University Place Wonders of Physics  2010 Physics of Sports  UP 481  cc  >> Professor Sprott has asked me to round up a bunch of physicists this year who are really good at sports. So let's get him out of here and see what he's got in mind. Ladies and gentleman, introducing our gravitational golfer, the ballistic biker, and that relativistic runner, Professor-fessor-fessor... (imitating echo) Clint-clint-clint... Sprott-sprott-sprott... (applause) § §  >> Welcome to the "Wonders of Physics." Like many of you, I've been watching the Winter Olympics. And it occurred to me, there's a lot of physics in sports. So, I thought with my superior knowledge of physics, I should be able to enter the Olympics and win a bunch of gold medals. >> Ah, so this sign shouldn't say "The Physics of Sprotts," it should say "The Physics of Sports." >> Hmm. >> And you know, you're not a very athletic person. 

I remember one time, you and I were out in the back country, and you had this really nice yellow jersey on. You tried to take a motorcycle ride, and it didn't work out. >> Well, you're right. I have had some problems in the past. (light laughter) But you know, that's why I thought we could have you bring some physicists in who are very good at different sports, and explain to us the physics that's involved in those sports, so I could decide what would be a good sport for me. Who were you able to find? >> I found some really great athletes for you, today. Let me first introduce you to George "The Judo" Junkie. § § (applause)  >> Well, Peter, I'm not going to actually be doing any judo today. >> No judo today? Why not? >> Well, I wasn't able to find any volunteers to let me throw them around. >> Well, what are you going to be able to show us today? >> Professor Sprott was right, there's a lot of physics in sports. 

And particularly in martial arts, which is about forces and momentum, and stuff. So I thought since this is about physics, I'd break something. >> Great. >> Anybody want to see me break some boards? (applause) Now, because we are talking about the physics of it, though, before I break it, I have to explain what's going on. I know, I know, but just bear with me. The first concept that's really important to understand is pressure. And pressure is force applied over an area. We're all familiar with the idea of atmospheric pressure. We hear that all the time from the weatherman, when he says what the barometer is reading. You see these two hemispheres here. 

This is a demonstration that was first, as far as we can tell, presented by Otto Von Guericke, who was the mayor of Magdeburg. That's why they're called Magdeburg spheres. As you can see, I can easily separate these, because the pressure on the inside is the same as the pressure on the outside. That pressure is approximately 15 pounds per square inch. It's a lot of pressure. When I take the air out of here, which I'm going to do now, you'll see what happens. You can see the needle is dropping down. It'll never actually reach zero, because you can't pump all of the air out, but we can get close enough. And that's close enough. Now, I'm going to ask for a volunteer. 

I'd prefer it to be a big, bulky adult, preferably. So kids, if you want to nominate an adult, go ahead and point. You sir, right there in the front row. (laughter) I'm going to attach this handle.  Your name, sir? >> Jay. >> Jay, thank you for cooperating. >> No problem. >> I'd like you to grab that end. I want to know, how many people think we're going to be able to pull these apart, like there was nothing there? Raise your hand if you think so. Raise your hand if you don't think we're going to be able to pull these apart with a team of horses. 

Raise your hand if you think we're going to pull on this and fall down. (laughter) Okay, well, in physics, we actually do the experiment. We don't just decide by vote. So, if you'd be kind enough to pull on that. Go ahead. We're pulling on this pretty good, and it's not opening. What do you think is going to happen when I open this valve? (laughter) There you go. (musical flourish) Thank you very much. (applause) (musical flourish) Now, what's the big deal about pressure? What does that have to do with breaking things? Well, as it turns out, when you apply pressure to something, it bends. And when you break something, you bend something so far that it can't return to its original shape. 

This demonstration here is a device that also has to do with Otto von Guericke. This is similar to the device that he used to evacuate the air from those spheres. It uses a principal that was first developed by Blaise Pascal, a very famous mathematician and physicist. When I push on this crank, it applies a force to this cylinder, which applies the pressure on the oil in here to this larger cylinder, and lifts the larger cylinder. You'll notice, there's a triangular head here. That will push up into this board and break it by applying a pressure on this very narrow area. That will deform the wood so it can't come back. >> This is how they lift your car in the garage, isn't it? >> Yes, exactly like this. Although, we hope they don't do this to your car.  And there you have it. 

(musical flourish) (applause) Now, something similar to this is going to happen when my trusty assistant comes out with the boards.  You can see he's a grad student. (laughter) I'm going to hit this right here, and that's going to bend the board so far that it can't recover its original shape, and it'll break it. (applause) Would you like to see that again? Okay, I'll hit it here this time. (musical flourish) (applause) I was afraid that was going to happen one of these times. >> Yowch, I don't think that's a sport for me. That looks like it would be really hard on your hands. >> Well, it can be, if you haven't conditioned your hand. And if you don't have a lot of experience, it can be very dangerous, so don't try this at home. Anyway, I want to thank you all for being such a great audience, and Professor Sprott for having me out here. 

(applause) (musical flourish) (applause) >> While he was talking, it did occur to me that there's a lot of sports that depend on having a fast reaction time. I have a demonstration of that if someone would like to earn a dollar. Whoa! Lots of volunteers. Okay, come on down.  Come down, face the audience, and tell us your name. >> Samuel. >> Samuel, okay. So, you want to earn a dollar, right? Face the audience. They want to see your face. Okay. 

Step back here, right beside me. All you have to do is put your fingers about so far apart, right in front of your body, just opposite George Washington's picture on the dollar bill. Do you know George? Who is he? >> He's the first president. >> The first president. Very good. Nope, don't grip it yet! (laughter) All I'm going to do is drop it, and you have to catch it, right? Can you do that? Oh! Can you pick that up for me? (musical flourish) I'll tell you what, you can keep the dollar bill. (applause) I was pretty sure he couldn't do that, because it's 7cm from George Washington's picture to the end of the dollar bill, and something takes about a tenth of a second to fall 7cm. Most people's reaction time is about two-tenths of a second. So, very few people can do that. It does raise an interesting possibility, an experiment you can all go home and do. 

If you don't want to give away dollar bills, take a meter stick or a yard stick, hold it like that. You have your friends hold their fingers opposite to the 50cm mark, drop it, and see how far it falls before they catch it. Of course, the farther it falls, the slower is their reaction time. That way, you could do experiments. For example, you could try to figure out whether young people or old people have a faster reaction time. Offhand, I don't know the answer, but you could do the experiment. Here's another thing I thought of just a few days ago. When you react, your eye has to see something happen. That has to send a signal to your brain. That then sends a signal all the way down your arm to your muscles, to tell your muscles to move. 

So, shouldn't someone with a short arm have a faster reaction time than someone with a long arm? I have no idea whether that's true or not, but you could all do the experiment and find out. But I know I have only an average reaction time, so maybe I better stay away from sports where you have to be really quick. There are other sports that don't involve a fast reaction time. How about something like bowling? Wouldn't that be good? >> Sure, bowling. We have a bowling ball over here. I see that. Is there anyone in the audience that is very good at bowling? Okay. How about you? Come down here. Face the audience. What's your name? >> Jacob. 

>> Jacob, okay. So you bowl, right? >> Once and a while. >> Once and a while. Yeah, about like me. Are you good at it? >> Kind of. >> Pretty good, okay. Well, that's perfect. Jacob, will you turn right, and walk over to Mr. Weix. We're going to make what we call a bowling ball pendulum. A bowling ball weighs 16 pounds. 

You put it on the end of a long wire suspended from the ceiling, and make what we call a pendulum. Jacob, what we'd like you to do is to hold that right by your nose. Good and tight. Keep your head against the wall. And when I say, I want you to let go. Ready? Let go. (slide whistle sound effect) Put your hands by your side and don't move. (laughter) We were pretty sure that would be safe, because of the conservation of energy. The ball started with potential energy, gained kinetic energy, and then came back with the same amount of energy it started with, minus a little bit that was lost through friction of the air. This doesn't have a whole lot to do with sports. 

But you know, it illustrates another principle. It illustrates the principle of an oscillator. There are many sports that involve that. When you're running, your legs swing back and forth, your arms swing back and forth. Have you noticed when they're speed skating, their arms are going like that. It's a little like a pendulum, isn't it? We're going to repeat this. Can you hold it by your nose again? Don't let go until I tell you. This time, we're going to time it. We're going to use our stopwatch here. When he lets go, I have already calculated that it should take between four and five seconds, maybe 4.5 or 4.6 seconds. 

You ready? Let go. (slide whistle sound effect) (laughter) Just about 4.6 seconds, just about what I calculated. Now, what do you think would happen if we replaced the bowling ball that weighs about 16 pounds with a softball that weighs about half a pound. Do you think it will take longer to go out and come back? Who thinks? Who thinks it will come back quicker? Who thinks it will come back in the same time? That's interesting. There's about an equal number of you that voted each way. Of course, in physics, we don't vote. That's for politics. And we don't just argue about things. We do the experiment. Two-thirds of you are going to learn something, right? (laughter) We'll repeat that. 

Let me restart the stopwatch. Whenever you're ready, let go. (slide whistle sound effect) Just about exactly the same 4.6 seconds, either way. So, that's true no matter what we hang on the end of the  pendulum. (musical flourish) (applause) It only depends on the length, and nothing else matters. So bowling, wouldn't that be the perfect sport for me, Peter? >> Actually, no. It's not a sport for you. You and I went bowling one time, and I remember your bowling score. It wasn't very good. But, you've lived here in Wisconsin for about 46 years, and we have ice skating here in Wisconsin. 

With your very extensive physics background, that should give you a great advantage. I found you your very own ice skater. Let's get him out here. >> I'm not coming. >> Why not? >> I need a proper starting announcer. >> Ah, a proper starting announcer. All right. Everybody's got to help me get him out here. On your mark, get set, go! (drum roll) >> Hi, there, Professor Sprott. >> Whoa! You're speedy. 

>> You're on the speed skating track there. If I'm going to teach you a little bit about speed skating, I guess we need an ice rink. Is there an ice rink somewhere in this physics building? >> No, we don't have an ice rink in the building, but I do have a way to make some ice. >> Okay, that sounds great. >> Just come over here. Here we have a little flask. It has some ordinary water in it. It's at the temperature of the room. Nothing special about it. Who knows the temperature water boils at? What? Perfect. 

100 degrees Celsius. Or in Fahrenheit? 212. Very good. >> That's right, isn't it? >> No, it's wrong. That's right only at sea level. If you go up on top of a mountain, water will boil at a lower temperature. And even in a city like Denver that's a mile high, water boils at about 94 degrees Celsius. So, it's a good answer, but it's not quite right. That suggests an interesting experiment. Suppose we reduced the pressure of the air above the water. 

Maybe we could lower the boiling point all the way down to where it will boil at room temperature. Shall we try that? >> Sure. >> Turn the vacuum pump on. >> Okay. Here we go. >> You see on the gauge, the vacuum is coming down near zero, and look what's happening. >> Wow, the water's boiling. That's really cool. But hold on, Professor. I thought I asked you for ice, not boiling water. 

>> That's right. Can you feel it and see how hot it is? >> Okay, I don't know. Is it hot? Actually it's really cold. And the whole thing is covered with ice all of a sudden. You can even see the ice crystals there. >> That's right. To boil something, you do need to heat it. And normally, you put something on your stove, and you heat it from the stove, right? We didn't have any source of heat here. But there had to be some heat. And the only place it could've come from is the water itself. 

Now, when you take heat out of something, the thing gets colder. Here, we took so much heat out of it, that it cooled down to the point where it froze. >> Huh. Oh! Professor Sprott, that reservoir is really hot. >> That's right. Energy is always conserved. It can only change from one form to another, or from one place to another. Here, the heat that we took out of the water down here ended up in this sulfuric acid up here. It's a trap that just keeps the water vapor from getting into the vacuum pump. >> All right, well now that we have some ice, let's talk about what we're going to do with you when we get you on ice skates. 

The first thing is we're going to have to know a little bit about Newton's three laws of motion. When we get you out there on the ice, you're not just going to all of a sudden go fast. You have to push. That's part of Newton's First Law, that says an object at rest tends to stay at rest, unless acted on by an outside force. Actually, a really good example is that Newton's Cradle that you're playing with right there. When one of the masses is stationary, it doesn't go anywhere magically. The other one has to knock into it and apply the force. You can see that when you have two masses the same size knock into each other, they move at the same velocity. That's because of conservation of momentum. Momentum is their mass times their speed. 

If you look at the one on the right, that shows what happens when someone much larger than you were to crash into you, say if you were being checked by a big hockey player. You move off at a much higher speed. That's because of Newton's Second Law, which says that the acceleration is inversely proportional to mass. In English, what that means is that if you weigh a lot less, and someone applies the same force to you, you're going to go off with more acceleration and more speed. And if you do the reverse experiment, where you have the little one knock into the big one, well, nothing much would happen. (screaming) Oh, hi, there, little hockey player. I hardly noticed you. >> I was trying to check you. But I guess I just don't have the mass to knock you over. But you know what? While I'm out here, I can show you guys some really neat stuff. 

You and Professor Sprott were talking about momentum, linear momentum in a line. I can show you all about angular momentum. >> Okay. >> So who here has been watching figure skating in the last few days? I see some hands out there. You've noticed how they can get going really fast in those spins. >> Yeah. >> Yeah? Well, let's show them here. I get up on this turntable here. Can you give me a little bit of a push. >> Sure. 

§ § >> So when you brought your arms in, you speed up. And when you put your arms out, you slow down. >> Exactly. That happens because of what's called the conservation of angular, or spinning momentum. When I start with my arms out, Marty gave me a push, and that gave me a certain amount of spinning energy. I can show you the same thing here, with these weights on the end of these bars. I give it a little push to get it spinning. And then as I pull them in so that they're moving closer to the axis of rotation, they speed up a lot, because that energy goes into making many little circles instead of just a few big circles. >> I think if you get back on that platform, we can show them something else. >> All right. 

Over here, you were talking about Newton's First Law, an object at rest stays at rest unless acted on by a force, and Newton's Second Law. I can show you something about Newton's Third Law here. I get up on the platform. I'll give the ball a toss. I start spinning. The reason I start spinning is that when I apply a force to the ball, the ball applies a force to me. That's Newton's Third Law, that for every action, there's an equal and opposite reaction. >> Can we try it the other way? >> Yeah, let's try it. >> So did everybody notice that as the ball came this way, Marty went that way? >> Yeah, but I went backwards a lot slower. >> That's because the ball has less mass than you. 

And that's Newton's Second Law again. Since Marty has more mass, less acceleration and slower speed, and the ball has more acceleration and faster speed. You know, Professor Sprott, after you get on the ice, and you know all about the collisions, and how you're going to start moving, why do we step on the ice in the first place? What happens when you step on the ice? >> I usually fall down right away. >> Right, because ice is slippery. Ice is slippery because there's not much friction on the surface of an ice rink. I can show you something a little bit like that with this soccer puck right here. If I put this soccer puck down on the floor and give it a push. >> That didn't do much. >> Doesn't do much, because the puck is in contact with the floor. And when two surfaces touch each other, they experience friction, which is a force. 

So what I can do is turn on a fan here that pushes on the floor and that lifts up the puck a little bit so that it doesn't experience much friction and this is the same to what happens with a hockey puck when it's on the ice. Give it a little bit of a push, and it really takes off, because there's not much to slow it down. This is another expression of Newton's First Law. Remember we said, something at rest stays at rest until you put on a force on it? Goes the same way with this, too. If something is moving, it keeps moving unless you put a force on it. I've got something else here to show you guys when it comes to surface area and things that are touching, feeling forces. I've got a couple everyday phonebooks, just like you probably have around the house. If I start layering the pages like this, getting a whole bunch of surface area, a whole bunch of surfaces that touch. >> Ella, this is going to take all day. >> But it's fun. 

>> For some people. (laughs) >> I have fun doing it, but tell you what. I won't make you guys sit there and watch me while I interweave all those pages. I've already done it with a couple of phonebooks. Can I get a hand from somebody? Let's see. How about you in the maroon right there? What we're going to do, is we're going to try to pull these phonebooks apart. Should be pretty simple, right? I mean, it's just two phonebooks on top of each other. What's your name? >> Angela. >> Angela, could you get a good grip on the spine of that phonebook there? You got it? Thank we can pull them apart? >> You can do it, Angela! >> Give it a hard tug. >> Pull as hard as you can. 

>> We're tugging on this hard, aren't we? And not much is happening. Let's give Angela a hand. Nice hard pull there. (applause) (musical flourish) The reason not much happened is the force of friction felt by each book due to the other book is huge, because of all that surface area that's in contact. there are thousands of pages, and they're all touching. So that's a lot of friction holding these books together. >> Let me try, just to make sure you weren't cheating. >> We don't cheat. We hockey players are just better. >> Ugh! That was uncalled for. 

>> It's just because I'm stronger than you speed skaters! >> You'd have to catch me first. >> I'll catch you! (whistle blows) >> All right, that's it! Penalty box for you! Get out of here! (musical flourish) (applause) >> Well, Professor Sprott, now that we got rid of that hooligan, I've been meaning to ask you. When I'm skating, I can go pretty fast. But is there some way that physics could maybe help me go even faster. >> How about if we give you a rocket? >> That's a great idea! Do you have one? >> Well, I just happen to have something that would serve as a rocket. It looks like a fire extinguisher, but it works on the principle of a rocket. When the carbon dioxide gas goes out that way, that's the action. You, holding the fire extinguisher, will be the reaction. >> Huh, Newton's Third Law again. >> Exactly. 

>> All right. I'll put on my helmet here. >> I would hope so. >> Okay, so if I shoot it that way, I'll go that way. This will really get me moving. How will I stop? >> I can stop you! >> Okay, sounds great. Perfectly safe. What could possibly go wrong? You might want to cover your ears though. Here we go! (musical flourish) (applause) (crashing sound effect) (laughter) (applause) >> Remind me not to go ice skating with you, Peter. >> Yep, that's right. 

Well, now that we've got those two mischief makers out of here, let's talk about sound and noise. How much do you know about noise? A little bit? A lot? Can you make a lot of noise? (audience yelling) Ella! Ella, Ella, Ella... What are you doing back here? >> Well, you were talking about sound. And they're here to learn about sports. >> Yes? >> And I figured that if you're here to learn about sports, and you want to make some noise, what better to do than to make a wave? >> Absolutely. >> Do you guys think you can do the wave? Yeah? You ready? Let's do it. >> Whoo! >> All right! (musical flourish) Well, sound is a wave, isn't it? >> Sound is one of many types of waves. In fact, I have some demonstrations of waves here. Here's something that we call a torsional wave. I give it a little twist here, and you can see that twist moves all the way down to the other end. 

When it gets here, it reflects and it goes back the other way. That's an example of a wave. I can do it again with an ultraviolet light here, with the room lights down. It's really pretty to watch these fluorescent stickers on the end. You can see the wave. (musical flourish) (applause) That's a torsional wave, a twisting. That's not what a sound wave is like at all. A better demonstration of a sound wave uses a gadget like this. Do you have one of these? It's a Slinky, right? Here, we have a long, straight Slinky that is suspended from strings from above. And what I'm going to do is stretch it on this end and then release it. 

That will make a wave that travels down toward the other end. Watch carefully. When it gets down to the other end, it reflects and comes back. And then the waves get all mixed up after a little while. But that's more what a sound wave is like. When I'm talking and you're listening, the air between my lips and your ears is going like that. It's compressing and it's expanding. But you don't see it, because the air is invisible. Even if the air were visible, you wouldn't be able to see it, because it's happening too fast. >> And I actually have another device right here that can also collect sounds. 

>> It's an umbrella! >> An umbrella? It does sort of look like an umbrella. Has anybody seen anything like this before? Maybe at a football game, where the guy at the sideline is standing and pointing into the football players so they can listen in to them? It's called a directional microphone. It's made up of two parts, a parabolic dish, or a concave surface, and a microphone. All of the sound waves are reflected off the inner surface of this dish and focused to the central focal point here, where there's a microphone. It can pick up sounds. Let's see if we can hear the person talking way back up there. >> Come on, seriously, that thing doesn't work. § Eee-lec-tricity... § Man, that thing is insidious. It gets in your head. Oh, wait. 

Is everyone hearing what I'm saying? (laughter) >> Ah, see? How about that clicking sound over there. Let's try that. >> I bet you could pick that up. >> To show how directional this is, I can pick it up if you watch the blue oscilloscope trace. Right there is my signal. If I move it left or right, or up and down, the signal comes and goes. I'll just stop right there, where the signal is at. >> You noticed that yellow trace up on the top. That indicates the sound that is coming out of the speaker. You notice just a little, brief pulse, way over on the left. 

And the sound he's receiving is over on the right. That means it occurs later in time. By measuring how far to the right it is, we can see how long it takes the sound to get from our speaker right here, over to his microphone. When he comes closer to the speaker, they should get closer together. It also gets a little louder as he gets over there. Then when he backs away, it will go the other way. This is a way you can actually measure the speed of sound. If we know the distance, and we know how much time that corresponds to, we can calculate the speed of sound. Does anyone know the number? How fast sound moves. What do you think? Anybody? 700 miles per hour, approximately, or 1100 feet per second, or about 340 meters per second. 

So, sound doesn't travel instantaneously. It's really fast, but not instantaneous. >> Professor Sprott, that sort of reminds me of when I was at a baseball game in Milwaukee this last summer. I watched the batter. He was at the plate. When he swung and he hit the ball, it took a little bit before the sound actually reached my ears. >> You must have had those cheap seats, way up in the bleachers. (laughter) >> Yes, I did. >> Baseball. Wouldn't that be the perfect sport for me? After all, I love hot dogs. 

That's a start, right? § § ("Take Me Out To The Ball Game")  (baseball being hit by aluminum bat sound effect) >> I got it! (musical flourish) (applause) >> Ladies and gentlemen, playing B Field for the H Bars, the magnificent Matt Miller! >> Hello, sports fans and physics fans. I'm really happy to be here today to teach you all a little bit about the physics of baseball. And first, I wanted to talk about the physics of batting. You probably noticed that when I caught that pop fly, that the ball flew in the path of a parabola. Actually, all balls follow parabolic arcs, because gravity acts on all objects, to accelerate them downward at the same rate. So it turns out that if you want to hit a ball as far as you can, then you should aim at a 45-degree angle. Just to show you that, I've set up over here, a spring-loaded cannon. And I have miniature sized "baseballs." We're going to load one of these baseballs into the cannon, like so.  I've aimed this cannon at 45-degrees to try to get the maximum possible range. Based on the exit velocity of this cannon, I've calculated that the ball should land in that far wastebasket. 

Who here thinks I can do my calculations correctly? Well, let's see. Three, two, one, fire! (musical flourish) (applause) How many people here have ever had a painful vibration in their hands after hitting a ball? Yeah? Well, that's because you hit the ball in the wrong place on the bat. I have a bat over here, suspended. What I'm going to do, is hit the bat up here. And what you'll see is the bat will wobble back and forth. Do you see how it's wobbling? That's what's causing the vibration in your hands. There's a sweet spot on the bat, which physicists call the center of percussion. If you hit the ball-- For this bat, the center of percussion is right here. If you hit the ball here, you will deliver the most energy possible from the bat to the ball. I'll strike the bat again. 

And this time, you'll see the bat swing like a pendulum. All right, here we go. See how nicely it's swinging? That's the sweet spot. I can also, if I hit it below the sweet spot, I'll get the wobble again. This time, it will wobble in the other direction. I'll steady it a little bit. See how it's wobbling again? So, the two things to remember, when you're up to bat, is to try and hit the ball at a 45-degree angle to get it to go as far as possible, and to hit it at the sweet spot on the bat, which for this bat, is right about there. Next, I wanted to talk about the physics of throwing. Professor Sprott, do you think you'd be willing to catch a ball from me? >> Sure, I even brought my glove just in case you asked. >> All right. 

I'm going to extend my arm and snap my wrist to try and get this thing going as fast as I can. Maybe you could measure the speed of the ball with that radar gun over there. >> Okay. >> All right. You ready? (musical flourish) (applause) Good catch! >> Two miles an hour. You must pitch for the Yankees. (laughter) >> It's a little hard with those wiffle balls. But it's true, I don't pitch as fast as those professional pitchers. But I can tell you how that radar gun works. You see, the radar gun shines out a beam of invisible light. 

And that light comes out in a certain frequency, and propagates as a wave, just like sound does. Well, when that light reflects off an object that's moving towards it, the reflected light comes back at a higher frequency. If the object is moving away, the reflected light comes back at a lower frequency. So, the radar gun measures the reflected light and compares it to the emitted light. It measures the difference in frequency and can calculate a speed from that. That change in frequency is an effect that physicists call the Doppler effect. >> Oh, yeah, I know about the Doppler effect. In fact, that occurs for any type of a wave, even a sound wave has a Doppler effect. I have here a ball that has inside a source of sound. If I turn it on, you'll be able to hear it. 

(high pitched tone) Hear that? Now, if I were to throw it toward you, the pitch would be higher. If I were to throw it away from you, the pitch would be lower. But that would happen pretty fast, so as an easier thing, I'll just spin it around my head. (pitch oscillates between higher and lower tones) The high pitch when it's coming toward you, and the low pitch when it's going away from you. But you know, there's something a little peculiar. It sounds perfectly normal to me. Why is that? I'm in the middle. It's not moving toward me. It's not moving away from me. That's the Doppler effect. 

That's how the police detect your speeding, with their Doppler radar. >> That's why I never speed. (laughter) I'd like to show you how to throw a curve ball. Professor Sprott, maybe you can demonstrate that by using that gadget right there. That will allow you to put a lot of spin on the ball. If you really whip it hard, you can get a nice spin. Try to throw it right at me, and we'll see if it-- >> Okay, but I'm not very good at this, so you'd better duck in the first few rows over there. >> All right. >> Whoa! (musical flourish) That was quite the curve ball. (applause)  Thank you. 

The way a curve ball works, is that as the ball is spinning through the air, it drags with it, air around. So on one side of the ball, the air is moving faster than on the other. That's what causes the ball to spin. It's an effect known as the Magnus effect. A very closely related thing is the Bernoulli effect. I can demonstrate the Bernoulli effect quite simply here with this piece of paper. I'm going to blow across the top of it. So again, we have fast moving air on one side of the object and slow moving air on the other side. What you'll see is the whole piece of paper will lift up.  Did you all see that? That's kind of what's going on with the curve ball. 

I do have one more demonstration of the Bernoulli principle. I've loaded up a whole lot of paper to the front end of this leaf blower. (laughter)  (musical flourish) (applause) You can go ahead and keep that paper! (laughter) >> I think they did that to my house once. Now I know how they did it. (baseball being hit by aluminum bat sound effect) >> Oh, geez, I better go catch that. Good luck finding a sport, Professor Sprott. Bye, everyone. (applause) (musical flourish) >> Well, you know, I did used to play baseball, but I got hit in the face with a baseball once and I had to wear a patch over my eye for about a week. It made me look like a pirate. (laughter) I don't think I want to do any sports that are going to hurt me. 

So how about something nice and tame. I used to be really good at ping pong. How about that? >> Ping pong? I'm very good at ping pong. All right, let's see if you can try to return my serve. See those cans right there? I'm going to try and knock them over, and you stop it. You did block it. That was pretty impressive, huh? (applause) Okay, I've got a different serve I can use. How about our pneumatic ping pong ball cannon? (laughter) The way that this works is there's a vacuum tube right here, and I have a vacuum pump hooked up to it. What I will do, is I will pump all the air out of it. There's a piece of tape at the end of that tube, and a piece of mylar on this end. 

After I remove all of the air from this, I will puncture the mylar on this end with a little pin. And what will happen is the 15 pounds of atmospheric pressure that we talked about will rush in and push against the ball, and we'll see what happens. You ready, Professor Sprott? >> Fire when ready, Ridley! >> Okay, I turned my pump on. Now I'm pumping all the air out of the tube. We call this a vacuum chamber. I've got my little gauge right here watching my pressure. The pressure is down, so I'll shut the pump off. Here comes my serve! (loud explosive sound) (musical flourish) (laughter) (applause)  Well, you weren't able to stop that one! I was able to knock the cans over that time. >> That's not the sport for me! I'm not going to touch that one. All right, all right. 

Let's do something that isn't going to hurt me. This is too dangerous. How about golf? What could possibly go wrong? >> I don't know. (thunder sound effect)  (electricity buzzing) (thunder sound effect)  (laughter)  (bicycle bell rings) § § § I want to ride my bicycle § § I want to ride my bike § (crashing sound effect) >> No, no, it's okay. It's okay. I was wearing my helmet. Professor Sprott, I heard you were looking for a safe sport. Have you considered bicycling? >> Yeah, that might work. >> Bicycling is a perfectly safe sport. Well, it's a perfectly safe sport, as long as you follow a couple rules. 

One, the rules of the road. Two, always wear your helmet. Who here wears their helmet every time they ride their bike? I see a lot of hands. And I like to see a lot of hands. You know why you wear your helmet? Because your parents tell you to. But do you know why your parents tell you to wear your helmet? They tell you to wear your helmet so if you fall, it helps protect you. And the way the helmet helps protect you is by slowing down a fall you have. So rather than hitting something hard, like the floor here, you'll be hitting something softer, kind of like Jell-O. And if an impact takes a longer amount of time, it hurts you less. I've got a demonstration about this. 

I have here a human head analogy. (laughter) A little egg-head, if you will. You can consider this the control experiment. If I take this egg and drop it, we can all guess what's going to happen, right? I make omelets for dinner. Now, instead we've got something to slow down the impact. Let's say we take some of this foam. This foam is a lot like the inside of your helmet here. If you take that instead and wrap it around the egg, and I hope your helmet is held together by something other than duct tape. (laughter) Now, I always like to put this out as kind of an option here. Who thinks this is actually going to work? A show of hands. 

Who thinks that it's not going to work, and it's going to break the egg? Well, as it has been stated, in physics, we don't just argue about things-- No, don't get me wrong, we do argue about things! But then we like to do the experiment to show who's right. So, let's see whether or not this will break. Remember, avoidance is the best policy, anyway. All right. We open this up. You can see... The egg has survived. (musical flourish) (applause) So please remember to always wear your helmet, because your head is a lot like an egg. But yeah, cycling is a really safe sport. I mean, back when I was a kid, I used to think how can it possibly be a safe sport, you're riding around on two wheels, and that's not stable at all, which is why I had training wheels until I was 23. 

(laughter) But no, we know you can do it, right? We see people doing it all the time. And who knows why you can ride around on two wheels? Say it out loud. Balance! Balance is a very, very important part of it. But there's actually a few tricks about a bicycle that can help you stay upright. I think I'm going to talk a little bit about them. First off, have you ever looked at the front of your bicycle, at the front fork here? Obviously, they don't go straight down. They actually jut out to the front. And the reason for this is, because they jut out to the front, if you start falling to one side, because they're forward of the axis, the wheel will turn underneath you and help pick you up. If you fall to the other side, it'll turn here and help pick you up. And you can kind of think about this when you're riding your bike really slow, how you kind of wobble a little bit to the sides, but you always seem to stay upright. 

It's your wheel turning underneath you. This is a type of dynamic stability. You can think of it sort of like you're a little ball sitting in the bottom of a valley. If you go off to one side, you kind of roll back to the center. It's the same thing that helps you with the bicycle at low speeds and at high speeds, but it's more pronounced at low speeds. This next effect I'm going to talk about has to do with the bike wheels themselves. The bike wheel is not filled with any sort of special material, unless you consider air a special material. And you know, if you drop it, it's going to fall. However, when you get the bike wheel spinning kind of fast-- Professor Sprott, can I get you to help spin this up? >> Sure. >> When you get this bike wheel spinning fast, you'll notice that it doesn't want to fall when I let go of it. 

Instead, what it wants to do is process, like a top. A top is a toy that we used to play with back before we had the Internet. (laughter) But yes, it will process around its axis instead of falling down, which, when you're traveling at high speeds, is one reason that you can stay up on your bike. Which brings me to my last demonstration over here, this bike. Before I talk about this bike, I'm going to bring up an idea that Professor Sprott has already talked about. Energy. He talked about the conservation of energy with the bowling ball over there. When it was high, it had a lot of potential energy. When it was low, it had a lot of kinetic energy. And when it was high, it had a lot of potential energy again. 

This bike uses a variety of different types of energy, and some new ones. So, it starts off with chemical energy. That's the energy that I have from eating Twinkies backstage. (laughter) I'm going to turn that into mechanical energy by spinning around the wheel here, and this back wheel is going to turn. This is hooked up to a generator, which will spin a magnet. That will create electrical energy that runs through these wires up to these lights, which will then use that energy to heat up. They'll have heat energy, but they'll also produced light, so radiant energy, a different type. This is a complex way to turn Twinkies into light. (laughter) All right, before I get started, I should probably point out that each of these bulbs is 20 watts. I have five of them, that's something like 100 watts, so this is like riding up hill a bit, so you'll excuse me if it takes a little bit of energy to get this going. 

 (musical flourish) (applause) I'd also like to apologize to anyone in the front row who smells burnt rubber. Speaking about that, I said that these were 20-watt bulbs. If I had replaced these with some compact fluorescents, I could've made that much brighter, because more efficient bulbs means it's easier for us to get light, instead of spending a lot of energy, either on a bicycle or down at the power plant. Speaking of energy, I'm about out of it. And I should let you get back to looking for a sprott, Professor Sport. (laughter) I mean-- eh, whatever! (applause)  >> Well, you know, I do ride my bicycle a lot. But about five years ago, I was riding along and I came to a curb, and I figured I'd just bump up and over it. How hard can that be? But I went right over the handle bars and landed face down on the concrete. I went over to the hospital and they fixed me up. The next day, I came in to teach my class, right, in this very room. 

I had this bandage on my forehead. And I thought I'd better explain to the students what I did. So I told them. Then I said there are three things I learned from this. One, always wear your bike helmet. Well, I did have my bike helmet, but I guess it was a little too far back on my head, so be careful about that. The second thing I learned, don't do stupid things. (laughter) Well, okay, I'm one for two. But the third thing, I said always be good to your students, because the doctor who stitched me up was a former student. (laughter) And your worst nightmare is to be a professor, and you go to the emergency room, and have one of your students there to fix you up who wasn't very happy with the course they took from you. 

Anyway, bicycling is a nice sport, but it's sort of fast, it's potentially dangerous, it needs special equipment, like a nice bicycle. Isn't there something that doesn't require all this special equipment, and doesn't go quite so fast? Something like running? >> Ah, running, yes. You know, this last year, I was at the triathlon, and I ran into a very rambunctious runner that was there. I was able to convince him to come visit today. So, I introduce to you, Dr. Sport. (applause) >> Well, hello, everybody. I'm Dr. Sport. >> Dr. Sport, Dr. Sprott. Dr. Sprott, Dr. Sport. >> Dr. Sport. 

>> Pleased to meet you. It's an honor, Dr. Sock, I wear your invention every day. It's like a little mitten for your feet. I love it. It's a pleasure to meet you. >> No, it's Sprott, not sock. >> Ah, I see. Well, what do you do? >> I'm a professor of physics. >> Ah, a professor of physics. I'm a professor of sprinting. 

>> Hmm, never heard of that. >> You've never heard of sprinting? >> Well, I've never heard of a professor of sprinting. >> Ah, I'm a very special person. I weigh 800 pounds. >> I don't think so. >> Well, I can prove it. Do you have a scale? >> Right over there. We happen to have a scale. >> Do you mind if I jump on your scale? >> Go for it. >> Thank you very much. 

>> It's a little like a bathroom scale, but ours is a little special, because it's connected to a computer. You can not only see what the reading is , but you can see how it changes in time. It's a little bit unusual and special. >> All right, I'm going to jump on your scale. Here we go. Yee-ah! (musical flourish) (applause) 900 pounds! I love your chocolate plasma. Do you have any more of that chocolate plasma? >> You haven't been eating our plasma, have you? >> It's so good. Those, and the yogurt-covered electrons. I do love your yogurt-covered electrons. >> No, you don't eat plasma. 

That's silly. >> Well, back to sprinting. There you go, 960 pounds. >> But that's not your weight. That's the force the scale is pushing up on you with. Your weight is the force that gravity is pulling down on you with. >> You mean that this scale doesn't measure the weight? >> No, only when you're perfectly still. If you're moving, the two are not equal. >> I thought the scale measured weight. I'll have to stop listening to Oprah. 

(laughter) I can tell you, though, that if you want to be a good sprinter, you have to be able to tip the scale at least 800 pounds. What do you think you gets you down the track? >> Well, I guess the force of the ground on your foot. >> Yes, the force of the ground pushes up on your foot. That's right. Would you like to see if you have what it takes to be an Olympic sprinter? >> Yeah, let's do that. >> All right. Let's go right over here to the start line. >> Okay! >> And you know what those sprinters do, right? >> No, what? >> You get down in a crouch like this, and then I say, "Ready, set, go!" I want you to run as fast as you can and step on that platform. >> Okay, I'm ready. >> On your mark, get set, go! (musical flourish) (applause) Well, look at that! 900 pounds. 

You know, it really is the up and down force that's important. If we can have Mr. Starter show us the sideways force, the sideways force is much smaller. It's barely 100 pounds. The important force is really in the up and down direction. But I see that you can give 900 pounds, so would you like to be in the Olympics? >> Yeah! >> All right, fantastic. We've got just the sport for you. >> Okay! >> Let's go back to the starting line. >> Okay! >> You know we've been having a problem with our ratings? We're going to lose a lot of money this year. We need to make our sports more exciting for people to watch on TV. >> That's me. 

>> Our new sport is going to be the 20-meter dash. >> Okay! >> So, I want you to get down into that start position. And when I say, "Ready, set, go," I want you to run as fast as you can, straight into that wall. >> Hey, wait a minute! >> Ready, set... >> Wait, wait, wait! >> Go! >> No! Wait a minute! Just because I'm a professor, I'm not going to run into that wall. I'm not stupid. >> Oh. Well, Professor Sprott, I guess you won't be going to the Olympics in sprinting then. Good luck finding a sport, Professor Sprott. I know you can do it. 

Goodbye, everybody. (musical flourish) (applause) >> You know, I do run in the Crazy Legs Classic every year. There's about 9,000 people that have better times than me. (laughter) So I don't think that's going to work, either. Maybe I better just stick with physics. But I hope we've convinced you that there's a lot of physics in sports. And understanding the principles of physics will make you a better athlete. So, if you're interested in sports, that's good. You should find a sport that you're interested in, and work hard to get good at it. But understanding the physics will help you be a better athlete. 

Maybe physics should be an Olympic event. In fact, there is a Physics Olympiad. It's in its 41st year. It's for high school students. This year, it will be held in Croatia, in July. Maybe some day, some of you could be in the Physics Olympics and win some gold medals, like I have never been able to do myself. But I'd like to conclude the show the way we've concluded every one of the 221 shows that preceded this, by making for you a cloud. We do that using liquid nitrogen. And nitrogen is normally a gas. You're breathing nitrogen right now. 

About 80% of the air you're breathing is nitrogen. But if you cool it to a temperature of 321 degrees below zero, it turns into a liquid. And we have a large container with the liquid nitrogen. We force nitrogen gas into it. That forces the liquid up into this pipe, where it comes out these holes in the top. And it cools the air, because it's still very cold. The water vapor in the air will condense into tiny droplets of liquid water, each about 1/1000 of an inch in diameter. That's what we call a cloud. And so with that, I will put on my hat, and thank you all for coming. § § (applause)  § § (applause continues)