[Script Info]
Title: 
[Events]
Format: Layer, Start, End, Style, Name, MarginL, MarginR, MarginV, Effect, Text
Dialogue: 0,0:00:06.84,0:00:11.67,Default,,0000,0000,0000,,Many of the inanimate objects around you\Nprobably seem perfectly still.
Dialogue: 0,0:00:11.67,0:00:15.66,Default,,0000,0000,0000,,But look deep into the atomic structure\Nof any of them,
Dialogue: 0,0:00:15.66,0:00:18.33,Default,,0000,0000,0000,,and you'll see a world in constant flux.
Dialogue: 0,0:00:18.33,0:00:19.14,Default,,0000,0000,0000,,Stretching,
Dialogue: 0,0:00:19.14,0:00:20.07,Default,,0000,0000,0000,,contracting,
Dialogue: 0,0:00:20.07,0:00:21.00,Default,,0000,0000,0000,,springing,
Dialogue: 0,0:00:21.00,0:00:21.98,Default,,0000,0000,0000,,jittering,
Dialogue: 0,0:00:21.98,0:00:25.16,Default,,0000,0000,0000,,drifting atoms everywhere.
Dialogue: 0,0:00:25.16,0:00:28.36,Default,,0000,0000,0000,,And though that movement may seem chaotic,\Nit's not random.
Dialogue: 0,0:00:28.36,0:00:29.89,Default,,0000,0000,0000,,Atoms that are bonded together,
Dialogue: 0,0:00:29.89,0:00:32.27,Default,,0000,0000,0000,,and that describes almost all substances,
Dialogue: 0,0:00:32.27,0:00:34.88,Default,,0000,0000,0000,,move according to a set of principles.
Dialogue: 0,0:00:34.88,0:00:39.78,Default,,0000,0000,0000,,For example, take molecules,\Natoms held together by covalent bonds.
Dialogue: 0,0:00:39.78,0:00:42.32,Default,,0000,0000,0000,,There are three basic ways \Nmolecules can move:
Dialogue: 0,0:00:42.32,0:00:43.21,Default,,0000,0000,0000,,rotation,
Dialogue: 0,0:00:43.21,0:00:44.34,Default,,0000,0000,0000,,translation,
Dialogue: 0,0:00:44.34,0:00:45.89,Default,,0000,0000,0000,,and vibration.
Dialogue: 0,0:00:45.89,0:00:49.04,Default,,0000,0000,0000,,Rotation and translation \Nmove a molecule in space
Dialogue: 0,0:00:49.04,0:00:52.17,Default,,0000,0000,0000,,while its atoms stay \Nthe same distance apart.
Dialogue: 0,0:00:52.17,0:00:55.61,Default,,0000,0000,0000,,Vibration, on the other hand, \Nchanges those distances,
Dialogue: 0,0:00:55.61,0:00:58.25,Default,,0000,0000,0000,,actually altering the molecule's shape.
Dialogue: 0,0:00:58.25,0:01:02.69,Default,,0000,0000,0000,,For any molecule, you can count up\Nthe number of different ways it can move.
Dialogue: 0,0:01:02.69,0:01:05.30,Default,,0000,0000,0000,,That corresponds to \Nits degrees of freedom,
Dialogue: 0,0:01:05.30,0:01:06.94,Default,,0000,0000,0000,,which in the context of mechanics
Dialogue: 0,0:01:06.94,0:01:10.45,Default,,0000,0000,0000,,basically means the number of variables\Nwe need to take into account
Dialogue: 0,0:01:10.45,0:01:13.34,Default,,0000,0000,0000,,to understand the full system.
Dialogue: 0,0:01:13.34,0:01:18.02,Default,,0000,0000,0000,,Three-dimensional space is defined by\Nx, y, and z axes.
Dialogue: 0,0:01:18.02,0:01:23.03,Default,,0000,0000,0000,,Translation allows the molecule to move\Nin the direction of any of them.
Dialogue: 0,0:01:23.03,0:01:25.10,Default,,0000,0000,0000,,That's three degrees of freedom.
Dialogue: 0,0:01:25.10,0:01:28.76,Default,,0000,0000,0000,,It can also rotate around \Nany of these three axes.
Dialogue: 0,0:01:28.76,0:01:29.99,Default,,0000,0000,0000,,That's three more,
Dialogue: 0,0:01:29.99,0:01:33.04,Default,,0000,0000,0000,,unless it's a linear molecule, \Nlike carbon dioxide.
Dialogue: 0,0:01:33.04,0:01:37.46,Default,,0000,0000,0000,,There, one of the rotations just spins\Nthe molecule around its own axis,
Dialogue: 0,0:01:37.46,0:01:41.61,Default,,0000,0000,0000,,which doesn't count because it doesn't\Nchange the position of the atoms.
Dialogue: 0,0:01:41.61,0:01:44.60,Default,,0000,0000,0000,,Vibration is where it gets a bit tricky.
Dialogue: 0,0:01:44.60,0:01:46.98,Default,,0000,0000,0000,,Let's take a simple molecule,\Nlike hydrogen.
Dialogue: 0,0:01:46.98,0:01:51.68,Default,,0000,0000,0000,,The length of the bond the holds the two\Natoms together is constantly changing
Dialogue: 0,0:01:51.68,0:01:54.48,Default,,0000,0000,0000,,as if the atoms were connected \Nby a spring.
Dialogue: 0,0:01:54.48,0:01:58.98,Default,,0000,0000,0000,,That change in distance is tiny,\Nless than a billionth of a meter.
Dialogue: 0,0:01:58.98,0:02:03.79,Default,,0000,0000,0000,,The more atoms and bonds a molecule has,\Nthe more vibrational modes.
Dialogue: 0,0:02:03.79,0:02:06.82,Default,,0000,0000,0000,,For example, a water molecule \Nhas three atoms:
Dialogue: 0,0:02:06.82,0:02:10.16,Default,,0000,0000,0000,,one oxygen and two hydrogens,\Nand two bonds.
Dialogue: 0,0:02:10.16,0:02:12.48,Default,,0000,0000,0000,,That gives it three modes of vibration:
Dialogue: 0,0:02:12.48,0:02:13.82,Default,,0000,0000,0000,,symmetric stretching,
Dialogue: 0,0:02:13.82,0:02:15.41,Default,,0000,0000,0000,,asymmetric stretching,
Dialogue: 0,0:02:15.41,0:02:16.90,Default,,0000,0000,0000,,and bending.
Dialogue: 0,0:02:16.90,0:02:21.14,Default,,0000,0000,0000,,More complicated molecules have even\Nfancier vibrational modes,
Dialogue: 0,0:02:21.14,0:02:22.43,Default,,0000,0000,0000,,like rocking,
Dialogue: 0,0:02:22.43,0:02:23.61,Default,,0000,0000,0000,,wagging,
Dialogue: 0,0:02:23.61,0:02:25.20,Default,,0000,0000,0000,,and twisting.
Dialogue: 0,0:02:25.20,0:02:29.85,Default,,0000,0000,0000,,If you know how many atoms a molecule has,\Nyou can count its vibrational modes.
Dialogue: 0,0:02:29.85,0:02:32.01,Default,,0000,0000,0000,,Start with the total degrees of freedom,
Dialogue: 0,0:02:32.01,0:02:35.43,Default,,0000,0000,0000,,which is three times the number\Nof atoms in the molecule.
Dialogue: 0,0:02:35.43,0:02:38.84,Default,,0000,0000,0000,,That's because each atom can move\Nin three different directions.
Dialogue: 0,0:02:38.84,0:02:41.39,Default,,0000,0000,0000,,Three of the total correspond \Nto translation
Dialogue: 0,0:02:41.39,0:02:44.63,Default,,0000,0000,0000,,when all the atoms \Nare going in the same direction.
Dialogue: 0,0:02:44.63,0:02:49.43,Default,,0000,0000,0000,,And three, or two for linear molecules,\Ncorrespond to rotations.
Dialogue: 0,0:02:49.43,0:02:53.100,Default,,0000,0000,0000,,All the rest, 3N-6\Nor 3N-5 for linear molecules,
Dialogue: 0,0:02:53.100,0:02:56.13,Default,,0000,0000,0000,,are vibrations.
Dialogue: 0,0:02:56.13,0:02:57.96,Default,,0000,0000,0000,,So what's causing all this motion?
Dialogue: 0,0:02:57.96,0:03:02.05,Default,,0000,0000,0000,,Molecules move because they absorb\Nenergy from their surroundings,
Dialogue: 0,0:03:02.05,0:03:05.75,Default,,0000,0000,0000,,mainly in the form of heat\Nor electromagnetic radiation.
Dialogue: 0,0:03:05.75,0:03:08.36,Default,,0000,0000,0000,,When this energy gets transferred\Nto the molecules,
Dialogue: 0,0:03:08.36,0:03:09.42,Default,,0000,0000,0000,,they vibrate,
Dialogue: 0,0:03:09.42,0:03:10.22,Default,,0000,0000,0000,,rotate,
Dialogue: 0,0:03:10.22,0:03:12.51,Default,,0000,0000,0000,,or translate faster.
Dialogue: 0,0:03:12.51,0:03:16.53,Default,,0000,0000,0000,,Faster motion increases the kinetic energy\Nof the molecules and atoms.
Dialogue: 0,0:03:16.53,0:03:20.79,Default,,0000,0000,0000,,We define this as an increase \Nin temperature and thermal energy.
Dialogue: 0,0:03:20.79,0:03:25.44,Default,,0000,0000,0000,,This is the phenomenon your microwave oven\Nuses to heat your food.
Dialogue: 0,0:03:25.44,0:03:29.25,Default,,0000,0000,0000,,The oven emits microwave radiation,\Nwhich is absorbed by the molecules,
Dialogue: 0,0:03:29.25,0:03:31.72,Default,,0000,0000,0000,,especially those of water.
Dialogue: 0,0:03:31.72,0:03:33.66,Default,,0000,0000,0000,,They move around faster and faster,
Dialogue: 0,0:03:33.66,0:03:38.10,Default,,0000,0000,0000,,bumping into each other and increasing\Nthe food's temperature and thermal energy.
Dialogue: 0,0:03:38.10,0:03:40.51,Default,,0000,0000,0000,,The greenhouse effect is another example.
Dialogue: 0,0:03:40.51,0:03:43.25,Default,,0000,0000,0000,,Some of the solar radiation \Nthat hits the Earth's surface
Dialogue: 0,0:03:43.25,0:03:45.60,Default,,0000,0000,0000,,is reflected back to the atmosphere.
Dialogue: 0,0:03:45.60,0:03:51.01,Default,,0000,0000,0000,,Greenhouse gases, like water vapor\Nand carbon dioxide absorb this radiation
Dialogue: 0,0:03:51.01,0:03:52.49,Default,,0000,0000,0000,,and speed up.
Dialogue: 0,0:03:52.49,0:03:57.57,Default,,0000,0000,0000,,These hotter, faster-moving molecules\Nemit infrared radiation in all directions,
Dialogue: 0,0:03:57.57,0:04:00.35,Default,,0000,0000,0000,,including back to Earth, warming it.
Dialogue: 0,0:04:00.35,0:04:03.34,Default,,0000,0000,0000,,Does all this molecular motion ever stop?
Dialogue: 0,0:04:03.34,0:04:05.94,Default,,0000,0000,0000,,You might think that would happen\Nat absolute zero,
Dialogue: 0,0:04:05.94,0:04:07.82,Default,,0000,0000,0000,,the coldest possible temperature.
Dialogue: 0,0:04:07.82,0:04:10.68,Default,,0000,0000,0000,,No one's ever managed to cool\Nanything down that much,
Dialogue: 0,0:04:10.68,0:04:11.100,Default,,0000,0000,0000,,but even if we could,
Dialogue: 0,0:04:11.100,0:04:16.21,Default,,0000,0000,0000,,molecules would still move due to\Na quantum mechanical principle
Dialogue: 0,0:04:16.21,0:04:18.56,Default,,0000,0000,0000,,called zero-point energy.
Dialogue: 0,0:04:18.56,0:04:22.75,Default,,0000,0000,0000,,In other words, everything has been moving\Nsince the universe's very first moments,
Dialogue: 0,0:04:22.75,0:04:26.22,Default,,0000,0000,0000,,and will keep going long, \Nlong after we're gone.