Newton's Apple; No. 701

<v Speaker 1>Newton's Apple Show, 701. Total time twenty seven forty KTCA-TV, St. Paul, Minneapolis. <v Speaker 1>Join us as we plunge into this season's first Newton's Apple, we discover the science behind the terror of roller coasters, narrowly escape the clutches of quicksand and wrestle a ferocious wild tiger. All of this and more on our season premiere. <v Speaker>[theme music] <v Speaker 2>Welcome to Newton's Apple. Newton's apple is made possible by a grant from Dupont, makers of Better Things for Better Living and also by public television stations and viewers like you. And now your host, science correspondent, David Heil. <v David Heil>Thank you. Thank you very much. Welcome to another season of Newton's Apple. If you wonder about nature, technology or the human body or if you're just curious about the world around you, that's why we're here. From bee stings to boas, from volcanoes to spider webs. We'll answer more of your science questions this season on Newton's Apple. So let's go right to this first question of the season comes from ?Adam Baker? Of Lebanon, New Jersey, who asks, Why does your stomach tickle when you go downhill in a roller coaster? You know, I can think of a few words besides tickle to describe a roller coaster ride. But in order to answer Adam's question, we sent our fearless field reporter, Peggy Knapp, to the Great America Amusement Park in Santa Clara, California.

<v Peggy Knapp>Ah, amusement parks, the cotton candy, the games, the rides, the nausea. I don't like rides any rides. They make me nervous. And not only that, they make me sick. So, of course, what did I have to ride on? Oh, no, no, no. Not the racing snails. I had to ride on something called the demon. It goes upside down. My guide for the day into the stomach churning physics of roller coasters was ?Don Rathjen?, a physics teacher at Foothill High School in Pleasanton, California. So this is exactly the kind of ride where I feel like I'm just going to lose my stomach and my lunch. <v Don Rathjen>Well, it's understandable.

<v Peggy Knapp>Why is that? <v Don Rathjen>Well, if you think about going off the top of the ride, we have mass, and that's associated with inertia. That means we tend to keep going wherever we happen to be going. Something has to redirect us. And if you come off the top of that hill and the car is going down on the track and you tend to go out straight, you could fly right out of the car. <v Peggy Knapp>Fly right out of the car. <v Don Rathjen>But you got that harness there to keep you coming down. And so you're always sort of in between the seat and the harness. You're off the seat, not completely off, but lighter. And so everything inside here feels pressed together a little differently than it normally does. And that's--. <v Peggy Knapp>Your brain says--. <v Don Rathjen>Your brain says--. <v Peggy Knapp>You're losing your stomach. <v Don Rathjen>That's it. <v Peggy Knapp>While you experience a certain degree of weightlessness over the peak of the hill, you experience the reverse at the bottom. Your inertia is now directed downward, but the cars and the roller coaster are being redirected up the next hill. So for a moment, your body is traveling down. The cars are coming up underneath you and you feel pressed into your seat. This squashed feeling is so much fun that they figured out a way to measure it. <v Don Rathjen>This is called an accelerometer. And notice that there's a fishing weight here. If you are holding this thing when the coaster comes up underneath here.

<v Peggy Knapp>And you have the presence of mind to look at it. <v Don Rathjen>Look at it. Well, the fishing weight has its inertia and it wants to keep going and the rubber band stretches. And if the fishing weight gets all the way down to-- if the fishing lake gets all the way down to two, then that means you'll feel like you weigh twice as much as you normally do if you're sitting on a bathroom scale. That's what it would show. And we call that a 2 G-force. <v Peggy Knapp>What about the curves? Why do I get slammed into the side of the car and feel like I'm going to pitch right over the edge? <v Don Rathjen>Well, I'll think about it being in a car, regular car. You're going around a curve, taking a right turn. You may feel like you're thrown outward against the door, but if somebody is up top looking down at you, they'll see your body with its inertia going straight ahead and the car's coming over and really redirecting you into that circle. <v Peggy Knapp>What's pushing you and the car into the curve is something called centripetal force. It's the center seeking force that all turning objects experience. And since I was soon to become a turning object, I guess I was going to experience it as well. You know, they want me to ride one of these things. <v Don Rathjen>Well, we come back tomorrow and you could even try the accelerometer.

<v Peggy Knapp>That's great. They're closed tomorrow. <v Don Rathjen>Oh, so much the better. Then we can have it all to ourselves. <v Peggy Knapp>Oh, boy. Understanding the physics of what my body was about to go through somehow didn't make me feel any better, so I decided to find out how rollercoasters work. ?Dana Morgan?, a roller coaster designer in Scotts Valley, California, took me 100 feet in the air for an explanation. Good thing I don't have a problem with heights. <v Dana Morgan>What happens is that this chain that we see right here is powered by an electric motor at the base of the limb. The train engages this chain with the chain dog and it's raised to here adding potential energy to the train. <v Peggy Knapp>And then what happens after here? <v Dana Morgan>It goes over the top of this lift beyond where the chain ends. And from there on back, it's gravity. <v Peggy Knapp>It's just rolling after that. <v Dana Morgan>That's correct. <v Peggy Knapp>Coaster rides a roller coaster. <v Dana Morgan>Exactly.

<v Peggy Knapp>The first hill or the lift of a roller coaster is its highest point. This is the only place where energy is put into the ride by the motor and chain. At this point, the cars are poised at the top of the hill with potential energy because they're in a position to fall downhill. Now gravity takes over and the potential energy is converted into kinetic or moving energy. <v Dana Morgan>Now we've gone back up high again and fairly slow because we're almost as high as the top of the lift. <v Peggy Knapp>Almost as high? <v Dana Morgan>Exactly. We can never go as high again as the top of the list. <v Peggy Knapp>Why is that? <v Dana Morgan>Because we don't have enough energy to go any higher than the first. <v Peggy Knapp>Oh, I see. The exchange of potential and kinetic energy continues up and down each hill for the rest of the ride, the cars slowing down as they gain energy and speeding up as they expand it. At the same time, the cars are losing some of their total energy to wind drag and friction, which gradually slows them down. So the whole ride really is balancing those factors. Gravity, acceleration, deceleration, friction, wind drag. <v Dana Morgan>Exactly. It's-- it's a giant energy equation, really. And it's balanced such that when the train returns to the station, there's just enough velocity left that the brakes will stop it coming into the station.

<v Peggy Knapp>It was all making sense. But there was just one more question I wanted to ask. Why doesn't the car fall off the track? <v Dana Morgan>That's a very good question. <v Peggy Knapp>It's a very good question. <v Dana Morgan>The train has three sets of wheels. It has road wheels very much like those on an automobile that it runs on. It has guide wheels that are sideways and they steer it so they cause it to come around the corners. The third set of wheels are called up stock wheels. They are underneath the track and they keep it from coming off the track. Those are particularly necessary on a ride that goes upside down. <v Peggy Knapp>Yeah. Yeah. So it's perfectly safe. <v Dana Morgan>Absolutely. <v Peggy Knapp>All too soon, the big moment arrived, just remember, three sets of wheels, absolutely safe people pay money to ride this. <v Don Rathjen>This is ?Steve?. He's a fellow physics teacher.

<v Peggy Knapp>Nice to meet you. <v Don Rathjen>Here's your accelerometer. <v Peggy Knapp>Accelorometer. OK. <v Don Rathjen>Climb on in there. We'll get your harness fastened. There you go. OK, Steve, you're in there. <v Peggy Knapp>Are you gonna get in the back there? <v Don Rathjen>Oh, Peggy, I never ride these things, I get sick on these. <v Peggy Knapp>What do you mean you get sick on these? <v Don Rathjen>Have a good trip. See you later. Have a good hill for me. <v Steve>Have you ever ridden one of these before? <v Peggy Knapp>No, I've never ridden one of these things before! <v Steve>Do you know what we're doing right now? <v Peggy Knapp>We're climbing an enormous hill! <v Steve>No, we're gaining gravitational potential energy. <v Peggy Knapp>Oh, I see. That's fascinating. <v Steve>What happens when we get to the top? <v Peggy Knapp>Well, it looks like we're going to go down. <v Steve>Yes. We gain kinetic energy which is the same as--. <v Peggy Knapp>Motion. Veloci--. <v Steve>Velocity. <v Peggy Knapp>Speed. <v Steve>Speed, yes. <v Peggy Knapp>When do we look at these things? <v Steve>Well, we'll look at these accelerometers when we get to the bottom of the first hill. <v Peggy Knapp>This hill? <v Steve>Yes, we're rested to our seats. OK, ready? Here we go. <v Peggy Knapp>[inaudible]. <v Steve>It's reading three Gs now.

<v Peggy Knapp>Three? Oh, my gosh. <v Steve>And now, you know, we've gained a lot of kinetic energy which is a good thing otherwise we'd fall out of our seats! <v Peggy Knapp>That'a a heck of a thing to be saying to me right now! Will we get any more kinetic energy now? <v Steve>A little potential energy there. <v Peggy Knapp>What's that? <v Steve>That's the corkscrew. <v Peggy Knapp>The corkscrew! <v Steve>The corkscrew. That's right, and in the corkscrew, we'll be experiencing centripetal force. <v Peggy Knapp>Fascinating, Steve. Centripetal force! <v Steve>As we experience the centripetal force, it keeps us from falling out of the rollercoaster! <v Peggy Knapp>That's great! <v Steve>Got 2 G's on that. <v Peggy Knapp>And then it was over. I didn't feel great, but at least I didn't. Well, you know. Oh, there's Don. Hi Don! <v Don Rathjen>Hey, welcome back. How was it? Steven. <v Peggy Knapp>Oh, thanks. Thanks so much, you guys. I had such a great time. <v Don Rathjen>Hey, where are you goin-- where are you going, Peggy? <v Peggy Knapp>I think I'll rest a minute.

<v Don Rathjen>Just remember physics is fun. <v Peggy Knapp>Fun. And this from the man who wouldn't ride it. <v Don Rathjen>We'll do it again sometime. <v Peggy Knapp>Sometime. <v Peggy Knapp>I'm going home. <v Speaker>[transition music] <v Voiceover Artist>More party trivia, fascinating fact number three hundred and forty two frogs, frogs have to look before they leap. Once in the air, they are unable to see. At take off, the frog uses muscles to pull both eyes back into their sockets, protectively closing the lower lids over the delicate eyes. But a tree frog doesn't have to leap. Lands on the pads of its feet secrete a sticky substance that allows it to climb instead. <v Speaker>[transition music] <v Tarzan>Where's Boy?

<v David Heil>Anyone who has ever watched a jungle adventure movie may get a sinking feeling when they hear the word quicksand bubbling pits of sand that pull villains down into the earth. That's probably what ?Shane Barclay? Of East Northport, New York, was thinking of when he wrote us this letter and asked us what is quicksand and how does it form? Here with the answer is our very own jungle physicist, Jearl Walker, author of The Flying Circus of Physics. Welcome, Jearl. <v Jearl Walker>David. <v David Heil>You've got me all dressed up in my jungle attire here. I suppose you're going to tell me we've got real quicksand in the studio. <v Jearl Walker>As a matter of fact, we got two collections of quicksand here. <v David Heil>Of real quicksand? <v Jearl Walker>Real quicksand. You're not afraid of quicksand, are you? <v David Heil>Of course I'm afraid of quicksand. I saw those Tarzan movies as a kid. I used to be worried about walking through the woods at night. <v Jearl Walker>You have nothing to worry about. Physics will save you in the case of a quicksand. Let me show you the physics over here. <v David Heil>All right. <v Jearl Walker>What quicksand is. Most people don't understand what quicksand is. <v David Heil>This isn't quicksand, is it?

<v Jearl Walker>No, no. This is just normal wet sand. <v David Heil>What it looks like. <v Jearl Walker>But if we wanted to make this quicksand, we would have to supply one additional ingredient. We would have to make the water force its way up, like from some underground spring or something like that. <v David Heil>So that makes it quicksand. <v Jearl Walker>That's right. Let me turn on some water pressure by increasing a pump down here. And look. <v David Heil>Look, it's getting wetter on top here. <v Jearl Walker>That's right. <v David Heil>Oh, the house is sinking. <v Jearl Walker>The water is being forced up. <v David Heil>Oh, look at this. An apple. Here, Jearl. <v Jearl Walker>Notice the house. <v David Heil>The house is just disappearing here. <v Jearl Walker>It's on its way down. <v David Heil>So now the house sinks, but this apple bubbles up to the top. Why is that? Would the house eventually come back up as well? <v Jearl Walker>The House would never come back up because it is denser, because we've added some weights to this little model house. It is denser than this fluid of water and sand quicksand. At least when we had the pressure on, I've turned the pressure off and we're going back down to just normal wet sand like-- <v David Heil>Trapped this. Look at this house we can't even budge this thing.

<v Jearl Walker>That's right. It's quite stuck because the sand is no longer being forced upward. Very dense object denser than the sand water mixture will sink. A very light object such as this apple will float to the top. <v David Heil>So just like the apple would float in regular water without the sand, it's going to float in this fluid mixture. <v Jearl Walker>That's right. And as a matter of fact, you would float in quicksand in a way very similar to the way you float in water. <v David Heil>Wait a minute that's not the way I remember it. Those guys disappear pretty fast. They, like, get pulled right underneath the surface. <v Jearl Walker>Well, they take certain liberties in movies. Come over here. Let me show you the same physics on a grander scale. <v David Heil>All right. <v Jearl Walker>Just for a moment think of this as a large sand grain, OK? <v David Heil>Very large. <v Jearl Walker>Very large sand grain. I would like to levitate that, suspend it, kind of like over the same grains over in the pit over there. But I can't use a water stream or I'm just make a big mess. What I'll use is air. And I push this button, I get an airstream. <v David Heil>So I put this on the airstream?

<v Jearl Walker>Yeah. Shooting up and there it goes. It's suspended. And there's fluid this time air, but it's kind of like water over there. The fluid is pushing the sand grain make-believe sand grain upward and levitating it. In fact, you can even rock this over by an appreciable angle [inaudible]. <v David Heil>And it still keeps it levitated. So the water moving around all the sand grains in this tank keeps them all suspended. And that's what makes quicksand. <v Jearl Walker>That's right. As you can see here, when the water pressure pushes up all the sand grains, lifts them up, then they move away from each other. They no longer touch each other. There's no longer any friction between them. And now if we put something reasonably dense on top, it has the chance of sliding down into the quicksand. <v David Heil>Through all these little spaces that have been created. <v Jearl Walker>That's right. Something like if we were to put you on quicksand, you would slide down into all these little sand grains. <v David Heil>Jearl, you keep bringing this idea for putting me in quicksand. Now, wait a minute. As much convincing as you've done, I still envision myself sinking into this bottomless pit of quicksand. <v Jearl Walker>No, no, no, no, no. David, if you were to go into quicksand, you would just sink in a little ways, just like the apple, and then you'd kind of float.

<v David Heil>I still need more convincing. <v Jearl Walker>Well, let's take a little walk up the hill here. <v David Heil>We're getting into the jungle for this one, huh? <v Jearl Walker>Proper attire. <v David Heil>I suppose you're going to make me go first. <v Jearl Walker>Well, you are the host. <v David Heil>All right. <v Jearl Walker>And what we got up here is a big vat of sand. Yeah. Wet sand, though, that's all. And it's very firm and stable. And I'd like for you to step onto it. <v David Heil>So this is safe, huh? <v Jearl Walker>I don't know. <v David Heil>Wait a minute, Jearl. <v Jearl Walker>But we'll know for sure when we turn the water on. <v David Heil>What kind of hesitation is that? So we're going to percolate water up through this. Wait a minute, Jearl. I can feel myself going down. <v Jearl Walker>Oh, well, the water's coming in. The water pressure is coming up. Boy, this is exciting. <v David Heil>Guarantee me a bottom on this thing, all right? <v Jearl Walker>That is just great. <v David Heil>It's cool. It's not quite tropical. Oh, this is weird. <v Jearl Walker>You're sinking right down out of view. <v David Heil>Yeah, that's very good, Jearl. Didn't take physics to figure that out. Oh, this is amazing stuff. It's just all around me. Oh. And if I do move it really loosens up.

<v Jearl Walker>One might wonder just how far are you going to sink down. <v David Heil>I thought you said this wasn't bottomless. <v Jearl Walker>No, no, no. Trust me on this. Trust me, you're going to sink down just so far and then you get enough buoyancy to float just like that apple did. You're going in deeper than the apple. But see, you're floating. <v David Heil>The sand just keeps moving up around you too. Jeryl, if I were running through the woods and really fell into some of this, not in a controlled situation, like, I hope this is, how would I get out? <v Jearl Walker>Well, I think the first rule to follow is don't panic, because if you suddenly try to pull your legs out, the quicksand is going to hold onto you all that much more. <v David Heil>Well, you've got to admit, it's a natural tendency to think that this is-- actually I can't pull my legs out anymore. <v Jearl Walker>What you need to do is to lie back on the quicksand and gradually pull your legs out and then you can roll over to the shore and escape. <v David Heil>Float on my back in quicksand. <v Jearl Walker>Yeah. <v David Heil>That's the technique for getting out. <v Jearl Walker>Right. <v David Heil>That's the official technique. I can't do it here. There's not enough room. <v Jearl Walker>Oh.

<v David Heil>So how am I going to get out of this one? <v Jearl Walker>How about the traditional manner? <v David Heil>Like what? <v Jearl Walker>The vine. <v David Heil>I knew I could count on you, Jearl. Oh, if I could just get out of this quicksand, we'll be right back. <v Speaker>[transition music] <v David Heil>If you have a science question you'd like answered by Newton's Apple, write us, send your questions to Newton's Apple Box. Nineteen eighty three, St. Paul, Minnesota, five five one one one. Remember, our show depends on your questions,. <v Peggy Knapp>Jelly.

<v Bob>Watch it. Ew, why does it always land jelly side down? <v Peggy Knapp>I'm really glad you asked me that, ?Bob?. What a mess. And it's all thanks to physics. A peanut butter and jelly sandwich that falls off the edge of your counter will land jelly side down every time. Well, almost every time now. You're probably thinking it's because the side of the bread that has the peanut butter and jelly on it is heavier than the side without the-- the empty side, well, it's a good thought, but it's not exactly how it works. Let's have an instant replay. As I accidentally pushed my peanut butter and jelly sandwich off the edge of the counter. It doesn't fall straight down. As it approaches the floor, it starts to spin. Unfortunately, it only completed half a turn before it blocked onto my clean kitchen floor. The key to this mess is spinning. How fast it spins depends on how big the bread is, the bigger the bread, the slower the spin. Now, most bread, in fact, most of the things that you're likely to find on a kitchen counter spin at about the same rate like this if I spread peanut butter and jelly on this book. There you go, and accidentally shove it off the edge of the counter. It lands jelly side down, also. Bread has to be this small in order for it to have enough time to make a full revolution and land on the floor jelly side up, but I got to eat like twenty five of them before I can call it lunch. Now big bread will also land jelly side up, but it's got to be about two feet across and you'd have to special order that. There is, however, a solution to the problem of the average sandwich. All you really need is a taller kitchen counter in your kitchen counter is, say, only 10 feet above the ground and your peanut butter sandwich accidentally slips off the side. It does have enough time to make one complete revolution and thus will land jelly side up every time. I just love doing research. <v Speaker>[transition music]

<v Voiceover Artist>Was that a raindrop? Not to worry, there are no soggy feet in this forecast. These compact little slippers fit comfortably over your shoes and ankles. Two quick zips and they have you covered. But best of all, these pristine puddle protectors are transparent and can weather any wardrobe challenges. Now, what are these beauties up to? Why it's the latest twist in exercise. Waste away unwanted inches. Just step on the disc and rotate your way to a slimmer figure. Looks like these gals will be spinning their way into the newest dance craze. Oh my, the secretary's dream. Double your workload with this little setup, with this clever system, you can manage a call in each ear, a letter for your boss and never one lose your pencil. Now, if we could just rig the coffee box to a foot petal. <v David Heil>Our next guest acts like a tiger, growls like a tiger, but doesn't quite look like a tiger. Here to help us understand why that is is naturalist Nancy Gibson. Welcome, Nancy.

<v Nancy Gibson>Thank you. <v David Heil>Now, this does not look like a normal orange tiger that you think of when you think of tiger. Now, what's the deal? Is this an albino? <v Nancy Gibson>Well, it's not an albino because albino means it's a lack of color or pigment. And, you know, she's got beautiful blue eyes and she's got sorta the brown stripes on her. And you can see she's a pretty good jumper, too. She's a white Bengal tiger from India. And but her home right now is at the Columbus Zoo and she's about four months old, named Lily. <v David Heil>Lily White. OK, now were both of Lily's parents white and that's why she ended up being white? <v Nancy Gibson>Yes, both of her parents were white. But just to confuse the issue a little bit, all of her grandparents appeared to be that standard orange color. <v David Heil>And how does that work? <v Nancy Gibson>OK, well, I'm going to give you a little lesson in genetics. <v David Heil>OK, I'm ready. <v Nancy Gibson>OK, the color of a tiger is determined by a pair of genes. A cub receives one gene from each parent. Now, the two trade options are the standard orange color and white. In this case, the orange color is dominant and the white is recessive. The orange will always dominate over white, so the tiger may appear that standard color, but carry the white gene. So recessive means that both genes have to be white in order for the cub to be born white. <v David Heil>OK, so in Lilly's case, there's pretty much a guaranteed outcome since her parents were white, the only gene she could get from them was that recessive white gene.

<v Nancy Gibson>We're going to keep her calm. I'm going to have to give her a little bit of that. <v David Heil>All right. You just go ahead and do that. And she definitely wants it. <v Nancy Gibson>Yeah. <v David Heil>You know, in the wild, a white tiger would not be very camouflaged. And so when they're trying to hunt, they can't hide behind yellow or brown bushes. <v Nancy Gibson>Right. Well, that's certainly always been the standard theory. But when you really look into it a little bit further, you'll notice that or you probably know that the prey species don't see in color. So they can still see the stripes, but it wouldn't really matter as to what color. Also, tigers are nocturnal hunters. So I don't think being a white color really makes that big a difference. But it had-- they have determined that white tigers do have some problems with their eyesight. <v David Heil>Oh, it's part of the genetic inherited white color? <v Nancy Gibson>Yes, come over here. Let's see if we can-- <v David Heil>She likes that bottle. <v Nancy Gibson>You want to try feeding her? <v David Heil>All right. I'll give it a try. <v Nancy Gibson>OK. <v David Heil>Here, it's over here. Here, right here. There it is. <v Nancy Gibson>[inaudible] <v David Heil>All right. She says, I want to make sure it's there.

<v Nancy Gibson>Right. <v David Heil>I'll take care of the bottle. <v Nancy Gibson>Okay, there you go. <v David Heil>Now, what kind of animals do they hunt? <v Nancy Gibson>Well, they have a variety of prey. There are some wild cattle and wild pigs and deer and antelope that they like to pounce on. But the main thing about tigers, in order for them to survive, they have to have adequate cover. And they live, as I said, in the different regions of northern India. In order for them to hunt, they have to be able to stalk or sneak up on their prey and they'll get to, say, within several yards and using that very important cover, then they'll pounce or strike on top of their prey. <v David Heil>Really? So that's what these big paws are all about, huh? <v Nancy Gibson>Well, she's also going to be a big tiger. Another interesting thing about white tigers is that they are actually a bit larger than the standard colored ones. <v David Heil>How big? <v Nancy Gibson>She's going to weigh about 350 pounds when she's full grown. <v David Heil>That's plenty big. Yeah, I'm glad we've got her on the show now. <v Nancy Gibson>Right. Me too. <v David Heil>You know, when you talk about that hunting situation, what kind of range are they hunting over? <v Nancy Gibson>Well, the males actually have quite a large range. I think it's like 40 square miles that they-- or square kilometers that they need. <v David Heil>That's significant.

<v Nancy Gibson>The female's is actually a little bit smaller, but they need to have that wild habitat and a good source of prey. <v David Heil>They miss on occasion so there've gotta plenty of options. <v Nancy Gibson>Well, it's interesting. You think they're very efficient predators, but actually the only successful five, 10 percent of the time. <v David Heil>Really? Yeah, that's not a very good success rate. So they don't have a lot of range, a lot of animals to hunt. <v Nancy Gibson>Right. That's very true. <v David Heil>That-- in that habitat situation, are they-- are these animals endangered at all in their current habitat? <v Nancy Gibson>There are eight subspecies of tigers. One of them is extinct and the other seven are in dire straits. And they're really having a tough time. Actually, the Bengal tiger is the most numerous, if you call two thousand in the wild, numerous. <v David Heil>OK, so it's not a very good picture right now. Fortunately, Lily's got a home for herself in the zoo and she loves bottled milk. <v Nancy Gibson>Yes, she certainly does. <v David Heil>Nancy, thanks so much for giving us a close look up to what animal that's this rare. <v Nancy Gibson>Good. <v David Heil>That's ll the time we have right now. See you next time on Newton's Apple. <v Speaker 2>Newton's apple is made possible by a grant from Dupont supporting an interest in science today so that future generations may continue to enjoy better things for better living and also by the financial support of yours like you. <v Voiceover Artist>This is PBS.