Why is it that some smells disappear with continued smelling? Tim Chiles

Kat -  The answer here is something to do with adaptation and desensitisation.  It’s the same reason why you’re not sitting there going, ‘Oh gosh, I’m not wearing clothes! Oh, I’m sitting on a seat!’ all the time.  If that happened, if our nerves responded to every stimulus we’re getting all the time we would just be overwhelmed and wouldn’t know what to do.  What happens if you’re sniffing vinegar or something with a really strong smell?  It goes under your nose, up into your nose and it activates something called olfactory neurons.  These are basically smelling nerve cells up in your nose and they send a signal to your brain that says, ‘This is a really strong smell, this is what it smells like.’  The signals that are being sent by those neurons are in the form of chemicals, little chemical messengers.  They kinda get worn out.  They run out of chemicals in these cells.  Something called desensitisation happens.  You stop being able to smell the smell.  This is very important because say if you’re – if you think back to our ancestors sitting around in the jungle or in their cave – you want to spot new things happening to you.  You don’t need need to know about what’s going on that’s already happening to you.  You want to spot new stuff.  Something like a very strong smell you need to spot it when it’s new and it’s happening so it can be over the level of noise that’s going on around you.  What happens if you’re smelling a strong smell after a while you’ll stop smelling it, basically.  Anyone who’s lived with boys and particularly whiffy toilet habits will know this.

Chris -  The evidence is that men and women make equal amounts of smells, equally often during the day.

Kat -  Yeah, yeah...

September 2008

How does a Newton’s Cradle work? In school I was taught that the mass X velocity = mass X velocity. In other words, one ball in means one ball out. The teacher pulled back two balls and let go. The two balls at the other end of the contraption went up about the same distance as the first two balls. Why didn’t just one ball fly off at twice the speed? Joe and Brian

Dave -  Newton’s cradle is a whole series of collisions.  You’re taking a really bouncy metal ball, it’s very hard steel ball and bouncing it into a row of them from one end and crashing into it.  In this kind of collision there’s two things which are conserved, which have the same amount at the end that you had at the beginning.  One is energy that you were talking about before.  That’s ½ x mass x (velocity) squared.  The other one’s something called momentum which is your mass X velocity. You've got one ball dropping into it with a mass and a velocity you will have the same mass and velocity by having one ball coming out with the same energy and the same momentum.  With two balls with the same amount of energy then they’d actually be moving less than half the speed.  So they’d have less than the same amount of momentum you’d put in.  The only solution is to have the same amount of balls coming out as went in.

Chris -  Is it not also that there’s a little tiny delay between one ball hitting and the next ball hitting?  The same when you get two separate collisions throwing off two separate balls.  When you go two balls in you get two balls out because it spits one ball and then the next ball out.

Dave - That would be another way of looking at it.  Physics can be looked at in different ways.

September 2008

The molecules in a single drop of water diluted evenly in the Earth’s oceans would result in the density of one molecule per litre of sea water. In other words, if you made one little drop of water go into the sea somewhere, given enough time, there’s enough molecules in one drop to spread out across the whole of the Earth’s oceans so there was one molecule per litre. Eric Moser and Robert Moser

This is their maths: There are about 24,000 droplets in one litre. That gives you a droplet volume of about 0.03cm cubed. The relative molecular mass of water is 18g per mole. A mole is the number of molecules, it’s the mass in grams of the molecules in one mole. You need that to calculate the next bit of the equation. In one litre there must be 1000/18 moles. We know from Avogadro’s  constant there are 6.022 X 10 to the 23 molecules in a mole of something. That means that in a litre of water there must be 1000/18 X 6.022 X 10 to the power of 23 molecules in a litre. That means per droplet you have to divide that number by 24,000 because there are 24,000 droplets in a litre. That means there must be 1.39 X 10 to the 21 molecules of water in an individual droplet of water which is an amazing number of molecules.

The volume of the Earth’s oceans is 1.37 X 10 to the 9 cubic km. That’s a reasonably well-understood figure. If you need to convert that into m cubed you have to times it by 1000 cubed because there’s a thousand m in a km. That’s 10 to the power of 9. To turn that into litres you’ve got to times it by 1000 cubed again. So that’s 10 to the power of 12. That means that on Earth there are 1.37 X 10 to the 21 litres. That’s nearly the same number as there are molecules in the droplet of water. If you put one into the other you have almost one molecule of water per litre of water on Earth.

September 2008

You have to spend 10-20 minutes in the sun to make vitamin D. Since I moved to Australia I’ve also been told how important it is to wear sun block. My question is, does wearing sun block affect the rate that vitamin D gets formed at? Is there no difference? Alan, Sydney; Sean Maul, Canada

Kat -  Yes it does.  For most healthy people you should be thinking about wearing the sun cream rather than worrying about your vitamin D.  The simple reason is this: sun block does block ultraviolet radiation which is the stuff that helps you make vitamin D.  It’s also the stuff that damages your skin and gives you skin cancer.  This is why in somewhere hot and sunny like Australia it’s very highly recommended you protect yourself in that way.  You do only need a few minutes of sun exposure to make enough vitamin D.  It’s certainly less than the time it takes for your skin to go red or to burn.  It’s really hard to be prescriptive about how long you need because it’s different for every person.  Someone who’s very fair like me, I burn really easily.  I’d probably need much less time in the sun that someone with much darker skin.  Also sun block and sun screen are not perfect: they’re not this magic shield against the sun.  People don’t use them in the way that manufacturers recommend.  They don’t put enough on, they don’t apply it regularly enough.  You’ll know if your skin burns easily that you can put some on and still get burnt.  There’s some ultraviolet getting through.  We know there are some studies that show we do need vitamin D to protect us from things like cancer but you can certainly get more than enough vitamin D with casual exposure to the sun: popping to the shops with your sleeves up.  If you’re going to go serious exposure to the sun then definitely protect yourself.

September 2008

I had an L-shaped stone, threw it in the water and but all the ripples were circular. Why is that? Mark Wolford

Chris -  It’s a common thing, isn’t it?  When you throw things in you think why do I get this ripple going out?  The answer is that when you first throw a stick into water you will get a stick-shaped initial ripple but as the ripples spread out you’ll get the L-shaped bit going out a bit but then what about the spaces?  What about the bits in between?  They’ll get filled in with a curve.  Eventually as it gets farther and farther out you’ll end up with something that is predominantly curve with very little of the original shape left behind.  It looks to all intents and purposes like a giant circle.  The contribution of the original shape is absolutely tiny.  That is why it does that interesting morphing thing into a circle from something which was originally a different shape.

Dave -  So all the ripples are going outwards at the same speed and they start off in different positions but after a couple of seconds those different positions they start on doesn’t make much of a difference.

Chris - In the grand scheme of things, no.

September 2008

You discussed pressurising air in the aeroplane. Listeners were saying they’d been on planes and their ears had popped. Why do they pressurise the plane to only 8000 feet? Why don’t they pressurise it to atmospheric pressure? Colin

Dave -  They did start doing this on the first jet airliner which was the comet. They also had lovely square windows and the aeroplane kept getting pumped up to atmospheric pressure and kept rising high up in the atmosphere. It got a big pressure on the structure coming down again and going up again. That stress on the airframe slowly built up cracks which got longer and longer until the cracks ran between all the windows and it opened up like opening postage stamps.  They actually lost several planes due to this.  Since that they’ve made the windows much more curved and they’ve also started not pressurising the plane all the way up so you’re putting less stress on it. You could design a plane which would survive the high pressure but it would involve making them much heavier than you’d want to and they want to make it as cheap as possible.

Chris -  You’re carting loads more weight into the air which is costing you more fuel and in these days of high fuel prices that’s a bad thing.

Dave -  The other thing is that to compress that air - you need more air because you’re constantly taking more air and compressing it from a low pressure to a high pressure inside the plane - takes lots of energy and more fuel

Chris - Graham.d on our forum calculated that the actual weight of the molecules themselves would contribute an extra 250kg. Basically an average British large person or several people my weight travelling for free if you don’t pressurise to atmospheric sea level pressure all the way up there. That’s pretty interesting.

September 2008

How do you age a palm tree because they don’t have rings? Sofia

Kat -  This is a really interesting one and it’s very tough to date a palm tree because they don’t have rings.  Especially it applies to plants such as cacti and yukkas that don’t have that ring structure.  In the case of really old palms you also can’t really radio carbon date them.  This works for trees because they have the same consistent heartwood all their lives but this doesn’t really happen for palms.  Some botanists use techniques which include counting leaf scars.   Palm trees make new leaves, leaves fall off.  You can count how many scars there are and multiply it by the average time taken to grow new leaves.  It’s not great.  Really the best technique is to look at historical information.  If you can find out when an area was colonised by humans if the tree’s not a native species they probably brought it with them.  You can look at old written records, historical records, paintings, photos.  There’s not really a very good way to age a palm tree.

September 2008

Why do crisp packets and sweet wrappers make so much noise? Vince Magno

Dave - Well, I think this is quite a complicated one.  I think one of the things is they’re big sheets so if you move them like this piece of paper any movements they make are very well connected to the air because they’ve got a large area.  If they move a bit then the air has to move.  The vibrations in them get transferred to air very easily.  Also if you take a piece of paper of a crisp packet and crumple it, it doesn’t just fold neatly and you get nice even folds.  You tend to get complicated folds which actually become quite strong.  When you break those you actually release a load of energy which vibrates everything and connects to the air.  The air vibrates well and makes a lot of noise.

September 2008

Is it true that you can re-grow the liver after chopping a bit off? Could that be the answer for the thousands of people that are waiting? We could turn the population into liver donors. Jeremy Langdon

Kat -  It’s true that the liver does grow back.  It does this amazing regenerative potential.  You can pretty much cut away half of someone’s liver and it will grow back again.  It does sound like a fantastic idea for transplant patients but sadly you will still have the problem of tissue rejection.  You have to very, very carefully match it.  Some people do offer to act as living donors.  You can donate kidneys, you can donate livers to people you’re very closely related to.  You’re likely to have a very similar tissue type but obviously trying to remove part of someone’s liver is pretty major surgery and it’s not something that you’d want to go into lightly.  Really the problem of the thousands of people waiting for transplants is really to get more people to sign up for the organ donor register.

Chris -  I think another problem with the liver is that if you do take away a big chunk of the liver, although the cells might have the capacity to replace lost cells and make up the cell numbers there won’t be the architecture, the structure there for the cells to hang around or to be strung from in order to make a new liver.  Although you could make the cells back you couldn’t make the same shape and structure.  It would be very difficult for it to repair itself like that so I think there’s more to it than just -

Kat - It will grow back.  The liver will actually grow back a couple of weeks after removing it.  It’s really phenomenal. In the case of cancer patients you can remove 50-60% of someone’s liver and it will grow back.

September 2008

Could viruses be engineered to attack cancer cells selectively? Michael

Chris -  They have been.  This is a really hot area because viruses are very bad for cells.  They basically turn cells into virus factories.  They will go into the cell.  They will grow very fast in the cell, turning it into a virus factory and kill the cell in the process.  Researchers are thinking if we can exploit that then we might have a way of making the virus attack just a cancer and kill it.  There have been a number of approaches to doing this.  Up in Scotland Moira Brown who’s been on this programme has been working on a strain of Herpes Simplex virus, the virus that causes cold sores, for example.  She’s found a mutant form of the virus which has damage to a gene called gamma 34.5 and this gene, if you switch it off, stops the virus growing in brain tissue.  What this means is that if you have a brain tumour you could inject the cancer with this virus.  Because the brain tumour is very fast growing cells the virus can still grow in those cells.  It will replicate making more virus which will go into more cancer cells and kill those cells which will go into more cancer cells.  The whole thing grows until it runs out of cancer cells.  As soon as it hits the healthy tissue interface where the healthy brain tissue is again it switches off.  This is viewed as a very powerful way to very selectively weed out the tumour cells that are growing invasively between the healthy tissue without actually having to do radical damage with a scalpel to someone’s brain.

Dave - Would you have to have a different virus for each kind of cancer or would you be able to get one which would get the most?

Chris - Not necessarily but the likelihood is there’s going to be horses for courses.  Some viruses naturally have a tropism, a tendency to go into certain cells types.  HIV for example, tends to home in on white blood cells.  If you wanted to target a certain kind of disease of those white blood cells you might use a virus to start with which is very good at homing in on certain types of tissue.  Other times it’s been a case of modifying the virus so that the receptors or docking stations on the surface of the cell are slightly different so that they will then go onto certain types of cells.  It’s a work in progress, isn’t it?

Kat -  There’s lots of research that’s going on funded by Cancer Research UK.  Ovarian cancer is a cancer that’s really ripe for virus treatment because mostly ovarian cancer tends to stay inside the tummy, in the same place.  You can kind of inject the virus in there and it will get rid of all the cancer cells.  There’s some clinical trials that are currently underway.

September 2008

I was just wondering, is there any radiation that would come from a glow-in-the-dark watch that would be harmful to the wearer? Sandra, Melbourne

Philip Clark, University of Edinburgh, Experimental Particle Physics Group:

It depends very much on the type of dial that you’re considering.  By far the most common watch that you come across that’s glow in the dark is called a phosphorescent watch.  Essentially the watch is coated in a paint which absorbs light and then re-emits it.  These watches are completely harmless. 

The second type of watch is called a tritium watch.  The modern way to do this is you have the same phosphorescent paint but this time it’s mixed with small tubes filled with tritium.  Tritium is radioactive and emits beta particles.  These have the same effect of exciting the phosphorescent paint.  This time tritium has got a half-life of 12 years.  The beta particles that are emitted are not very energetic so if anything they couldn’t even penetrate the outermost skin layer. 

The third watch I’d like to mention is a radium watch.  They have very much the same design but this time instead of tritium they’re mixed with radium.  The half-life is sixteen hundred years.  However, they may not seem to be as radioactive because the phosphor in the paint gets eaten up by the radium.  I’ve got a small demonstration here so I’ve got an old watch that I’m going to hold a Geiger counter to.  If I turn the Geiger counter on you’ll hear it clicking:

<click>

That’s when I hold it slightly close to the watch.  If I hold it really close to the watch:

<much more rapid series of clicks>

And the take it away from the watch then the background count – you can hear the occasional count just now is much lower than if you hold it closer to the watch.  These watches are extremely radioactive.  However they’re still not too harmful unless you were to break the watch and inhale it or somehow ingest the watch.

September 2008

If you happen to have your jugular artery or femoral artery cut how long would it take for you to bleed out? I was having a heated discussion with someone about it. He says 36 hours. I say he’s nuts, it would just be a few minutes. Who’s right? Marie

Kat -  I think you are.  If you have an injury to a major artery you could be dead with a matter of minute from loss of blood.  This obviously happens all the time in serious accidents.  Very nasty stuff.  Basically you just have this massive drop in blood pressure.  You can’t supply blood to your brain, you can’t supply blood to your heart.  You conk out pretty quickly.  If it’s in terms of getting all the blood out of you it probably wouldn’t take that long either.  It’s probably good to get all the blood out of normal people anyway.

Chris -  You’ve got a cardiac output of five litres a minute.  In other words your aorta, your main blood vessel, has got 5 litres of blood running through it every minute.  Your circulating volume, the amount of blood in your body is 5 litres.  At most if you cut someone’s aorta, if they had an aneurism that burst they could potentially lose all the blood in their body in one minute.

Kat -  Yep, you’d be in trouble.  Also bleeding over 36 hours is extremely unlikely unless you had some condition like haemophilia which meant you couldn’t clot.

September 2008

If light has no mass, how can a black hole capture it? Sri Adibhatla Soma Sekhar

Dave -  Light has no mass but it is affected by the shape of space.  What Einstein worked out in general relativity was if you have a very large mass it distorts the shape of space.  If you shine light across a curved piece of space it will get bent by it.  A black hole is basically so heavy that it bends space so much that light will get bent a bit like a lens and come straight back into the black hole again.

Chris -  That’s why they look black, because there’s no light coming back out.

September 2008

What makes our hair turn grey? Is it true that things like fright and stress can make that happen? Ian, Sprowston

Chris -  The reason that hair goes grey is naturally it’s a white colour.  That’s the colour of the protein, keratin, that hair is made from.  You have in the hair follicle which is a special ring of stem cells in the surface of your head, under your arms and other areas of your body cells called melanocytes.  These make melanin, the same stuff that gives you a sun tan when you go out in the sun.  Melanocytes add to the hair melanin.  They add different chemical forms of melanin: pheomelanin and eumelanin.  This is a dark colour.  Depending on what ratios you put in and how much is in the hair the hair goes darker.  If you have, for some reason, a loss of those melanocytes  they stop making melanin and the hair goes back to its natural white colour.  What happens is as we age the melanocytes burn out.  They stop making this particular chemical and as a result you go grey.  As to whether it goes grey overnight I think you looked into this, Kat.  The answer was, it’s more likely that people’s hair might fall out and then it comes back white because they were going to go grey anyway.

Kat - Exactly it’s very unlikely to go white over such a short length of time.

September 2008