Science course unit 5

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Description
The programme looks at (l) the states of matter and the forces which bind atoms together (2) Distribution of molecular velocities in a gas and a method for measuring this.

Subtitle Number	Time In	Time Out	Subtitle Text
1	00:00:00,000	00:00:03,000	Gerald Elliott: But first I want you to look at a phenomenon which was…
1	00:00:00,000	00:00:03,000	Alan Walton: But what happens if I increase the kinetic energy?
1	00:00:01,000	00:00:04,000	(Alan Walton) A much more revealing characteristic for study is…
1	00:00:01,000	00:00:03,000	Alan Walton: And you know that if you have a bottle of ammonia say,
2	00:00:03,000	00:00:07,000	..first seen by the botanist Robert Brown looking down his microscope…
2	00:00:04,000	00:00:10,000	Would the solid array perhaps melt? Now I’m not going to try and do this with my fingers.
2	00:00:04,000	00:00:07,000	..the diffusion of one liquid into another.
2	00:00:04,000	00:00:07,000	and take the stopper out, it’s not long before you can…
1	00:00:05,000	00:00:09,000	Alan Walton: I might use these ball bearings to represent atoms.
3	00:00:07,000	00:00:11,000	..at suspensions of pollen grains some hundred years ago.
3	00:00:07,000	00:00:10,000	..smell the ammonia in the other corner of the room.
3	00:00:09,000	00:00:13,000	Here I’m adding some white painted ball bearings to the tray.
4	00:00:10,000	00:00:13,000	Diffusion in gases seems to be a rapid process.
3	00:00:11,000	00:00:14,000	We need a lot of balls and I don’t happen to have enough fingers.
2	00:00:11,000	00:00:15,000	If I did I would still require a repulsive and an attractive force.
4	00:00:12,000	00:00:16,000	He saw that they were constantly in motion, jiggling around in this way, and…
4	00:00:14,000	00:00:16,000	Let’s watch them as they diffuse.
5	00:00:14,000	00:00:18,000	I have a somewhat more controlled experiment here.
4	00:00:15,000	00:00:21,000	So I built myself a sort of tray where I could vibrate a large number of balls at once.
5	00:00:16,000	00:00:19,000	..he asked himself whether this was because there was a living system,
6	00:00:19,000	00:00:22,000	This tube here we pumped out most of the air out of it.
6	00:00:20,000	00:00:25,000	so he did an experiment with suspensions of non-living particles of about the same size,
3	00:00:23,000	00:00:27,000	Well there’s the repulsive force all right – they drive each other apart.
7	00:00:23,000	00:00:28,000	There’s some bromine up here which we can introduce by opening the tap. I'll do it.
7	00:00:25,000	00:00:29,000	gold particles in fact, and convinced himself that it wasn’t a function of…
5	00:00:26,000	00:00:29,000	(Alan Walton) Here’s the tray. It’s been shaken randomly by a motor.
5	00:00:26,000	00:00:29,000	It’s easier to see what’s happening if we use slow motion.
8	00:00:29,000	00:00:31,000	..whether the thing was living or not, he could get…
6	00:00:30,000	00:00:32,000	We’ve given the tray irregular edges as…
4	00:00:30,000	00:00:32,000	Some motor oil.
9	00:00:32,000	00:00:36,000	..just the same molecular motion going on with gold particles.
7	00:00:32,000	00:00:34,000	..we’re trying to simulate things on an atomic scale.
8	00:00:34,000	00:00:36,000	It was certainly a very rapid process.
6	00:00:35,000	00:00:38,000	It’s clearly going to be a lengthy process…
10	00:00:37,000	00:00:40,000	So he said there must be some sorts of forces which were…
8	00:00:38,000	00:00:42,000	If I pour ball bearings onto the stationary tray they will eventually…
5	00:00:38,000	00:00:42,000	And there’s the attractive force – pull one, and the other follows.
9	00:00:38,000	00:00:41,000	It looked as if everything was moving up very rapidly.
7	00:00:39,000	00:00:42,000	..so let’s look at the situation after a period of time has elapsed.
11	00:00:40,000	00:00:44,000	..causing these particles in suspension to jiggle around like this.
10	00:00:41,000	00:00:44,000	Mind you we couldn’t tell the difference between something that was moving up like that,
9	00:00:42,000	00:00:46,000	..crystallise out into the kind of lattice we’ve seen before.
6	00:00:43,000	00:00:46,000	So oily ball bearings represent our atoms.
12	00:00:45,000	00:00:50,000	What then are these forces? To show this I’ve…
8	00:00:45,000	00:00:49,000	The white balls have spread out. A look at any one white bearing and…
11	00:00:45,000	00:00:46,000	and something that was moving up like that.
7	00:00:47,000	00:00:50,000	Now I’ve only used two ball bearings here and in any real system…
12	00:00:47,000	00:00:51,000	There could well be a spread in the speeds of the gas molecules.
8	00:00:50,000	00:00:52,000	..there’s going to be a great many more than two atoms.
9	00:00:50,000	00:00:53,000	..you’ll see that it’s imprisoned in a cell whose walls are its nearest neighbours.