Can we harness the power of lightning?

How much water do we lose in a day? What's the best way to drink a Scotch whisky? Can we harness the power of lightning? Can things move faster than the speed of light? Are things that burn totally destroyed? Could a cable run from Earth to space to generate energy? Would exercise just before bed help weight loss? Can we have solar panels instead of windows? Plus, can circumcision protect against HIV? Chris Smith joins Eusebius McKaiser to answer your science questions...

Eusebius - Very well thank you. And today's story, a very important one particularly in this part of the world. A story in the world of science related to circumcision.

Chris - Yes. This is one of the follow up studies which build on the discovery, about 10 years ago, that circumcision in men can dramatically reduce the risk of picking up HIV. The latest data comes from Zimbabwe where there's been a number of initiatives to increase the rates of circumcision in order to protect people. And what they've now done is to go back and say what sort of a dent is this making in the HIV epidemic in that country. So this is a paper in the journal PLOS ONE. Jessica McGillion is the lead author and the second author is John Stover whom we spoke to this week. About a million circumcisions have been done in young men between about the ages of 10 and 49. And what the researchers have done is to go into the country to collect data from people to look at behaviours. They've asked about infection rates, they've asked about circumcision rates, and they've used this data to calibrate a mathematical model to then look at the impact of this initiative in order to ask the question "actually, is this bearing fruit is this making a difference to HIV infection rates?" And what John Stover told us this week is that of the million people that have been circumcised, this has immediately led to the prevention of about 80,000 cases of HIV in the country. This will grow over the next 10 to 15 years to about half a million cases of HIV prevented because most of the people who've undergone the procedure so far were not sexually active because they were young. And so as they go into the bracket where they begin to become sexually active, then obviously the protection will continue later in their lives. So they're arguing that with their target of 80 to 90 percent penetration rate of the procedure, if they can get to an 80 percent rate, then actually this will return millions of people who will be prevented from catching HIV over the time so they think it's very worthwhile. And in terms of cost benefit actually the cost of running the circumcision program is more than offset by the savings of not having to give people antiretroviral drugs because they haven't caught HIV. The level of protection is between 60 and 80 per cent for the men who get circumcised and about 50 percent for the partners of those men.

Eusebius - Stunning. Let's talk to Brigette. Good morning Brigette. Welcome to the show.

布里吉特-我想问多少钱fluid an adult should have in 24 hours and whether coffee and tea count and whether tall people, short people, fat people all need the same amount of fluid?

Eusebius - A very good question. I want to tag onto that one Chris and ask whether one can have too much as well?

Chris - It's interesting she didn't say anything about wine or beer. You know, an enormous level of self-restraint Bridget. The answer is you need to replace what you're losing. Humans are extremely good at controlling their water losses. Not as good as a tiny mouse that's adapted to live in a desert, but we're still extremely good. We have very good kidneys which are capable of scavenging back most of the water. The water we are obliged to lose, these are called insensible losses, is lost in the body in a range of ways. We lose water in the obvious way through urine. We also lose water from our breath, so you lose about half a litre of water just from breathing. There's also evaporation from sweating and in a hot climate you can lose up to five litres an hour from sweating. So its very variable and it will depend, the amount of water a person loses, on where they're living and what they're doing, and if they can afford to lose water. Because the body, as soon as it becomes dehydrated, will start scavenging back water from all the sources it possibly can. So to be healthy you need one or two litres of water, probably about two litres of water a day minimum really. Less than that you can cope with. More than that your body or just get rid of it. But if you overdo it and you outpace the ability of the kidneys to throw water away then you're in trouble as well because if you put too much water in the body you dilute your blood down too much, water leaches out into your tissues and this can make your brain swell.

And people who for instance have gone to rock concerts and nightclubs and got too hot, drunk too much water to compensate often because they've been on drugs that have given them extra bursts of energy and made them dance too fast for example, they get brain swelling and this can cause fitting and sometimes it's fatal, so you can overdo it. It's better to just put back in what you've lost, and any source of fluid is a good source of fluid within reason. Alcohol: bit different because alcohol is itself a diuretic, but tea coffee, juices they're all water based. Most of them 99 plus percent water so it's absolutely fine and it will rehydrate you beautifully. Alcohol - anything more than about 10 percent alcohol will be a net diuretic effect so you'll lose water in the long term rather than replace it. So if you are going to have a nice loss of Shiraz of an evening, make sure there's a glass of water to go with afterwards to put the water back.

Eusebius - Reggie in Bedford View. Good morning to you.

Reggie - Eusebius, good morning. Chris, good morning to you.

Chris - Hi Reggie.

Reggie - It's ironic, the question that was posed by the caller before me regarding coffee, because my specific question is related to a spirit, which is whisky. I've been drinking whisky for plus forty years Chris, and I've always been diluting my whisky with either Appletise or you know the ginger that my friends always used to laugh at me and say you wasting the scotch. But recently a friend of mine directed me to dry lemon because it's mixed with quinine or aquinnine, whatever the name is called. I just wanted to know from you if you can maybe relate to differences and the benefits of how really to drink a real real scotch?

Eusebius - I didn't see that one coming!

Chris - It's a bit early in the morning, but I don't mind saying that it was a really nice Scotch. Actually if you asked the oficianados, the people who really know what they're talking about - and I'm not one of them - they do actually use water. And you're not supposed to drink the spirit as neat firewater, you are supposed to add some water to it because actually it takes the edge off and you can really enjoy it. You won't be losing anything by not adding water in terms of the alcoholic content because everything that you swallow will have the opportunity to be absorbed and you'll still get just as drunk. But actually the water that you put with it does it does tend to smooth the flavour a bit. so if you have a decent fine whisky, a small amount of water to go with, maybe 50/50 that's what I've been doing, and it does taste extremely nice. And maybe maybe a real whisky expert can tell us why water's the best choice of mixer. It certainly is for me. But you know whisky is the spirit, it's got lots of alcohol, it taste good. You can put it with with a range of things and, you know, I talk to people who mix it with everything. so I don't think you're completely unusual by mixing it with Appletise, although that's a relatively new one on me.

Eusebius - Thanks Reggie. David, good morning to you. Welcome to the show. David has lost his voice and maybe he's gone to find some scotch. Sven, good morning.

Sven - Morning, how are you guys doing?

Eusebius - We're well thank you. What's your question?

Sven - I've got a very odd question for the scientist. I'd like to find out if it is possible to harvest the electricity that comes from the lightning, and if it is possible to harvest that telectricity have we ever thought of using [**] for the spikes to try and harvest that power that are in spikes.

Chris - Did you say Sven or Shwen?

Sven - Sven.

Chris - Ah Sven. Lots of people have thought about trying this because lightning is electricity. Benjamin Franklin, the famous American electrician was the first to prove that actually whats coming down from the sky is electrical energy. When he did an experiment - very dangerous you should never do this - he flew a kite into a thunderstorm and was able to tap a stream of sparks off of the kite string via a key onto a metal rod driven into the ground, thus proving that this seemed to be the same stuff that you could generate with static electricity by wrapping things together say some amber and a pair of tights or stockings, which is what other people were doing at the time to make electricity. And also the electricity that came from batteries that people had invented by then. So people thought well, there's all this electricity up in the sky, so is it possible for us to tap that electricity down and collected it in some way...

First of all you have to do some maths. How much electricity is there in a lightning bolt? Well lightning, probably its millions of volts and its probably about 1 to 12 billion joules of energy in every lightning bolt. You think well, you know, 10 billion joules that sounds like a lot but, actually, if you work it out that would make you about 100,000 pieces of toast or it would run a 100 watt light bulb for about 100 days. And you think how many people live in a city. Not very not very many people would have their lights on for very long with the energy in a lightning bolt. Then you've got the whole question of well how do we get the energy out of the lightning? You'd have to have some way of collecting lightning. So you'd have to have a lightning conducting system that could lure lightning to one place, withstand the blast, and then store the energy in some sensible way, and then redistribute the energy in some sensible way. And when you take all the costs of all the infrastructure into account the return just doesn't justify the end, so we don't think that this is a very viable way of doing it.

Eusebius - Jim, welcome to the show. What is your question?

Jim - Hi. Let's just assume that I'm standing still and there's an object to my right that's travelling at three quarters the speed of light towards me. And to my left identical at three quarters the speed of light, which means that they are closing on each other at one and half times the speed of light. Wouldn't that break the rule of the maximum speed only being the speed of light?

Chris - Hello. Good question Jim, but the answer is no. Because relative to you, those things are approaching you at a combined speed that's maybe faster than the speed of light if you counted down the time, but the individual things that are moving are not breaking the barrier of the speed of light. The speed limit for things moving is the speed of light. And the reason for this is that as you accelerate things you have to give them energy to go faster. If something goes faster, and therefore has more energy, because E (energy) equals MC squared where M is mass. If you increase the energy of something because C squared the speed of light doesn't change, the mass must increase. So as things go faster they get heavier, snd if things get heavier they need more energy to accelerate them. So, therefore, eventually you get to a point we need an infinite amount of energy to make something go faster so, therefore, it can't grow faster than the speed of light. But because the objects in your experiment are not themselves individually breaking the light speed barrier, everyone's happy.

Eusebius - Jeremy good morning. Welcome to the show.

Jeremy - Hi Eusebius. And Chris, good morning. My question is can something become nothing. For example, a grain of sand as it erodes what happens to the component parts? Do they just disappear from the face of the Earth? Similarly the ashes of a burnt tree, what actually happens there?

Chris - Hello Jeremy. The answer is that everything that you see around you is made up of atoms. This is one reason why you should never believe what an atom says because they make up everything - bum bum. But the point is that atoms can't be destroyed unless they radioactively decay and turn into a new kind of atom, an atom is an atom.

It's an element, and those elements combined together to make compounds, and sand is made of silica, the ash that is in a tree is also bits of silica. There'll be carbon things there and various other compounds. But as you break those things down and make them smaller and smaller they don't disappear, they just turn into smaller particles that eventually are too small for you to see, so nothing disappears. You can't make these atoms evaporate and they'll always be there, they'll just be too small for you to see.

Eusebius -Okay, thanks for that question. Kurt, good morning to you.

库尔特,我想知道如果你to run a cable from the bottom of the Earth through into space and you use the vacuum of space as sort of the pulling of space as a way to generate energy?

Chris - There are problems with doing this. There's a material science problem because you've got to get your tether up into space. A cable which is going to be 100 miles or 200 miles long to get it out somewhere into space. And then if you want it to where the International Space Station is that's - I'm mixing all my units up here, but that's about 400 kilometres up, so it's a really long way out there. So I'm not really sure why it would be useful because you've got enormous windage effects, because you've got the airstreams at different layers of the atmosphere putting a force on this stuff, and its going to be a really big material science problem. We haven't got materials that are capable of doing this very well at the moment. And why would we want to do it? I'm not sure what we would achieve. Theoretically you could send a cable out into space but what would be the benefit?

Jeremy - Do we not run cables from that are sort of in the ocean that are more than 400 kilometres long already?

Chris - Yeah, but they're not subject to the effects I'm describing. They're reinforced cables that sit along the underside of the ocean. If you want to send a cable up into the high atmosphere you've got to support the weight of it. Its got to be strong enough to support its own the load on it, because the cables that are conveying information under the ocean are not under load. If you're going to put something on a tether out into space, its going to have an enormous amount of load on it from winds hitting it, from the object on the end of it, etc. So you've got to engineer the ability to support itself as well as whatever's on the end of it and all of the other effects of the atmosphere and so on. So I'm not really sure - what did you have in mind putting on the end of your cable?

Jeremy - The idea is because the idea come from a space elevator that people sometimes talk about. But if you had a cable car running into space, and used the vacuum of space, I feel that you could generate energy from it because you're using the pull of space, the vacuum itself, and the cables connected to a turbine down on Earth, or wherever on Earth and it generates its own energy, and its energy without any use for.

Chris - Well that sounds like a perpetual motion machine and, unfortunately, that's not going to work. Because, if you think about it, for something - I see where you're going with this because if you've got a vacuum in space and you've got lots of air pressure on the surface of Earth why can't we run a turbine up the inside of your tube or whatever and the air flowing into that vacuum would drive a turbine and we get some electricity. The problem is that the air has got to be lifted away from the Earth's surface so it's doing work against gravity all the way up. And the thing that's forcing the air up the tube is the weight of air above the air. But as the air rises up the tube, then there's going to be less weight of air to propel it further, so eventually it's going to, like a spirit level, even out and there's no net force to keep pushing out into space. Gravity will it win win in the same way as it holds the atmosphere against the Earth's surface, so it wouldn't actually work unfortunately.

Eusebius - David, good morning to you.

大卫,你好,克丽丝。我想知道你这什么nk of my theory about weight loss. If I do some exercise before I go to bed thereby depleting my blood sugar. I then go to bed and for eight hours now the body has got time to draw on its flux loss in order to replace the blood sugar level. Is this idea any good at all?

Chris - Hi David. I think the idea is brilliant in the sense that doing some exercise is better than doing no exercise. But I think that it'ss slightly flawed in terms of when the best time to exercise is because that's going to be different for everybody. Because some people are going to find that they are more motivated at certain times of the day. Some people also find that their appetite changes across the day, their ability to actually do exercise meaningfully changes across the day. So I think the bottom line is exercise is definitely the way to go because it boosts lean tissue and it burns calories, so you're increasing your potential to burn calories and you're also directly influencing your burning of calories. The other thing to bear in mind with any kind of weight loss strategy is that energy in must equal energy out or, as they put it in Australia, Calico - calories in, calories out. You've got to keep that in balance otherwise there'll be a change in weight either up or down depending upon which way there's an imbalance. So exercise is good, exercise is good on a range of different levels, not just because it burns calories but because it makes you healthier anyway. It's good for blood pressure, it's good for muscle strength, it's good for actually preventing diabetes and obesity. But I would do exercise when it works best for that person and try to change your eating habits during the day so you eat most of your calories earlier in the day and fewer calories as the day goes on. The old adage is you should have breakfast like a king, lunch like a prince, and dinner like a pauper. The idea being that you're not having a massive great meal in the evening when your body doesn't really have anything to do with all those calories.

Eusebius - Dale, good morning to you. You've got questions about what the science of solar energy?

Dale - Yes, good morning. I want to ask the scientists. Look south Africa is [**] sunlight. Why can't we harness the sunlight in terms of our buildings that we have? Instead of having normal window panes having some type of solar panel installed in the buildings generating electricity?

Chris - Yep, I think you should go and get a job in government if you haven't already, because that's exactly what the country needs to do. And it's ironic that many of the countries with the best sun record, as in more days of sunshine, have some of the poorest installations of solar panels. I mean I used to go around Australia and be gobsmacked by the paucity of solar panels I would see in Australia, given that this is one of the sunniest places on Earth. South Africa, another very sunny place. Australia is beginning to sort it's solar situation out. I think South Africa has enormous opportunities here and, of course, what you can do with solar is to drive desal. And you can use the very energy intensive process of desal you can drive that with solar energy which means it's then not contributing a huge carbon contribution to the atmosphere. And it's not costing you a fortune but it is returning a very valuable thing which is water. And then your point about buildings. Isn't it strange that we create greenhouses for ourselves to cocoon ourselves in. We then get too hot because the sun comes streaming in through these windows of these posh buildings covered in glass, which is de rigueur these days and then we have to spend even more money throwing the heat away that we've collected. Why not do what you're suggesting and come up with better devices which actually turn those windows into solar panels. Companies are doing this. These devices do exist and they have ways of actually turning the roofs of buildings, the walls of buildings, and the glass of buildings into sunlight collectors to then do a range of things. One is directly generating electricity. In other cases to do things like electrolise water to produce hydrogen, which you can then feed into a fuel cell and use that energy usefully. So people are doing this but it just takes people to implement it.

Eusebius - Stunning. Chris, thank you so much. Every week we love learning from you and we'll do it again next week. Have a beautiful weekend.

Chris - Already looking forward to it. Thanks everyone. Have a great weekend. See you next time!