there will be familiar with the image taken by the Viking 1 spacecraft that appears to show a giant face sculpted into the Landscape of Mars, but new image by the European Space Agency orbiter, Mars Express, have shed new light on the area. All sorts of conspiracy theories have used the iconic image as evidence that there was once a civilisation on Mars that constructed the huge human looking image and the area has formed the setting of numerous science fiction stories. However the new photos show that the face is actually a fairly ordinary looking hill. The eye sockets and mouth are depressions separated by a raised mound that forms the nose. However the new detailed images do not look at all artificial and instead show the hill as a fairly plain natural occurrence. The face interpretation probably comes from a combination of effects. Firstly the contrast was significantly enhanced on the original Viking images to allow scientists to more clearly see faint surface features. Secondly humans are very good at recognising faces, an essential ability that allows us to tell each other apart. Unfortunately this can allow our brain to be fooled into thinking that unrelated patterns are actually faces, as has been the case here on Mars.

What happens when you hurl your homework in the air?

This week Derek is with Professor Hugh Hunt from the University of Cambridge and three student volunteers from the Norwich School. They're going to be throwing books into the air and learning about the science of spin.

To do the experiment, you will need:

- A rectangular (preferably hardback) book

- An elastic band to hold the pages together 

How to do the experiment:

1 - Take the book and put the elastic band around it to keep the pages together. 

2 - Hold the book in your hands so that the book is flat and the spine is facing away from you. 

3 - Throw the book up into the air and make it spin so that the spine moves towards you and then away again. Catch the book and see if it looks any different. 

4 - Now hold the book so that it is flat between thepalms of your hands with the spine facing away from you. Spin the book again, aiming to make the spine come towards you and away again. Look again at the position of the book once you've caught it. (Don't worry if youcan't see any difference in stages 3 and 4!) 

5 - Now hold the book as though you were looking atthe cover ready to read it. The spine should be on the left hand side. Throw it up into the air and make itspin. What changes about the position of the book? How has the cover changed relative to how it was before you threw it?   

What's going on?

In steps 3 and 4, nothing particularly remarkable happens! They spin about the same axis all the way through and land in your hands in the same orientation.  However, when you throw it in step 5, it should have landed in pretty much the same way but rotated round 180 degrees. You will have noticed this because the front cover should be upside down. Anybody watching you throw the book will see that it starts going up normally and spinning but then does a flip when it gets to the top.  So what's happening?

When you throw it up into the air, the book starts spinning as you would like it to spin, but it doesn't last long! It turns out that spin about this particular axis is unstable, and doesn't like to spin in the way you would expect for very long. This makes the book start to tumble out of control. Once it's done this flip, it magically starts spinning nicely again, but the other way round. This means that, when you finally catch the book, it's lying in your hands upside down. 

This is all rather different to the other two ways of spinning the book. These two spin directions are what we call stable. You can think of this by imagining holding a pencil by its tip. If you hold the pencil so that the rubber is pointing downwards, it won't move. In fact, you could hold it like that for hours because gravity is forcing downwards and the direction is stable.

In contrast, if you try to balance a pencil on your finger tip with the rubber pointing upwards, the direction is unstable and the pencil falls down.  You can imagine that this pencil is a little bit like a pendulum. When it's swinging backwards and forwards down the bottom, then it's a stable situation. But if you imagine tipping it right up around 180 degrees, it wouldn't stay there for very long. It would swing down, go right the way round and come back to the top again.

So if it fell to the right, it comes back again from the left. Instabilities quite often involve moving away from where you started and coming back again the other way round. This is why the book turns 180 degrees from its original position. However, if you throw it again, the flip turns the book in the opposite direction and brings you back to the beginning. 

If you toss the book up high enough, it might do two flips. This will make it come back into your hands with the cover in the same orientation as before you threw it. 

These same spinning stabilities and instabilities can be seen in objects such as mobile phones because they're the same shape as books (one long axis, one medium axis and one short axis). Even a cat falling out of a tree uses the same principles to move itself around. 

 

- Science Update - Lizard Toes and Dance

The Naked Scientists spoke to Chelsea Wald and Bob Hirshon from AAAS, the science society

Science Update - Lizard Toes and Dance
with Chelsea Wald and Bob Hirshon from AAAS, the science society

Bob - This week on Science Update, we'll learn why top engineers are working long hours studying lizard toes. But first, if fighting and making up with your significant other sometimes feels like a highly choreographed dance, you'll probably identify with this report from Chelsea.

Chelsea - At least one killer whale couple has a way to kiss and make up, and others may, too. That's according to animal behaviourist Michael Noonan of Canisuis College and his student Cerrene Giordano. They studied a year's worth of video tape of one pair of captive killer whales and found eight incidents of aggression, in which the female chasing the male. After a cooling-off period, Noonan says the killer whales then began to swim along side - by-side, in a behaviour called echelon swimming.

Michael - And they don't just swim along side-by-side, their tail strokes stroke in synchrony, so they're swimming in what almost looks like a dance. It's beautiful to watch.

Chelsea - He says echelon swimming is a common behaviour among other captive and wild killer whales, and scientists believe it reinforces bonds between animals. He says only more research can show whether other whales use echelon swimming to make up after quarrels, but it's intriguing that the animals seem to have the capacity for reconciliation at all.

Michael - It's hard to name something that's more valuable in human behaviour than peacemaking. So it's particularly exciting to see suggestions of peacemaking in killer whales.

Chelsea - He adds that it's one of only a few known peacemaking behaviours outside the world of primates.

Bob - Thanks, Chelsea. In the states, a cartoon gecko is a well-known spokes animal for a car insurance company. But selling insurance isn't their only trick. Geckos are also marvels of engineering. That's because the surface of their toes is packed with millions of tiny, spatula - shaped hairs. These hairs create enough friction to allow the gecko to scamper effortlessly up smooth walls, and enough adhesion to hang its entire body weight from a single toe - and yet the hairs can release their grip just as quickly and easily as they stick. Electrical engineer and computer scientist Ron Fearing of the University of California at Berkeley is leading an effort to create artificial microfibres that act like gecko feet. Their current prototype packs 250 million hairs per square inch.

Ron - These hairs make intimate contact with glass. And they don't slip, it's very high friction. But it doesn't quite work like the gecko because if you try to pull it off, it pulls off really, really easily, actually much easier than the gecko pulls off.

Bob - He says their current material could provide good traction for tires and shoes. But the technology could also lead to other applications, from pain-free adhesive bandages to wall-climbing robots.

Chelsea - Thanks, Bob. That's all for this week. Next week we'll discuss some more cutting edge technologies-one that should prevent train derailments and another that should speed up biohazard detection. Until then, I'm Chelsea Wald.

Bob - And I'm Bob Hirshon, for AAAS, The Science Society. Back to you, Naked Scientists.

- New Horizons And Visiting Pluto

The Naked Scientists spoke to Dr Hal Weaver, Johns Hopkins University

New Horizons And Visiting Pluto
with Dr Hal Weaver, Johns Hopkins University

Chris - We're going to be joined this evening by Hal Weaver who's from the New Horizons mission, and he's joining us now from Johns Hopkins University over in the States. Why are you going to Pluto? What's the point of this?

Hal - It's been dramatic how our image of the solar system has changed over the last ten years. Pluto's been at the forefront of that new understanding. There's been a big controversy about whether or not Pluto is a planet, but it's definitely something called a Kuiper Belt object. This is a new region just outside Neptune's orbit and it was just discovered in 1992. We now know of roughly 1000 objects out there and it's a whole new region of the solar system that hasn't been explored yet; a region that we're calling the realm of the icy dwarfs. Pluto is the prototype of those objects.

Chris - So what do we think is out there, Hal? What are these objects like and why are they worth studying?

Hal - They're worth studying for a number of reasons. One is that because they are so far away from the sun and outside of Neptune's orbit most of the time, they've always been cold since the time that they formed roughly 4.6 billion years ago. As you know, one of the best ways to conserve material is to keep it in a deep freeze. That's exactly what's been done with these objects. They've got a lot of ice and the molecules that they have retained over these last 4.6 billion years basically give us a window back to the time of the formation of the solar system. So by studying these objects now we have a much better insight into what's happening in the early solar system in that region of the solar system. This is in comparison to observing the Earth or other planets, where these objects have had so much evolution over the age of the solar system.

Chris - How long is it going to take New Horizons to reach Pluto? It left in what, February of this year wasn't it?

Hal - It was January the 19th of this year that we took off. We went screaming off the surface of the Earth; it was the fastest spacecraft ever launched going at about 36 000 miles per hour. But even going at those kinds of speeds it's going to take nine and a half years to get to Pluto because Pluto is so far away. It's roughly 30 times further from the Sun than the Earth is. So even though we had the most powerful rockets available and had a very favourable launch, it's going to take a long time. We're heading first of all towards Jupiter and one of the big reasons for going by Jupiter is to get gravity assistance. We're going to get a sling shot effect because Jupiter is so massive, and is by far the largest planet in the solar system with a mass of 320 times that of the Earth. The most important objective of our Jupiter encounter is to hit a little key hole in space; a little spot near Jupiter that will propel us on towards Pluto and cut off three to five years of our travel time and increases our speed by about 20%. But still, it's going to take about nine and a half years to get to Pluto. We know now that we're going to arrive on July 14th 2014.

Chris - How do you actually know that the probe is a) going to survive the journey, and b) be able to operate under those extremes of temperature? It must be about minus 200 degrees Celsius out there near Pluto. How's it going to operate?

Hal - Yeah that's right. There are very harsh conditions out there. But our spacecraft are actually nice and toasty; it's almost like a thermos flask. We have multilayer insulation wrapped around the entire spacecraft and just from the heat generated by the electronics, we generate enough heat to keep all the instruments, the spacecraft body and the telescope and so forth at roughly room temperature even when they're out by Pluto.

Chris - So what sort of science will you be doing at Pluto? In what way will you be interrogating that part of the solar system with the probe?

Hal - There are basically some questions that we want to address that are just too hard to do remotely. We are so far away from Pluto, so first of all we want to know: what does it look like in detail? The Hubble space telescope is the most fantastic space observatory available to us here on Earth, but it can barely resolve Pluto. It's done some magnificent imaging of Pluto but even with Hubble, it looks like a bunch of about ten pixels across. All you can tell is that there are some very bright regions and some very dark regions but it's very hard to tell what's going on. Why are these regions bright and why are they dark? We'll do thousands of times better than that by flying the spacecraft by.

Chris - And when you're out there, how long will it take a message or any of this data you're collecting to get back to Earth each time?

Hal - It's amazing. It turns out that from Pluto it takes four and a half hours for the light to reach the Earth. So the round trip will take about nine hours.

Chris - So it's a long old time. Once you've got to Pluto, will you carry on a go beyond the orbit of Pluto and keep exploring?

Hal - That's exactly right. What we're hoping to do is not to stop at Pluto but continue plunging into this region called the Kuiper Belt. As long as everything is still working then, we have a very good chance, we estimate something like 95% probability, that we'll be able to encounter another small Kuiper Belt object. Even with Pluto, we just discovered a year and a half ago two more satellites that Pluto has besides Charon, the one that was discovered in 1978. We have two more mini satellites; our own mini solar system out at Pluto, so effectively we have four Kuiper Belt objects to look at for the price of one by going past Pluto. The neat thing is that we have one of the largest members of that class and the smallest satellites in that system, and plus we hope to encounter more of the small Kuiper Belt objects to see whether they are like the objects of the Pluto system or very different.

- Tarantulas With Sticky Feet

The Naked Scientists spoke to Professor Adam Summers, University of California Irvine

Tarantulas With Sticky Feet
with Professor Adam Summers, University of California Irvine

Chris - Now if you're at all arachnophobia, cover your ears because Adam Summers is from the University of California Irvine and he's got a very sticky story for us about big spiders.

Adam - We've found that tarantula spiders, at least one species of them, produces silk with their toes. So they actually are producing the same sort of silk that spiders produce to make webs, except that instead of producing it out of their spinnerettes, which are on the back end of the animal, what's called the opisthosoma or the abdomen, they are producing it out of those eight little legs that are up on the front end. And, of course, they're tarantula spiders so there's nothing really little about them.

Chris - But why would they want to do that. Why do they need the silk to come out of their feet?

Adam - Tarantula spiders are terrestrial. They run around on the ground and we suspect that this silk is used to increase both friction and adhesion with their toes. Spiders have a really well known dry adhesive system that's quite similar to the gecko toe, but that doesn't always work and so having some sticky silk that comes out can give them a little more traction. And remember, these are great big spiders and they don't have a very well armoured exoskeleton, so if they fall, they're in real trouble.

Chris - So the theory would be that they, first of all, glue themselves to a surface and then as they move along, they're laying down a line that can essentially be a prevention to stop them falling.

Adam - Well no, not quite. So what you've just done is given a very nice description of what's called drag line silk and most true spiders will lay down a drag line. Every step they take they glue down a little bit of silk behind them and if you knock them off a table or something, they'll just hang by this thread. That's not what's going on here. These threads are unbelievably short. It was only through, basically, happenstance that we managed to visualise them at all. They are on the order of one or two millimetres long coming out of the foot, and so they are really only visible if you're looking at the footprint that's been left behind in the event that the spider skids its foot a little bit.

Chris - Is that what you did to see them?

Adam - Well, we had a very lucky thing happen. One of the authors on the paper was in charge of getting spiders to walk on glass and we were then going to look at the footprints. And one day he sort of took a longer break than usual and left the spiders on a tilted piece of glass. When he came back, these spiders, which don't like to climb on tilted glass, and so they sort of freeze and don't move, the spider had slipped backwards and as it slipped backwards. You could actually see this little bit of silk at the end of each foot, and once we'd seen that silk, we knew how to get it and how to visualise it. So we were able to see it when they were walking normally and able to put it under the scanning electron microscope and visualise exactly what the fibres themselves looked like. We also subjected them to some chemical tests and see that they are just as difficult to dissolve as regular spider's silk.

Chris - So what came first, actually the ability to spin silk from the abdomen or the ability to spin silk from the feet, from an evolutionary point of view?

Adam - Therein lies the really interesting question and Cheryl Hyashi, who's at the University of California at Riverside and is a co-author on this paper, she uses genetic techniques to try and understand which of two scenarios happen. The spinnerettes, which make silk in all spiders, are thought to be vestigial limbs. Did those limbs have silk because all arthropod limbs have silk? Or, did the limbs gain the ability to produce silk because the hardware for producing it was already in the genome and it was being expressed in the spinnerettes?

Chris - Adam Summers there describing how tarantula's produce silk from the tips of their toes.

- How to stop my body making mucus?

Can you please tell me how to stop my body making mucus? I've had dysfunctional Eustachian tubes for seven months, and although they're s...

How to stop my body making mucus?

Mucus is very important, especially in your lungs. We did an experiment with this on TV a while ago. Mucus catches all the dust and bits in the air. If you didn't have mucus, all the tiny bits in the air would be carried deep into your lungs, which can do all sorts of damage, especially if it's toxic. As the mucus is sticky, it catches all these bits and you can either bring it up as phlegm or it runs out of your nose, taking all the poisonous nasty stuff with it. The reason that Dee probably has this problem could be down to allergy or some other inflammatory process going on. But usually it's down to something that you're breathing in that's making your airways inflamed. The reaction to an inflammation is to make lots of mucus. How do you get rid of it? Well there's one way to knock it down, which is to take some steroids like you've done. That will help to stop the inflammation quite effectively. The other way is to take some antihistamines. These are good because they stop histamine, which is a class of cells produced by mast cells. Mast cells are coated with an antibody called IgE that recognises allergy-provoking substances. When the allergy-provoking substance binds onto the IgE on the mast cell, it tells the mast cell to pump out this histamine, which is an inflammatory substance that makes you have sticky eyes, itchy eyes and a blocked up nose. If you take antihistamines then you block the action of the histamine before it has a chance to get going.

- What are magnets made of?

What are magnets made out of and how are they made?

What are magnets made of?

Magnets are very useful things: you can stick things to fridges with them and they're very important in things like hard disk drives in your computer. You can even make levitating trains with them. But how do you make a magnet? Inside a metal like iron there are lots of tiny little magnets [called dipoles]; to start off with, they're all pointing in different directions. It's like if you had a load of magnets inside a big bucket: they'd all be pointing in a random way. What you need to do to make them into a magnet is to line up all those tiny magnets [dipoles]. The way you do it is to heat up the material, which allows all the mini magnets to move around. You then put a big magnetic field around it. This causes all the little magnet dipoles to line up, as you may have seen compasses do in a magnetic field. If you then cool down the material in that magnetic field, the dipoles will all be lined up and you'll have what you think of as a permanent magnet. Of the elements in the periodic table, iron, nickel, aluminium and cobolt can be made into magnets. These latter elements are referred to as al-ni-co. They have what is called a high coercivity, which means that, once magnetised, they have a strong tendency to remain magnetic.

Some of the rare Earth elements are also used to make magnets. These include neodymium and samarium.

- Is the ozone hole shrinking?

Could you tell me if the ozone hole is now getting smaller since CFCs have been banned?

Is the ozone hole shrinking?

It's not actually getting any smaller yet but it's stopped getting any bigger, which kind of amounts to the same thing. What we see is a lag between the CFCs or chlorofluorocarbons, which are implicated in causing the ozone hole, going into the atmosphere. Then they react over Antarctica and damage ozone and make the hole bigger. If you see the hole not getting any bigger then that means that the reaction causing it must be slowing down, and at the same time ozone's continuously being remade. So the two processes must now be in balance, meaning that if it keeps on slowing down, within the next few years the hole should start to shrink a little bit. But let's not be too over-confident or complacent about this because the ozone hole is about the size of the American continent.

- Why can I hear the other side of a cassette?

I know cassette tapes are virtually obsolete, but I have a question about them. Very often when I'm listening to my Harry Potter audio bo...

Why can I hear the other side of a cassette?

The way a cassette works in the first place is that you have a big long strip of iron and when you apply a magnetic field to it, it gets magnetised. That's how you record things onto it. The varying magnetisation can then be converted into vibrations and you hear that as sound. The way that a double-sided cassette works is that when it's one way up it reads information from the bottom of the cassette and when you turn it over it reads it from the top of the cassette. So you have two strips: one at the top and one at the bottom with different information on it. So what's probably happening when you're hearing the muffled sounds is maybe the sensor that's reading the magnetic field is a bit too close to the middle and so you're picking up some of the other side of the tape, probably backwards.

Why is blood red?

The reason blood is red is because it's got iron in it. If you look down a microscope at blood, what you'll see are thousands of tiny little red cells that are referred to as bi-concave discs. If you look at them from the side, they look like a number eight and that's because they've got a thick ring round the edge and a flattened centre, a bit like a doughnut. They're crammed with a substance called haemoglobin, and haemoglobin is what carries oxygen around the body. Haemoglobin's a protein - in fact it's four proteins stuck together - and in the centres of each of those four proteins there is an iron (Fe) atom, which gives haemoglobin its red hue. But blood isn't exclusively red. Some drugs can bind to haemoglobin and alter the chemistry of the iron atom, causing the blood to change colour. In fact, a sulphur-containing migraine treatment called sumatriptan can do this in some people, making their blood go green.

Also, many animals have a different form of the haemoglobin protein with a different metal at the centre in place of the iron, which can also alter the colour. The horseshoe crab, for instance, has blue blood because it uses copper (Cu) instead of iron. And the real hippies of the haemoglobin world are a kind of marine annelid worm. It actually has purple blood!

- Can I have a leech for a pet?

Can I have a leech for a pet? I am allowed to buy one? If so, where can I buy one?

Can I have a leech for a pet?

I've picked some up by wading in streams occasionally. If you wade around then they should find you! Medical companies do actually supply and you can use them for medical purposes. In the old days people used to blood let because they thought that it was good for people. But in fact leeches are very useful because they have venom that stops clotting. It's called hirudin and it's a tiny protein. When they bite you they inject it and it keeps the blood from clotting so they can keep drinking. Surgeons love them because if you have a bit of plastic surgery when a part of your body has been severed such as a finger or piece of ear, it's very easy to reattach things like arteries because they're quite large and chunky. But the veins are quite floppy, difficult to identify and it's very difficult to reconnect them, so blood can get into your tissue quite easily but not back out again. This means that the tissue can end up starving because the circulation can't go all the way through. So what scientists and doctors have found is that if they attach leeches around the site where you want to stitch something back together, you can keep pulling to blood out. As long as you keep a nice flow of blood coming in, then the tissue revitalises and the vessels grow back together. When the leech gets full, it just drops off. There are companies that will supply medicinal leeches but they're usually used by doctors, not members of the general public.

- Why do some senses degrade sooner than others?

Is it true that some of our senses degenerate and that some of them are more susceptible to damage than others? We see kids wearing glass...

Why do some senses degrade sooner than others?

With glasses, there's definitely some kind of environmental effect there. If you spend all your life studying, then you're much more likely to end up with short sightedness. I can see that both Phil and I have glasses on today! In Singapore where there's a very strong emphasis on education from a very early age and lots of people spend lots of time studying, the rates of short sightedness have gone through the roof. There's a lot to be said for people going out onto the sports field and learning to focus their vision in the distance. When you're young and you're body is developing and growing, if you do a lot of close work you don't develop a capacity to see well into the distance. But in terms of degeneration, just because you wear glasses doesn't mean that your eyes are actually degenerating; it just means that they're not working as effectively as they could. With going deaf, on the other hand, there's actually a problem with part of the ear that turns sound waves into electrical signals. That's because over time the tiny nerve cells that do that job get damaged by loud noises, the effects of ageing and the effects of damaging chemicals in the blood stream. Once they're lost, you can't replace them, which is why you get a progressive deafness.

- Who would win a fight between a hippo and a polar bear?

Who would win a fight between a hippo and a polar bear?

Who would win a fight between a hippo and a polar bear?

I think that polar bears are a lot faster than hippos, so that element of nimbleness would give it a great advantage. Although I guess if they got close enough, a hippo is a really vicious animal. I think that more people are killed by hippos in Africa than they are by lions and tigers and actual carnivores.

- Why do I sneeze when I stare at the sun?

How come I sneeze when I stare at the sun in the morning?

Why do I sneeze when I stare at the sun?

That is called the photic sneeze reflex and it's something that's a big problem for people who want to be in the RAF or in the US flying corps. One in four people has this, it's thought to be genetic and it tends to run in families. It's seems to be that when you have bright light going into your eyes, in those people who are susceptible, the light in some way triggers you to want to sneeze. We used to think that the light made your eyes water and the water ran down your nose, making it tickle. But it happens far too quickly for that so we think that it's actually some mis-wiring in the back of the brain that triggers your sneezing centre.

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