Frogs Croak in Ultrasound

US researcher Albert Feng and his colleagues have found that a species of Chinese frog that lives in a noisy environment has evolved a clever way to prevent its croaks being drowned out by the sound of nearby running water - it croaks in ultrasound. The researchers discovered the strange vocal habits of the concave-eared torrent frog, which lives in a mountainous region of China, by accident when they used sensitive recording equipment to monitor the frogs activity. As well as croaking the conventional way, these frogs were also producing very high pitched noises, inaudible to humans. When the researchers recorded the sounds and played them back to captive frogs they found that their study subjects croaked in unison with the recording. To find out how the frogs were responding to the ultrasound the researchers then temporarily blocked up their ears, instantly stopping the karaoke. Feng and his team believe that the sounds are a mating call designed to cut through the loud noises of running water which are prevalent in the frogs aquatic environment. They are now eager to track down some females to see how they respond to an ultrasonic "ribbet".

19th Mar 2006

How Venus Express Will Hit The Target

Daniel - As we speak, the European Space Agency's Venus Express is en route to its namesake destination in one of Europe's most ambitious planetary expeditions ever. Venus Express will spend 500 earth days in orbit aiming to unlock the hellish secrets of the planet's runaway greenhouse effect, atmospheric collapse and possibly still - active volcanoes. But before any orbit science can begin, Venus Express has to get there and navigating the space craft through more than 400 million kilometres of interplanetary space is one of the most difficult and mathematically challenging aspects of the voyage. It's a devilishly difficult problem as computations must take into account all sources of gravity working on the space craft. These include not only the Earth and Venus, but also the sun and other planets in our solar system. ESA scientists use good old fashioned classical physics, first clarified by Newton, Kepler and others some 400 years ago. Rudiger Cramm is a flight dynamics engineer on the Venus express team at ESA's Spacecraft Operations Centre in Darmstadt, Germany.

Rudigar - The fundamentals in classical physics is still applicable. We also have to consider effects of relativity but the main principles are all from Newton and Kepler.

Daniel - Venus Express travels to its destination following a three-part trajectory, first starting with launch, ending with escape velocity from our own planet.

Rudiger - The launcher gave us velocity high enough to escape from the Earth. The second and main part is the transfer part. The spacecraft now moves mainly under the influence of the sun for about five months until we reach Venus.

Daniel - As Venus Express approaches the planet on April 11th, it will be travelling at the incredible speed of almost five kilometres per second, with respect to Venus. This is about five times faster than a machine gun bullet. It will have to slow down by about 25% of that speed to be captured by Venus' gravity.

Rudiger - The situation there is similar to playing golf. When you play a golf ball too hard, the ball will slipover the hole. To avoid this with our spacecraft we have to perform a breaking manoeuvre and Venus can capture the spacecraft.

Daniel - The aim is to end up in a 24-hour orbit around the hothouse planet. The risk is that if any problems occur, the spacecraft could miss its window for capture, making its recovery extremely challenging. Join us again next week as we join engineers working on ESA's network of ground tracking stations to learn more on how mission control send commands to spacecraft in deep space and how data that Venus Express gathers will be returned to scientists here on Earth. For the European Space Agency, I'm Daniel Scuka.

March 2006

The Cambridge Science Festival

Chris - Here's a round up of what we got up to yesterday at the Cambridge Science Festival. One of the first people I spoke to was the person who opened the festival for us here in Cambridge, and that was Carol Vorderman. I asked her what she thought of last year's sudoku craze, which she was very much a part of.

Carol - I was addicted. Well I still am actually. I couldn't go anywhere without taking one with me and I've now managed to control my addiction. I've got it down to one or two a day but I think we should have sudoku patches being sold in the chemist, it's that bad!

Chris - What do you think makes them so addictive, Carol?

Carol - I don't know. I think they access a particular part of the brain. I've been trying to get people into number puzzles for decades now, and a lot of people glaze over when they see numbers. But sudoku seems to reach a particular part of the brain and to let all of those other thoughts escape. You can just have a sense of pure thought.

Chris - It's been a little while since you were in Cambridge studying. What did you actually do here?

Carol - I did engineering here and I was at Sidney Sussex college. I was one of the poorer students I have to say! I had a third in every year of the tripos and I believe the students now in honour of that call getting a third 'getting a Vorderman'.

Chris - But this kind of event wasn't happening when you were here. What do you think of it?

Carol - This is brilliant. It's the first time I've been and it's packed. People who've come aren't scientists and they're not at all associated with the university under normal circumstances. They're just here because they want to learn something, have a bit of a good time and see what's going on. It's brilliant.

Chris - Almost certainly minding her Ps and Qs, that was Countdown's Carol Vorderman, proving that not even a maths guru on Countdown can get a first class degree from university. Now sticking to the educational theme I then spoke to the Vice Chancellor of Cambridge University, Professor Alison Richard, about what the Cambridge Science Festival is really trying to achieve.

Alison - It's all about trying to increase the understanding of the deep incredible interest of science and its importance and how it can explain and illuminate the world. The mechanism whereby we're doing this is through really interesting experiments which are a lot of fun.

Chris - Why do you think it is so important to get the message of science out and tell people in the public domain what's going on in universities like Cambridge?

Alison - I think it's really important to capture the imaginations of children about the importance of science and the fact that they might grow up to study science and then go on to do something in science. If we have planted the seeds of that idea and that ambition into some of the children here today then that will have been a great thing to do. When you watch their faces, I've seen a lot of children this morning looking just so rapt with interest and attention.

Chris - That was Alison Richard, the Vice Chancellor of Cambridge University talking about why the Cambridge Science Festival is so important for increasing public interest in science. Now one person who's already very much interested in science was found spinning on a chair in the middle of the lawn. Anna Lacey and Dave Ansell got her involved in some kitchen science.

Fiona - I'm Fiona and I'm 13.

Anna - And where have you come from today?

Fiona - I've come from Enfield in London.

Anna - Woah so we're getting people coming from all over the country to Cambridge this very day. So Dave, can you tell us, what has Fiona got to do?

Dave - Fiona's sitting on a chair that will spin really easily. I want her to take hold of these two bags of rice, one in each hand.

Anna - How are your muscles feeling Fiona?

Fiona - They're fine!

Dave - Ok, what I want you to do is to hold your arms out straight and stick your legs out forwards. I'm going to spin you gently.

Anna - So Fiona's now spinning around with her legs out.

Dave - Now I want you to pull your arms and legs in towards your body. Now put your arms back out again and pull them in again. Ok, we'll stop you Fiona.

Anna - Now Fiona, can you tell us what happened when you stuck your arms out and then brought them in?

Fiona - When I brought them in, I started to spin faster than I was when they were out.

Anna - Dave, what was happening?

Dave - Well if you think about how far the weights have got to go when you've got your arms out, it's like a great big circle. When you pull them in, you have a much smaller circle so it's much less distance for them to travel. So even if they were going at the same speed, it would take much longer for them to go around the big circle than the small circle. Also, did you notice that it was quite hard to pull the weights in?

Fiona - Yes.

Dave - When you pull the weights in, you're fighting against a pretend force called centrifugal force which gives the weights even more energy and you spin even faster.

Anna - So it's not only because you've got less distance to travel when you pull those bags in, but you're also putting in extra energy which speeds you up even faster.

Dave - That's right Anna.

Anna - Wow, that's absolutely amazing! And have you ever done any ice skating?

Fiona - Yes but I don't think that I'd be able to spin round for very long.

Anna - Did you feel sick at all?

Fiona - Yes.

Anna - Why do you feel sick Dave when you've been turning round really quickly?

Dave - Well the way your head knows which way up it is, is that inside your head there are lots of tubes called semi-circular canals. Inside is a liquid. If you start spinning for a long time, the water starts moving round and round the tubes. When you stop, it carries on going and your brain thinks your head is moving. The reason why it makes you feel sick is that there are lots of poisons which confuse these parts of your ears and so your body thinks that maybe it's been poisoned. In case you've eaten something bad, it throws up.

Chris - All in a spin. That was 13 year old Fiona with Anna Lacey and Dave Ansell finding out about the science of giddiness and why spinning round on a chair makes you want to throw up. Now speaking of throwing up, what about the science of dragons and throwing up fire? We got talking to Henry Gee from Nature magazine about his new book, the Science of Middle Earth.

Henry - I do two things. I talk about how you can make these things happen. How do dragons breathe fire? How do the balrogs, these demons, fly? How do orcs reproduce? Tolkein never talked much about sex but that doesn't mean that I can't, so I've had a lot of fun doing that.

Chris Well I've met some people who almost do have breath as bad as breathing fire, but how do you think dragons could have fiery breath then?

Henry - Well I thought it was actually not that difficult. All you need to do is have something that fumes a bit, has a very low critical point and ignites very easily if mechanically in contact with something. So I thought, easy! Diethyl ether! I had the most incredible ether fires when I was at school. All you have to do is tip it from one test tube to another and it ignites. So if you have a dragon making ether in its ether glands, all it would do is breathe it out across its teeth and you'd get a flame. As everyone who's had laboratory accidents know, a little ether goes a long way.

Chris - Well it is the Naked Scientists, so let's get back to the sex. Orcs and sex: tell us about that.

Henry - Well Tolkein said that there were boy orcs and girl orcs but then he lost the plot after that because no - one knows how orcs were made. I think that lots of orcs were parthenogenetic, in other words they're all girls and reproduce without sex at all. You think that they might look pretty male, but then so do female hyenas. They're so doped up with testosterone to go and do battle with other female hyenas. We don't actually know this with orcs because nobody actually sees an orc without its trousers on, so it has to remain in the realm of hypothesis.

Chris - Well let's hope it stays that way. Now from fiery breath and orc sex to eyeballs because I caught up with nine year old Euan at Crash, Bang, Squelch, one of the very hands-on activities at the Cambridge Science Festival and asked him what he thought about the prospect of cutting up a sheep's eyeball.

Euan - I think it's really fun and it's really exciting to be here for the second time.

Chris - So obviously it was good last year because you've come back, but what have you done so far today?

Euan - So far we've done Crash, Bang, Squelch and we've had a little look at some other things.

Chris - One of the things I've just seen you fiddling with is a sheep's eyeball. Tell us about that.

Euan - Well we learnt all sorts of things about the eyeball such as it's got black stuff inside the eye. With the black stuff there is jelly, which I never knew.

Chris - Did it help to get a real eyeball and chop it up for you to understand what goes on inside your own eyeball?

Euan - Yes it did, except a sheep gets more night vision because it's got colour in its eye.

Chris - There's a reflective layer on the back of the eyeball isn't there? I bet you don't know the name of it.

Euan - Um, no I don't.

Chris - Do you want to know the name?

Euan - Yes please.

Chris - It's called the tapetum lucidum. That's a Latin word and it means bright carpet.

Euan - Does it? I'd never have known that. Thank you.

Chris - And what would you say to anyone else listening to this thinking whether they should go to the Cambridge Science Festival?

Euan - I would say, go now!

Chris - You heard him. That was nine year old Euan doing the big sell on sheep's eyeballs. He was there at the Cambridge Science Festival's Crash, Bang, Squelch, and before that, you heard Dave Ansell our regular Kitchen Science guru doing a little bit on the science of giddiness.

March 2006

Invasive Species And Zebra Mussels

Dr David Aldridge, Department of Zoology, University of Cambridge

Chris - Tell us a little bit about the problem of invasive species, because rabbits are very much in your face in Australia but what about other more subtle examples.

David - Invasive species are one of the biggest threats to the world's ecosystems and wildlife. Many species go pretty much unnoticed until we start looking in a bit more detail. I work in rivers and lakes, and there some of the biggest threats to natural biodiversity are from non-native species getting in. A good example that we're working on at the moment is something called the zebra mussel, which has actually got into the Great Lakes of North America and is spreading through Britain and threatening our native organisms.

Chris - What does it look like?

David - It's very much like the marine mussels that you like to eat but it's a freshwater version. It as a beard or byssus thread which it uses to attach to solid surfaces, and it has a stripy shell, which is where the name zebra comes from.

Chris - How big are they?

David - They're about three centimetres in length.

Chris - So they're quite small actually compared with the big things you see on the dinner table in the South of France.

David - Yes, they're small but they live at really high densities. When they get into places they can live in densities of over 100 000 in a square metre so they engulf absolutely everything.

Chris - So where do they tend to make a bee line for?

David - They do very well in rivers and lakes and they're not very choosy. This is one of the characteristics of invasive species, that they can often live in a broad range of habitats, are generalists and can get into disturbed habitats very quickly. In the case of zebra mussels there's nothing else in freshwaters that attaches to solid surfaces, so they can exploit unexploited niches.

Chris - So why are they a problem?

David - They've got a lot of publicity, especially in North America, because they affect industry by blocking pipes in power stations. They've closed down water treatment processors and that's because they can attach to surfaces. In North America they cost five billion dollars a year. From a conservation viewpoint they're very worrying because they change the entire nature of the ecosystem them invade. They'll sit on top of anything solid including our native mussels which they choke and smother. We have a rare mussel in Britain called the depressed river mussel, which gets completely covered in zebra mussels and is completely prevented from breathing and feeding.

Chris - How did they get here?

David - The zebra mussels have a really interesting method of dispersal in that they have planktonic larvae that can remain in the water column for up to a month. A lot of the overseas dispersal has been in the ballast water of ships. Ships will go from one freshwater port to another, cross the sea and dump the water when it gets to a new port. So actually this is one of the major vectors of invasive species. There's been some work done on ships moving from Japan to North America, and they've found over 300 non-native species living in the ballast water. So now there's a big move towards treating ballast water to control all the little invasive pests inside.

Chris - I guess no-one thought about the potential for this problem when ships began to do this.

David - No, and still it's very difficult to regulate. A lot of people turn a blind eye and don't actually recognise the value and importance of it because changing ballast water out at sea is costly and time consuming. People don't want to do it.

Chris - You made headlines fairly recently with a novel approach for dealing with this problem.

David - Yes. I'm a conservation biologist but on this occasion I've actually been out to kill the pests so that's a slight challenge to my nerve! We've developed something called the Biobullet, which is an environmentally friendly solution for controlling zebra mussels. This is particularly something that you can use in pipelines and in industry. Traditionally, if you pour bleach down a pipe line, which is what they do, the zebra mussels are very clever, sense the toxin and close up their shells. What we've done is encapsulated the toxins, in this case a salt, in a little edible coating which tricks the zebra mussels into eating it. They think they're getting tasty feast and they concentrate it out of the water as they busily filter out the food. They then swallow this toxic pill without realising it.

Chris - And why doesn't this take down native wildlife?

David - What we do is put it down a pipe line and engineer the coating to break down within two or three hours of going in the water. So all the water that goes out into the wider environment has pills that have already degraded and the salt has dissolved so there's no toxic build up in the environment.

Chris - Why isn't this a problem in parts of the world where these mussels are native?

David - That's a very good questions and very often when people are trying to find ways of controlling invasive pests, they'll go to their native range and ask why is it that these things are being kept under control. Sometimes it can be a biological agent such as a predator or a virus or a parasite which has evolved in association with that organism and keeps it in check. But often when species are taken out of their range, there's nothing present to regulate it and this is why invasive species often do very well in island habitats where there is a low diversity of organisms. There's a lower chance that there's going to be something there to actually eat it or kill it through disease.

Chris - What's the chance of something evolving to be able to prey on it and therefore make the problem go away?

David - There are possibilities over time. Often invasive species will establish, become very abundant and then the ecosystem will adapt in that those organisms that can deal with the invasive species are selected for and therefore start to persist. But in the meantime, we've got problems with these invasives just establishing and causing us ecological and economic problems.

March 2006

The Tide of Toads Plaguing Australia

Professor Rick Shine, University of Sydney

Chris - Now another invasive species is the cane toad. They were introduced to Australia in 1935 from South America and the idea was to try and control insect pests that were laying waste to Queensland's cane fields. Unfortunately, the result has been a massive disaster. Bufo marinus, which is the Latin name for a cane toad, can live for fifteen years and it produces 30 000 offspring per toad every single year. As well as being highly invasive, it's also extremely toxic. This is having a devastating effect on Australian native species that are particularly partial to a toad-sized meal. Sydney University's Rick Shine has been watching the advance of the tide of toads as they move west across Australia.

Rick - In studies at the invasion front of this feral toad that's roaming across Australia, we discovered that they're moving much faster now than they were when the invasion started. Looking at the movement patterns of toads up in the bush near Darwin, we've found that longer legs help toads to move faster. Sure enough, the toads at the invasion front have got substantially larger legs than the ones further behind.

Chris - And it's taken 50 or 60 years for them to develop this trait?

Rick - The toads were introduced to Australia about 70 years ago on the other side of the continent from where we're working on them, so they've covered about a million square kilometres over 70 years. From our work, it looks as though they're getting faster and faster.

Chris - So how fast does a toad hop in the average day?

Rick - If you look at the toad, it really doesn't look as though it's made for speed. When we first started, I'd expected that a toad would be pretty tired after moving 50 metres in a night. But when we strapped little radio transmitters onto these guys at the invasion front, we found that they were moving often half a kilometre or a kilometre in a single night. They keep moving in the same direction. Basically, they seem to have a compass in their pocket and they're just heading west.

Chris - That's an extraordinary distance for something which is five or six inches long to have covered in a night.

Rick - I'm astonished at how far the toads can move. These first toads that arrive at the invasion front are really incredible active animals. They spend the day hidden in grass, but as soon as the night falls, they go straight back to the main road, face west and start hopping.

Chris - Now you mentioned the invasion front. What have you actually done to watch these guys as they make their progress west?

Rick - Well myself and my colleagues have been mostly studying the snakes at an area not too far from Darwin for about 20 years. We've got a study site that we actually understand pretty well. The toads have just arrived. As a toad arrives at our study site, we're out there every night looking around catching the toads, we strap a small radio transmitter with a little waist band around to hold it on and let the toad go again. We then locate the toad every day. That way we build up a picture of where they travel, how far they travel and what direction they're going in.

Chris - And what about the study on the leg length? How have you made that finding?

Rick - Well we were interested in the fact that toads seem to run along the road rather than in the bush. The obvious reason was that you can move much faster on the road. So we ran some very simple trials over short distances and we discovered that toads are quicker in the open ground but also a toad with longer legs is quicker than a toad with the same body length but shorter legs. We thought that in an invasion, the animals at the front will be the fastest ones. There will be continuous selection for the fastest animal. Now if that's the case, what you should find is that the toads at the front should be faster than the toads further back, and from our little series of race way trials, we thought it might turn out that the toads at the front might have longer legs than the guys at the back. Rather to our astonishment, that's exactly the pattern that we found.

Chris - Are there any disadvantages that go with longer legs?

Rick - It's really intriguing that leg length decreases consistently with how long toads have been in an area. If we look at the samples that have been taken and put in museums over a 60 year period in Queensland, it's clear that relative leg length is decreasing year by year. Now that really does suggest that there's some cost to having long legs but we have no idea at the moment what that cost might be and we're' very interested in what that might be. We're trying to run a series of trials to test ideas.

March 2006

The Plight of Lonesome George

Dr Henry Nicholls, science writer and author based in London

Chris - Tell us about the story of Lonesome George.

Henry - George was discovered in 1971 on a very remote island in the Galapagos. Charles Darwin passed through in 1835. This island was thought to have lost all its giant tortoises.

Chris - Where did they go?

Henry - During the 18th and 19th centuries, sailors and buccaneers came through and basically ate them.

Chris - Why were they particularly good as a food source for sailors?

Henry - It's really because they don't need food or water to stay alive. The sailors would collect these tortoises, take them on board, flip them upside down in the hold and they would live for as long as a year on board and survive. When they were killed a year later, the sailors could have fresh meat.

Chris - Do they taste good then?

Henry - Allegedly they do. I can't say I've tried or would try them. Darwin noted in his writing that the young ones in particular made excellent soup.

Chris - So how did Lonesome George end up being the last one?

Henry - This island he live don got particularly hard hit and the last ones were collected in 1906 and nobody saw any more until 1971 when they found this single male. He was taken into captivity on a different island and he's been there ever since.

Chris - What are the prospects for him?

Henry - They're bleak, frankly, as far as his reproduction is concerned. As far as his status as a conservation icon is concerned then they have never been better. George is really an awesome ambassador for the conservation cause in Galapagos and even beyond.

Chris - He's thought to be 60 to 100 years old isn't he?

Henry - We can say he's definitely 60, and tortoises might love as long as 200, although nobody really knows. They're thought to be the longest living animal on the planet.

Chris - In terms of rescuing him, genetically speaking, is it possible to cross mate him with another related tortoise so you might be able to rescue some of his genes?

Henry - There were originally thought to be about 15 different types of tortoise of the different islands, which they call subspecies. That indicates that they're not entirely different species and are sufficiently closely related that they can breed with each other. Two females from a different island have been in George's enclosure with him since 1992, but he's shown absolutely no interest in them. He's quite adamant that he's not going to mate with them.

Chris - But he has had a girlfriend hasn't he?

Henry - He has had a girlfriend, and this is the lovely story that got me interested in George in the first place. Very shortly after these tortoises were put into his enclosure, a Swiss zoology graduate passed through the island and volunteered her services at the research station. She got given the choice that she could either work on geckos or she could try and collect a sperm sample for George so that they could try some sort of artificial insemination. She chose George. She spent four months trying to build up an intimate relationship with George and earned herself this nickname: Lonesome George's girlfriend.

Chris - He's also had some death threats.

Henry - He has and particularly in 1995. He became embroiled in a conflict between conservationists and fisherman that rumbled on throughout the 1990s. The fisherman wanted to fish more, in particular a species called a sea cucumber. They're a very lucrative species that's sold to South East Asia and has aphrodisiac qualities. People wanted to fish it. But the conservationists could see that this was an unsustainable fishery and tried to impose a quota. The fisherman weren't happy with it and held a machete to George's head. The conservationists backed down and let them fish.

Chris - Had the sea cucumber succumbed?

Henry - The sea cucumber is ecologically extinct. It's now overfished to the point where the sea cucumbers can't even find each other to mate, so it's another sad story. Conservationists might be able to bring individuals back together and resurrect that population but while fisherman are intent on making money, it's still a problem there.

Chris - Tell us about the book you've written about this in case people want to buy it. Incidentally, we can offer you one copy of this book which Henry will sign.

Henry - It's called Lonesome George, it come out on the 3rd April and it uses George to explore conservation much more generally.

March 2006

Conserving The Oceans

Dr Helen Scales, science writer and conservationist based in Cambridge

Chris - Now Helen, you're a marine biologist. What are the key problems if we look at the sea at the moment?

Helen - I guess the most obvious and pervasive problem in the ocean is that we're taking too much out of them. We're catching far too many fish and too broad a range of species and it's becoming more and more of a problem.

Chris - Why should that be such an issue? Why don't we just, say, catch a certain species and let the others recover? Or is that impossible to police?

Helen - Well I think the problem is that there are so many fisherman out there. Henry's already been talking about one island in the middle of the Pacific and one species that the fisherman were after. I'm sure that now the sea cucumbers in the Galapagos are declining, they are finding something else to catch. They might be trying to catch sharks and take their fins off, which also supplies a high value trade. That's one issue with the sea that the things we can catch are worth a lot of money. Fishermen can make a lot of money from shark fins for shark fin soup. Sea horse are also fished a lot for Chinese Traditional Medicines. The oceans for some people are just a very large source of money, a treasure trove if you like, and something to be exploited. The other problem with the oceans is that we feed ourselves from them. The statistics are something like half the world's population lives within 60 kilometres of the coastline and essentially rely on fish for their main protein source.

Chris - What could we do at the moment to rescue cod because that's pretty much facing instant jeopardy.

Helen - Cod are in a terrible state depending on exactly where you look and which populations. A cod fishery collapsed off of Canada in the 1980s and hasn't reopened simply because there aren't enough fish left. So yes, cod is in trouble and lots of other species are too. But we do have one thing that might be able to help us, and that's marine protected areas, marine parks, marine reserves or whatever you like to call them. We do know now that it's fairly obviously that if we leave a bit of the ocean and don't fish it, that lets the fish recover. It gives them the chance to reproduce. Not only can we find that marine parks help in terms of biodiversity and preserving species, but they can also feed the fisheries that we're relying on for luxury species and to just feed ourselves. So it's a kind of win - win situation really.

Chris - And very briefly Helen, there's an example of how NASA are helping to save fish because of the no - go zone that's been created around the Kennedy Space Centre.

Helen - That's right. The way we know it's working is that Americans are quite into their sport fishing, especially around Florida. What they've found is that the record breaking enormous fish have gone up and up since they stopped fishing around the Kennedy Space Centre, so it works.

Chris - So that's why we should be establishing more marine reserves to preserve fish stocks and big fish which are more fertile, have more babies and healthier babies.

March 2006

Hurricanes in a Lemonade Bottle

Build a minature hurricane in a lemonade bottle and find out why it happens.

What you need

A lemonade bottle

Some water

A sink

What to Do

1- Fill the lemonade bottle with water.

2- Turn it upside down empty the bottle - what happens?

3- Fill the bottle again

4- Empty the bottle again, this time swirling it - what happens?

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What may Happen

You should find that if you just empty the bottle it empties quite slowly but if you swirl it, the water creates a whirlpool and empties much quicker.

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What is going on?

For the water to get out of the lemonade bottle something has to take its place, and the most convenient thing to do so is air. So the air is trying to move up whilst the water moves down. There is obviously a conflict here, ther normal way is for some water to fall out then a bubble moves up through the neck, allowing more water to fall out. The water comes out in big lumps, which is actually quite a slow process, because it has to keep speeding up and slowing down.

However if you give the water a bit of a swirl as you empty it, something entirely different happens. Although the water is only spinning quite slowly to begin with, as it moves inwards towards the neck it speeds up to the point where it is thrown out to the sides of the bottle by centrifugal force^* so strongly it forms a hollow tube with an airspace in the centre. This allows the air to get into the bottle much more quickly than as bubbles because it is a continuous process, so even though the water is flowing out through less of the neck it will flow faster, and the bottle will empty more quickly.

Why does the the water spin faster in the neck?

There are two effects which contribute to this. Even if the water was going at the same speed at the neck of the bottle as the outside, because the circle it has to travel in is much smaller it would take far less time for it to do a rotation, so it would be spinning faster.

Also when the water moves into the centre it has to fight against centrifugal force this uses energy, and this actually goes into spinning the water even faster.

What has this got to do with hurricanes?

A hurricane starts to form over some particularly warm water, this heats up the air making it lighter and the water evaporates producing water vapour which is also lighter than air. This warm wet air begins to rise sucking cooler air in at the sides. Because the world is spinning the air being sucked in is spinning slowly to start with, as it is pulled in it gets faster and faster (just like the water in your bottle). If the hurricane is large enough this can produce winds of up to 225kph (140mph), quite capapble of hurling trees, cars and houses all over the place.

^* Centrifugal force is a pseudo (pretend) force that can be useful in thinking about rotating objects - it is the force that is applied to something else (a string, the ground etc) that is needed to keep an object (which would naturally go in a straight line) travelling in a circle. Although it is not real it is often a useful way of thinking about things.

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