1
00:00:15,966 --> 00:00:16,900
And why this matters.

2
00:00:16,900 --> 00:00:19,602
Because in fact, this
is one of the things,

3
00:00:19,602 --> 00:00:22,939
all the way back to Hook
and his cannonballs,

4
00:00:22,939 --> 00:00:26,776
and even way before that,
people noticed this stuff.

5
00:00:26,776 --> 00:00:29,346
I broke something,
but it always seems

6
00:00:29,346 --> 00:00:31,915
to slice in a certain way.

7
00:00:31,915 --> 00:00:32,515
Why is that?

8
00:00:32,515 --> 00:00:36,553
Why would something always break
in the same way every time?

9
00:00:36,553 --> 00:00:38,388
With the same kind of--

10
00:00:38,388 --> 00:00:40,056
what does way mean here?

11
00:00:40,056 --> 00:00:42,125
It means like the
angles that form.

12
00:00:42,125 --> 00:00:45,996
So why are those angles
always kind of the same?

13
00:00:45,996 --> 00:00:48,198
Well, it has to do
with the strength,

14
00:00:48,198 --> 00:00:51,034
the relative strength,
of the planes

15
00:00:51,034 --> 00:00:53,570
inside of these crystals.

16
00:00:53,570 --> 00:00:55,939
And in fact, here's
a beautiful piece

17
00:00:55,939 --> 00:00:58,108
of work on stretching a wire.

18
00:00:58,108 --> 00:01:02,312
All right, so here you're taking
a wire that is crystalline

19
00:01:02,312 --> 00:01:03,813
and you're pulling it.

20
00:01:03,813 --> 00:01:05,682
And you can see how it breaks.

21
00:01:05,682 --> 00:01:07,350
You can actually
see how it breaks.

22
00:01:07,350 --> 00:01:10,387
It's breaking along
the weakest plane.

23
00:01:10,387 --> 00:01:11,988
It's breaking along
the weakest plane.

24
00:01:11,988 --> 00:01:14,289
So if you want to think,
then, about well, OK,

25
00:01:14,289 --> 00:01:18,027
how do I know how to make
this stronger, for example?

26
00:01:18,027 --> 00:01:20,096
So it stops breaking--
you know, the weakest link

27
00:01:20,096 --> 00:01:22,399
is the weakest link.

28
00:01:22,399 --> 00:01:22,999
That was deep.

29
00:01:26,703 --> 00:01:28,670
So then that's the
plane of the crystal

30
00:01:28,670 --> 00:01:29,806
that I need to think about.

31
00:01:29,806 --> 00:01:34,811
How are bonding together or
packing in in that plane?

32
00:01:34,811 --> 00:01:35,878
This is real stuff.

33
00:01:35,878 --> 00:01:39,582
This comes about in many
of the properties, not just

34
00:01:39,582 --> 00:01:44,888
the fracture, but in many of the
properties of these materials.

35
00:01:44,888 --> 00:01:49,225
The property, as I said before,
depends heavily on which plane

36
00:01:49,225 --> 00:01:50,060
you're in.

37
00:01:50,060 --> 00:01:52,529
And we'll see that
more and more.