DIY Podcast: Newton's Laws Audio Clips Transcript
International Space Station Expedition 16 Flight Engineer Dan Tani discusses Newton's laws. You can mix these audio clips with your own narration. Listen to the audio and download the clips you want to use in your podcast or other audio production.

Dan Tani: 1-a. Things at rest stay at rest. And things in motion stay in motion in a straight line unless there's some sort of force imposed on it like a wall or gravity or your hand or anything. OK. Second law is F=ma. Very simple equation, but really, really complex when you start to think about it. And maybe you'll work with F=ma in your class. And the third is for every action there is an equal and opposite reaction. And think of that every time any kind of force is applied to you, when you're walking or maybe when you hit a baseball -- the motion imposed on the ball, there's an equal force imposed on the bat, also -- or something like that. So, that Sir Isaac Newton, he was a pretty smart guy. And if you just learn the three laws of motion that he came up with, I think you'll go a long way in understanding how things move, and maybe you'll get really excited about science because it really is fun.

2-a. Now, Sir Isaac Newton was a pretty smart guy. And before he came around people had different ideas of how things moved and why things moved.

3-a. A lot of people thought that matter -- things -- always wanted to stay at rest because they noticed when they dropped things, they would fall to the floor and eventually they would stop moving. Or if (people) threw a ball: They would throw it; it would roll; but it would eventually stop. So people thought back then that stuff -- things, matter -- always wanted to stop. It didn't want to move. You had to force it to move, but eventually it would stop.

4-a. Sir Isaac thought differently, and he came up with three laws of motion that really made understanding how motion works completely revolutionary and completely new. And they call them rules -- laws, the three laws of motion.

5-a. First law says things at rest stay at rest and things in motion stay in motion unless those things have a force imposed on them.

6-a. Let's pretend like I'm on the ground in your classroom. And if I were to take one of these candy-coated chocolates and let go of it, what would happen? Well, it would go crashing onto the ground, wouldn't it? And then when I ate it, it would have to be a dirty chocolate that fell on the ground.

7-a. The reason that happens to you in your classroom or on the ground is there's a force exerted on the chocolate, and that force is provided by gravity. OK. And that force is always straight down. So, if you were to drop the candy-coated chocolate, it would fall to the ground because it has a force imposed on it.

8-a. But here in the space station and in low Earth orbit we are under microgravity, which is essentially no gravity -- no apparent gravity. So, if I let go of the candy, it doesn't fall. It stays at rest because there's no external force on it. OK. Actually, there's a little force because we have fans going and so the force is provided by the airflow, but basically there's no force on it until an external force is imposed on it.

9-a. If I were to throw this, OK, or toss it a little bit, and we were on the ground, well, it would slowly go back down to the ground and hit the floor. And the floor would impose its force on it and stop the motion of the candy. But here in space, it just keeps going in a straight line.

10-a. Newton's second law says that force is equal to the mass of the object times the acceleration imposed on it. OK. F=ma. You might have heard that.

11-a. F=ma. That's a pretty simple equation, but it really means a whole lot to people who study how things move. Let's do a little demonstration of F=ma. I'm down here on the floor of the space station -- or we call it "the deck" -- because we have some bungees set up. Bungees hold our stuff down. But a bungee's a good way to impose a particular amount of force on things because it's elastic, and you pull it back a little bit and you let go and it has some force. So, we can apply approximately the same amount of force to different things.

12-a. Candy has just a little bit of mass. Now, mass, we think of it like weight, but that's because on Earth we're under the same acceleration everywhere -- the acceleration of gravity. OK. So the weight equals the mass of this, or mass of anything, times acceleration, which is gravity. So that's why something that has a lot of mass like a watermelon feels heavier, or is heavier, on the Earth than a candy-coated chocolate because a watermelon has more mass than candy.

13-a. The force that the bungee exerted equaled the mass, which is small, times the acceleration that it experienced. So, big acceleration. Little mass. For the same amount of force. OK. So, force just equals ma.

14-a. Newton's third law of motion says that for every action there's an equal but opposite reaction.

15-a. For all of you that are sitting in your chairs, you are putting a force -- your weight -- on the chair. OK. But we always said that things in motion stay in motion. And you have a force -- that's your weight -- going down on the Earth. So how come you're not moving? Well, because there's an equal force that the chair is imposing on you so that you are just sitting in your chair, and then there's a force that the floor is imparting on you and the chair. So where the chair meets the floor, there's the weight of you and the chair. And then there's an equal force that the Earth places upon the chair so that you don't move, OK, because the forces have to equal out.

16-a. I pushed away the water. I lifted my feet so I was floating. And it went away with the speed and I went away with the speed because when I pushed, that action had an equal and opposite reaction on me. So the force that we pushed the water off, I used the same force to push myself back. OK. But I went slower because I have more mass than the water.

17-a. When you get a little bit deeper into the equations of motion, you can figure out that if the bag weighed one third of what I weigh -- I guess that's about right -- then I probably moved away with one third less velocity than the bag did. The bag probably had three times the velocity that I did. But that's probably in a little bit more advanced physics than the simple three laws of motion.

18-a. And this is how rockets work. What rockets do is they throw out their propellant. Propellant is really heavy, and, like when the shuttle is on the launch pad, the shuttle and its rockets weigh about four and a half million pounds. But the shuttle itself only weighs about a quarter of a million pounds. OK, so what is that? Many times -- four, 16, 20 -- about 20 times more propellant than there is shuttle. So all that mass gets used to propel the shuttle into orbit. And what it does is the rocket engines create combustion, and it spits out the mass of that propellant out the back of those engines, and that mass, that force, pushes the shuttle into space. And that's how rockets work.


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