1
00:00:08,206 --> 00:00:10,438
Energy is not easy to define.

2
00:00:10,438 --> 00:00:12,053
Things have energy,

3
00:00:12,053 --> 00:00:12,960
but you can't hold

4
00:00:12,960 --> 00:00:14,822
a bushel of energy in your hands.

5
00:00:14,822 --> 00:00:16,483
You can see what it does,

6
00:00:16,483 --> 00:00:18,804
but you can't see it directly.

7
00:00:18,804 --> 00:00:20,615
There are different types of energy,

8
00:00:20,615 --> 00:00:21,916
but the differences between them

9
00:00:21,916 --> 00:00:25,692
are manifested only in how they make stuff behave.

10
00:00:25,692 --> 00:00:27,045
We do know that the total amount

11
00:00:27,045 --> 00:00:29,165
of all the different types of energy in the universe

12
00:00:29,165 --> 00:00:31,366
is always the same.

13
00:00:31,366 --> 00:00:33,546
And, for chemists, two important types of energy

14
00:00:33,546 --> 00:00:35,107
are chemical potential energy

15
00:00:35,107 --> 00:00:36,886
and kinetic energy.

16
00:00:36,886 --> 00:00:39,721
Potential energy is energy waiting to happen.

17
00:00:39,721 --> 00:00:41,801
Think of a stretched rubber band.

18
00:00:41,801 --> 00:00:42,629
If you cut it,

19
00:00:42,629 --> 00:00:44,008
all that potential energy

20
00:00:44,008 --> 00:00:46,743
gets converted to kinetic energy,

21
00:00:46,743 --> 00:00:49,599
which is registered by you as pain.

22
00:00:49,599 --> 00:00:50,850
Like a stretched rubber band,

23
00:00:50,850 --> 00:00:52,848
chemical bonds also store energy,

24
00:00:52,848 --> 00:00:54,102
and when those bonds are broken,

25
00:00:54,102 --> 00:00:55,603
that potential energy gets converted

26
00:00:55,603 --> 00:00:57,116
to other types of energy,

27
00:00:57,116 --> 00:00:58,435
like heat or light,

28
00:00:58,435 --> 00:01:00,850
or gets used to make different bonds.

29
00:01:00,850 --> 00:01:03,497
Kinetic energy is the energy of motion,

30
00:01:03,497 --> 00:01:05,623
and molecules are always moving.

31
00:01:05,623 --> 00:01:07,614
They're not necessarily going somewhere,

32
00:01:07,614 --> 00:01:08,939
though they could be,

33
00:01:08,939 --> 00:01:10,015
but they are vibrating,

34
00:01:10,015 --> 00:01:10,517
stretching,

35
00:01:10,517 --> 00:01:10,932
bending,

36
00:01:10,932 --> 00:01:12,372
and/or spinning.

37
00:01:12,372 --> 00:01:13,122
Take methane,

38
00:01:13,122 --> 00:01:14,269
which is four hydrogens

39
00:01:14,269 --> 00:01:15,678
attached to a central carbon,

40
00:01:15,678 --> 00:01:16,624
as an example.

41
00:01:16,624 --> 00:01:17,501
Drawn on paper,

42
00:01:17,501 --> 00:01:19,799
it's just a still tetrahedron.

43
00:01:19,799 --> 00:01:22,467
But in real life, it's a jiggling mess.

44
00:01:22,467 --> 00:01:23,807
The kinetic energy of molecules

45
00:01:23,807 --> 00:01:25,720
is exactly the same type of energy

46
00:01:25,720 --> 00:01:27,120
as the energy you have

47
00:01:27,120 --> 00:01:28,434
when you're moving around,

48
00:01:28,434 --> 00:01:30,058
except that you can be still

49
00:01:30,058 --> 00:01:31,820
and molecules can't.

50
00:01:31,820 --> 00:01:33,315
If you suck the kinetic energy

51
00:01:33,315 --> 00:01:34,512
out of a group of molecules,

52
00:01:34,512 --> 00:01:35,770
they'll move less,

53
00:01:35,770 --> 00:01:37,266
but they'll never fully stop.

54
00:01:37,266 --> 00:01:39,017
Now, in any group of molecules,

55
00:01:39,017 --> 00:01:41,854
some will have more kinetic energy than others.

56
00:01:41,854 --> 00:01:42,555
And if we calculate

57
00:01:42,555 --> 00:01:44,520
the average kinetic energy of the group,

58
00:01:44,520 --> 00:01:47,334
we'd have a number mathematically related to

59
00:01:47,334 --> 00:01:48,659
temperature.

60
00:01:48,659 --> 00:01:50,069
So, the more kinetic energy

61
00:01:50,069 --> 00:01:51,376
a group of molecules has,

62
00:01:51,376 --> 00:01:52,876
the higher its temperature.

63
00:01:52,876 --> 00:01:54,562
And that means that on a hot day,

64
00:01:54,562 --> 00:01:56,231
the molecules in the air around you

65
00:01:56,231 --> 00:01:58,017
are spinning, stretching, bending,

66
00:01:58,017 --> 00:02:00,196
and generally shooting around much faster

67
00:02:00,196 --> 00:02:02,322
than on a cold day.

68
00:02:02,322 --> 00:02:04,275
Now, hot and cold, by the way,

69
00:02:04,275 --> 00:02:05,645
are relative terms.

70
00:02:05,645 --> 00:02:07,141
They're always used to compare

71
00:02:07,141 --> 00:02:08,649
one thing to something else.

72
00:02:08,649 --> 00:02:09,869
So, on that hot summer day,

73
00:02:09,869 --> 00:02:11,814
the air molecules have more kinetic energy

74
00:02:11,814 --> 00:02:14,604
than the molecules in your skin.

75
00:02:14,604 --> 00:02:16,979
So, when those air molecules crash into you,

76
00:02:16,979 --> 00:02:18,741
they transfer some of their energy

77
00:02:18,741 --> 00:02:20,493
to the molecules in your skin,

78
00:02:20,493 --> 00:02:22,811
and you feel that as heat.

79
00:02:22,811 --> 00:02:23,581
On a cold day,

80
00:02:23,581 --> 00:02:25,757
the air molecules have less kinetic energy

81
00:02:25,757 --> 00:02:27,108
than the molecules in your skin,

82
00:02:27,108 --> 00:02:29,481
so when you crash into those air molecules,

83
00:02:29,481 --> 00:02:30,726
you actually transfer

84
00:02:30,726 --> 00:02:33,232
some of your kinetic energy to them,

85
00:02:33,232 --> 00:02:35,973
and you feel that as cold.

86
00:02:35,973 --> 00:02:38,597
You can trace the path of energy around you.

87
00:02:38,597 --> 00:02:40,243
Try it at your next cookout.

88
00:02:40,243 --> 00:02:41,148
You burn charcoal

89
00:02:41,148 --> 00:02:43,145
and the release of that chemical potential energy

90
00:02:43,145 --> 00:02:45,725
shows up as extreme heat and light.

91
00:02:45,725 --> 00:02:47,273
The heat then makes the molecules

92
00:02:47,273 --> 00:02:50,056
of your burgers, your hot dogs, or your vegetables

93
00:02:50,056 --> 00:02:52,309
vibrate until their own bonds break

94
00:02:52,309 --> 00:02:54,649
and new chemical structures are formed.

95
00:02:54,649 --> 00:02:56,646
Too much heat and you have a charred mess;

96
00:02:56,646 --> 00:02:58,330
just enough and you have dinner.

97
00:02:58,330 --> 00:02:59,454
Once in your body,

98
00:02:59,454 --> 00:03:01,075
the food molecules in your delicious,

99
00:03:01,075 --> 00:03:02,297
or charred,

100
00:03:02,297 --> 00:03:03,829
dinner get broken down,

101
00:03:03,829 --> 00:03:04,816
and the energy released

102
00:03:04,816 --> 00:03:07,346
is used to either keep you alive right now

103
00:03:07,346 --> 00:03:10,339
or it's stored for later in different molecules.

104
00:03:10,339 --> 00:03:11,752
As night falls,

105
00:03:11,752 --> 00:03:13,217
the hot summer air cools

106
00:03:13,217 --> 00:03:15,855
and the flow of energy into you slows.

107
00:03:15,855 --> 00:03:18,551
Then, as the air reaches your skin temperature,

108
00:03:18,551 --> 00:03:19,812
for the briefest of moments,

109
00:03:19,812 --> 00:03:21,141
the flow stops.

110
00:03:21,141 --> 00:03:22,395
And then it starts up again

111
00:03:22,395 --> 00:03:23,640
in the opposite direction

112
00:03:23,640 --> 00:03:26,358
as energy leaves the warmer surface of your skin

113
00:03:26,358 --> 00:03:29,058
to return to the universe around you,

114
00:03:29,058 --> 00:03:31,726
that energy, neither created nor destroyed,

115
00:03:31,726 --> 00:03:33,620
but ever shape-shifting,

116
00:03:33,620 --> 00:03:36,230
the chameleon phoenix of our physical world.