Fun to Imagine Richard P. Feynman BBC 1983 transcript by A. Wojdyla This is a transcript of the R.P. Feynman s Fun to imagine aired on BBC in 1983. The transcript was made by a non-native english speaker (perdon my French!), so there might be some blanks (**) that were reproduced here. On overall, it should be fine though. I ve also try to keep close to the very idiomatic language of the speaker. Grammar mistakes are actually his! A translation to French is available here : http://antoine.wojdyla.free.fr/feynman_fun_fr.html It's Interesting that some people find science so easy and others find it kind of dull and difficult especially kids; you know, some of them are just heated up, and I don't know why it is. It's the same for all... (**) For instance some people love music and I could never carry a tune. I lose a great deal a pleasure out of that and I think that people lose a lot of pleasure who find the science dull. In the case of science, I think that one of the things that make it difficult is that it takes a lot of imagination. It's very hard to imagine all the crazy things that things really are like. Jiggling atoms Nothing is really as it seems used to be (**) The hot is the speed at the atoms are jiggling; if they jiggle more, it corresponds to the
hotter, and colder is jiggling less. So if you have a bunch of atom, like a cup of coffee or something, sitting on a table, and the atoms are jiggling a great deal and they bounce against the cup, and the cup gets shaking, and the atoms in the cup shakes, and the bounce against each other, so the heat heats the cup. Hot things spread that heat to other by mere contact, because the atoms are jiggling a lot in a hot thing shake the ones that are jiggling only a little bit in the cold thing so the hot (heat we say) goes into the cold thing, it spreads; but what is spreading is just jiggling, an irregular motion, but it is easy to understand. It brings up another thing that's kind of curious: that the -- when I say that things jiggle (**) like the ball bounces, you know they slow up and stop after a while. But we have to imagine with the atom prefect elasticity, they never lose any energy; anytime they bounce they keep on bouncing, they don't lose anything, and they re perpetually moving. And that the things that happen when we say something loses energy, like the ball coming down and bouncing, it shakes irregularly some of the atoms in the floor, and when it comes up again, it leaves some of the atoms moving, jiggling. So as it bounces, it is passing its extra energy, its extra motion, to little patches on the floor each time it rebounces and it loses a little heat each time, until it settles down, we say as the falling motion stops. But what's left is the floor is shaking more than it was before, and the atoms in the ball are shaking more than they were before, that the organized motion of all these atoms moving the same way falling down, and the quiet floor, is now transformed into a ball sitting on the ground. All the motion is still there in the form of energy of motion, in the form of the jiggling of the floor which is a little bit warmer (unbelievable!). But anybody who has hammered a great deal of something knows that it's true, that if
you (pound**) something a lot, you can feel the temperature difference: it heats up. It heats up simply because you are jiggling it. This picture -atoms- is a beautiful one if you keep looking all kind of things this way. In a little drop of water -a tiny drop-, the atoms attracts each other; they like to be next to each other, they want to have as many partners as they can get. Now the guy at the surface has only partners on one side, it has air on the other side; he tries to get in. And you can imagine this of people, this team in people, all of them moving very fast, all try to get -have- as many partners as possible; the guys on the edge are very unhappy and nervous and they keep pounding in, trying to get in, and that makes a tight ball instead of a flat. That's surface tension, you realize when you see sometimes that a water drop sits like this on a table, and then you start to imagine why it's like that -because everybody is trying to get in to the water. And -- At the same time while all this is happening, other atoms leaving the surface, and the water drop is slowly disappearing. I find myself trying to imagine all the kind of things all the time, and I get a kick out of it like a runner gets a kick out of sweating. I GET A KICK of thinking about these things! I can't stop. I can talk forever! If you could cool off the water so that the jiggling is less and less, it jiggles slower and slower, then the atoms get stuck in a place, they like to be with their friend; there's force of attraction and they get packed together, they're not rolling over each other, they're in a nice pattern, like oranges in a cradle(**), in a nice, organized patch(**). All of them are jiggling in place, but not having enough motion to get loose of their own place and to break the structure down. And that what I'm describing is a solid - ice-, it has a structure. If you held the atom in one end in a certain position, all the rest
are lining up in a position sticking out, and it s solid at the end. Whereas if you heat that harder, then they begin to get loose and roll all over each other, and that's the liquid. And if you heat that still harder, then they bounce still harder, and they simply bounce apart from each other and they're just individuals, isolated atoms - I said atoms, these are really little groups of atoms: molecule- which come flying and hit and all over they have (**) the tendency to (**), they're moving too fast, their hands don't grab so to speak, and they fly up again, and this is the gas called steam. You can get all kinds of understanding. When I was a kid with this "air", I was always interesting. I've noticed that when I pumped up my tires on the bicycle (you can learn a lot by having a bicycle). It pumps up the tire and the pump will get hot, and I also understand that as the pump handle comes down and the atoms are coming up against it and bounce, and it's moving in (**), the ones that are coming off have a bigger speed than the ones that are coming in, so that as it comes down, each time they collide, it speeds them up, and so they're hotter when you compress the gas it heats. And when you pull the piston back out, then the atoms that are coming faster than the piston feel a sort of seeding, give (**) and come out with les energy. It's like going against something that is so after (**) boomp boomp and it loses. So as you pull the piston out, and the atoms are hit, they lose their speed and they cool off. Then he gas gets cool as it expands. And the fun of it is that all these things, which you certainly noticed in the world about it : the pump, heats the gas, whether the gas cools when it expands(**), whether the steam evaporates until you cover the cover, and all these things you can understand from this simple picture. And that's a kind of lot of fun to think. I don't want to take this stuff seriously;i think we should just have fun imagining it, not worry about. There is no teaching when you are asking a question at the end, otherwise it's a horrible subject.
Rubber bands Most elastic things like steel springs and so on are nothing but these electrical things pulling back and pulling atoms a little bit apart when you bend something, and then they try to come back together again. But rubber bands work on a different principle: there are some long molecules like chains. And other little ones that are shaking all the time (*bump on the other little chains). And the chains are all kind of kinky (*). When you pull up the rubber band, the string gets straighter. But these strings are being bombarded on the side by these other atoms trying to shorten them, by kicking them. So it pulls back (it's trying to pull back), and this pulling back is only because of the heat. So if you hit a rubber band, it will pull more strongly. For instance, if you hang a weight on the rubber band with a little mass, it is kind of fun to watch it rise (*), and there's another thing you could check this idea is right (that it's heat that drives the rubber band): if you pull the band out, just like you push the piston on the gas, if you pull the band out, these tightening string hitting the moleculesmakes them move faster, and so it is warmer. And if you take the band and let it in, then the molecules hitting the strings which sort of give as the thing heats, they give in to the the(*), and they lose energy when they hit this retiring band, straight string. So it cools. And there is a little way you could do this (you're not very sensitive; it's a small effect). If you take a fairly wide rubber band, and put it between your lips, and pull it out, you'll certainly notice it's hotter. And then if you then hold it out and let in, you will notice that it is cooler; at least you will notice there's a certain difference in what happens when you expand it and when you contract it. And (*Ivory's) found rubber band fascinating to think. When they're sitting on an old package of paper for a lonnnnnng time, holding those papers together, it is done by a perpetual pounding
pounding pounding, and these atoms that gets these chains to hold it, trying to keep them and keep them, year after year (well, rubber bands don't last that long, but, heyy... a long time), trying to hold this whole thing together. The world is a dynamic mess of giggling things if you look at it right. And if you magnify, you will hardly see a little thing anymore, because everything is jiggling in its own pattern, and there's a lot of little balls. It's lucky that we have such a large scale of view of everything, that we can see these as things, without having worry about all these little atoms all the time. Fire The atoms like each other to different degrees. Oxygen, for instance in the air, would like to be next to carbon, and if they get near they snap each other. If they're not too close though, they repel and they go apart, so they don't that they could snap together. It's just as if you have a bowl (**) and are trying to climb a hall where there' a hole you can go into -the volcano hole- a deep one, it's rolling along and doesn't go down in the deep hole because it starts to climb the hill and goes away again. But if you make it go fast enough, it'll fall into the hole. And so, if you take something like wood and oxygen; there's carbon in the wood from the tree, and the oxygen comes and hits the carbon, but not hard enough; it just goes away again -the air is like nothing. If you can get it faster, by heating it up sometimes, somewhere, somehow, get it started, a few a them comes fast, they go over the top surface, they come closer to the carbon and then snap in, and that keeps a lot of jiggling motion (**), which might hit some other again, making those go fast, so they can climb up and bump against other carbon atoms, and jiggle and they make other jiggle, and you get an horrible
catastrophe, where all one after the other are going faster and faster and snapping in and the whole thing is changing. That catastrophe is a fire. It's just a way of looking at it, and these are happening, it is perpetual, once the thing gets started, it keeps going, the heat makes other atoms capable of reaching, to make more heat, to make other atom... and so on! So this terrible snapping is producing a lot a jiggling, and if I put all that activity of the atoms, I could put a cup of coffee over that (**). Messy wood! That's giving a lot of jiggling. That's what the heat of the fire is. And then of course, you see what's happening when you start it, it goes on and on(**). When it get started, why is that the wood has been surviving all this time with the oxygen all this time, and it didn't do it earlier or something? Where did I get this from? Why did it came (**) from the tree. And the substance of the tree is carbon, and where does it come from? That comes from the air, it's carbon dioxide from the air. People cut trees and think that it comes from the ground. The plant grows out from the ground. But if you asked "where the substance come from?", you find out where does it come from (**) the tree is coming out of the air? They surely come out of the ground! No, they come out of the air! The carbon dioxide in the air goes into the tree, and changes it, kicking out the oxygen, and pushing the oxygen away from the carbon, and leaving the carbon substance (topped) with water. Water comes out of the ground, you see; only is that it has to get there out of the (**) air, it came down from the sky. So in fact most of the tree is out of the ground -I'm sorry: it's out of the air! There's a little bit from the ground: some minerals and so forth. Now, of course I told you that the we know oxygen and carbon sticks together tight (**) How is that the tree is so smart to take the carbon dioxide (which is carbon and oxygen nicely combined), and undo that so easy?
Ah! Life! Life has some mysterious ways! No! The sun is shining, and this sunlight comes down and knocks this oxygen away from the carbon, so it takes some light to get the plant to work! And so the sun, all the time, is doing the work of separating the oxygen away from the carbon, the oxygen is sort a of terrible by-product, which it spits back into the air, an leave in the carbon and water to make the substance of the tree. And then we take the substance of the tree to get the fireplace. All the oxygen made by these trees and all the carbons would much prefer to be together again. And once you let the heat to get it started, it continues and make an awful lot of activity while it's going back together again, and all those nice light and everything comes out, and everything is being undone, you're going from carbon and oxygen back to carbon dioxide, and the light and heat that's coming out is the light and heat of the sun that went in, so it's sort of stored sun that is coming out when you burn it. Now the next question: how is the sun so jiggly, so hot? I gotta stop somewhere; I leave you something to imagine