 Canals is still going round and causing your cupular to deflect. Anybody can do that. We can do another type of dizziness because there is, in fact, three types of dizziness. Normal dizziness is rotation in the horizontal plane, that's rotation of the fluid in this semicircular canal, but we can get rotation in another semicircular canal just by doing a slightly different type of rotation. So now, all I need you to do is I'm going to spin you around ten times. You need to close your eyes, not yet, but rather than just looking there like that, I want you to put your chin on your chest and look down at the ground. Close your eyes, chin on your chest, look pointing towards the ground. Can you do that? Okay then. So now when we do this though, folks, it's very important that we remain quiet because your brain takes orientation cues from any source. So if it can hear you talking, it says, oh yeah, well there's people over there, I kind of know where I am. So the quieter we are, the better the effect. So you're going to have to lift your legs a little. You ready? So ten times round and when I'm finished, I just want you to open your eyes and raise your head back up normally. So there we go, we'll bring you to a halt now. So just open your eyes, now, see the way he's leaning over in this direction. Now I want you to remain standing now, remain sitting now. What's happened is we've caused rotation in this ring by putting that in the horizontal position now. So he feels like he's going in that direction. I strongly advise you all to try this at home. No I do, but one important safety feature. You must do it on a chair that has armrests because the sensation that you're moving is so strong that when you open your eyes, you think, oh I'm going in that direction, you throw yourself off the chair. Now I'm going to wheel you over to the steps and then we're going to help you down into your seat. Will you be able to get down those steps yourself now? Right. An even worse type of dizziness, if we wanted to do rotation in this semicircular canal, what you do is you put your head down and then you look towards the direction that you're going to spin and if you do your ten times rotation there, open your eyes, just bring your head back up, you feel like you're doing somersaults, backward somersaults and if you do that, you must be on a seat that has a back on it. So I do strongly encourage you all to do it, but do it in a seat with two arms and the back. All right? And that sense of disorientation, Andrew, you may find you feel a little nauseous for about maybe five minutes afterwards. It's like the worst case of motion sickness you've ever had, but if you like roller coasters then there's no problem. So we'll move swiftly on to the physics of liquids. There should be a lot of fluid dynamics going on in the body because you're a big bag of fluid. So if you're thinking about fluid dynamics, the most important effect in fluids as far as medical physics is concerned is the Bernoulli effect. Anybody ever heard of the Bernoulli effect? You probably don't do it in a leave and serve, but it's a very interesting thing. I can show you it here. Where's my mouse? See, wherever you have a moving gas, that's at a very low pressure. If you've got a stationary gas, it's at a high pressure. It's kind of counter-intuitive, but you can see here the ball is trapped in a column of moving air. The air all around it is stationary, so at a higher pressure. So you've got a Bernoulli trap that's called. You can show you another example. 1982 World Cup Brazil versus France, free kick, oh, the fool has missed, but hold on. The curve on the ball is created by the spin. The person kicks the ball to one side, that creates a spin, and you get different velocities of gas side to side. You get a lovely spinny effect, and it gives you a sideways force. More importantly in the human body, we have the aneurysm. Anybody ever heard of an aneurysm? It's an abnormal swelling in the body of a blood vessel. Now it could be due to prior trauma, it could be due to old age or genetic predisposition. You know the way if you're in the back garden watering the plants or washing a car, if you stick your thumb over the end of the hose pipe, what happens to the water? Does it speed up or slow down? If you stick your thumb over half of it, it speeds up. So if you reduce the cross-sectional area, you increase the fluid velocity. Here we've done the opposite. We've increased the cross-sectional area. So when the blood comes in, it slows down. Bernoulli says, well, if it's a lower velocity, that must be a higher pressure. A higher pressure means we'll just make this aneurysm a little bigger. So now it slows down even more and the pressure gets even bigger and the aneurysm gets even bigger and it grows and it grows and it grows until eventually, pop, goes the aneurysm. You get what's called a resecting aneurysm. If this is the aorta, from the moment the tear starts, you've expanded the blood vessel beyond its elastic limit. So from the moment it starts to leak blood to the moment that they put the white sheet over your head and wheel you down to the morgue, you're probably talking about maybe two to three hours. So unless you get an aneurysm surgically treated, there's a very poor outcome involved. Now what they usually do is they'll diagnose an aneurysm and they'll say, oh, you've got an aneurysm, we're going to operate but not now. Come back in two months and we'll measure your aneurysm and it will have grown a little bit because this growth process takes place over months. So they'll measure it in two months time, oh, it's a little bit bigger, don't worry. Come back in two months and they keep monitoring it until eventually they say, oh, a bit big, I think we'll operate. And then they'll cut there and there and then just stick the two sides together and that's your aneurysm. So it's a fantastic example of the Bernoulli effect, but there's an even better one in the body, the fars. And we're all going to have a go at this, we're going to make an origami anus. The ancient Japanese art of paper folding will make a paper anus for us all. Take your sheet of paper and fold it along the long axis, corner to corner, so you've made it half the size and do a nice sharp fold, you're right? And then just tear along that fold, so you've got two small sheets. Come on, it's not rocket science, you're just tearing a piece of paper in half. Hold up your two sheets of paper by the corner. What we're going to do is you're going to place one sheet either side of your mouth and you're going to blow, before you do it, predict whether the paper will flare outwards or stick together. Think in your mind what you would expect to happen and then one, two, three, have a go.