[Script Info]
Title: 
[Events]
Format: Layer, Start, End, Style, Name, MarginL, MarginR, MarginV, Effect, Text
Dialogue: 0,0:00:07.02,0:00:09.96,Default,,0000,0000,0000,,Sitting around a campfire, \Nyou can feel its heat,
Dialogue: 0,0:00:09.96,0:00:13.17,Default,,0000,0000,0000,,smell the woody smoke, \Nand hear it crackle.
Dialogue: 0,0:00:13.17,0:00:14.44,Default,,0000,0000,0000,,If you get too close,
Dialogue: 0,0:00:14.44,0:00:17.11,Default,,0000,0000,0000,,it burns your eyes \Nand stings your nostrils.
Dialogue: 0,0:00:17.11,0:00:19.68,Default,,0000,0000,0000,,You could stare at the bright\Nflames forever
Dialogue: 0,0:00:19.68,0:00:23.73,Default,,0000,0000,0000,,as they twist and flicker \Nin endless incarnations.
Dialogue: 0,0:00:23.73,0:00:25.94,Default,,0000,0000,0000,,But what exactly are you looking at?
Dialogue: 0,0:00:25.94,0:00:28.56,Default,,0000,0000,0000,,The flames are obviously not solid,
Dialogue: 0,0:00:28.56,0:00:29.98,Default,,0000,0000,0000,,nor are they liquid.
Dialogue: 0,0:00:29.98,0:00:33.07,Default,,0000,0000,0000,,Mingling with the air, they’re \Nmore like a gas,
Dialogue: 0,0:00:33.07,0:00:35.42,Default,,0000,0000,0000,,but more visible--and more fleeting.
Dialogue: 0,0:00:35.42,0:00:39.42,Default,,0000,0000,0000,,And on a scientific level, \Nfire differs from gas
Dialogue: 0,0:00:39.42,0:00:43.42,Default,,0000,0000,0000,,because gases can exist in \Nthe same state indefinitely
Dialogue: 0,0:00:43.42,0:00:47.37,Default,,0000,0000,0000,,while fires always burn out eventually.
Dialogue: 0,0:00:47.37,0:00:50.64,Default,,0000,0000,0000,,One misconception is that\Nfire is a plasma,
Dialogue: 0,0:00:50.64,0:00:53.44,Default,,0000,0000,0000,,the fourth state of matter in which atoms
Dialogue: 0,0:00:53.44,0:00:55.99,Default,,0000,0000,0000,,are stripped of their electrons.
Dialogue: 0,0:00:55.99,0:00:58.100,Default,,0000,0000,0000,,Like fire and unlike the\Nother kinds of matter,
Dialogue: 0,0:00:58.100,0:01:03.42,Default,,0000,0000,0000,,plasmas don’t exist in a stable\Nstate on earth.
Dialogue: 0,0:01:03.42,0:01:08.56,Default,,0000,0000,0000,,They only form when gas is exposed\Nto an electric field or superheated
Dialogue: 0,0:01:08.56,0:01:13.38,Default,,0000,0000,0000,,to temperatures of thousands \Nor tens of thousands of degrees.
Dialogue: 0,0:01:13.38,0:01:16.59,Default,,0000,0000,0000,,By contrast, fuels like wood \Nand paper burn
Dialogue: 0,0:01:16.59,0:01:19.23,Default,,0000,0000,0000,,at a few hundred degrees —far below the
Dialogue: 0,0:01:19.23,0:01:24.22,Default,,0000,0000,0000,,threshold of what's usually\Nconsidered a plasma.
Dialogue: 0,0:01:24.22,0:01:27.36,Default,,0000,0000,0000,,So if fire isn’t a solid, liquid, gas,
Dialogue: 0,0:01:27.36,0:01:30.07,Default,,0000,0000,0000,,or a plasma, what does that leave?
Dialogue: 0,0:01:30.07,0:01:33.58,Default,,0000,0000,0000,,It turns out fire isn’t actually\Nmatter at all.
Dialogue: 0,0:01:33.58,0:01:39.66,Default,,0000,0000,0000,,Instead, it’s our sensory experience of a\Nchemical reaction called combustion.
Dialogue: 0,0:01:39.66,0:01:43.72,Default,,0000,0000,0000,,In a way, fire is like the leaves\Nchanging color in fall,
Dialogue: 0,0:01:43.72,0:01:46.45,Default,,0000,0000,0000,,the smell of fruit as it ripens,
Dialogue: 0,0:01:46.45,0:01:48.89,Default,,0000,0000,0000,,or a firefly’s blinking light.
Dialogue: 0,0:01:48.89,0:01:51.24,Default,,0000,0000,0000,,All of these are sensory clues that a
Dialogue: 0,0:01:51.24,0:01:54.32,Default,,0000,0000,0000,,chemical reaction is taking place.
Dialogue: 0,0:01:54.32,0:01:57.43,Default,,0000,0000,0000,,What differs about fire is that\Nit engages a lot of
Dialogue: 0,0:01:57.43,0:02:00.90,Default,,0000,0000,0000,,our senses at the same time, \Ncreating the kind of vivid
Dialogue: 0,0:02:00.90,0:02:05.52,Default,,0000,0000,0000,,experience we expect to come\Nfrom a physical thing.
Dialogue: 0,0:02:05.52,0:02:08.23,Default,,0000,0000,0000,,Combustion creates that sensory experience
Dialogue: 0,0:02:08.23,0:02:11.85,Default,,0000,0000,0000,,using fuel, heat, and oxygen.
Dialogue: 0,0:02:11.85,0:02:15.70,Default,,0000,0000,0000,,In a campfire, when the logs are \Nheated to their ignition temperature,
Dialogue: 0,0:02:15.70,0:02:18.07,Default,,0000,0000,0000,,the walls of their cells decompose,
Dialogue: 0,0:02:18.07,0:02:22.24,Default,,0000,0000,0000,,releasing sugars and other \Nmolecules into the air.
Dialogue: 0,0:02:22.24,0:02:25.02,Default,,0000,0000,0000,,These molecules then react \Nwith airborne oxygen
Dialogue: 0,0:02:25.02,0:02:27.79,Default,,0000,0000,0000,,to create carbon dioxide and water.
Dialogue: 0,0:02:27.79,0:02:31.54,Default,,0000,0000,0000,,At the same time, any trapped\Nwater in the logs
Dialogue: 0,0:02:31.54,0:02:35.60,Default,,0000,0000,0000,,vaporizes, expands, ruptures \Nthe wood around it,
Dialogue: 0,0:02:35.60,0:02:39.11,Default,,0000,0000,0000,,and escapes with a satisfying crackle.
Dialogue: 0,0:02:39.11,0:02:43.11,Default,,0000,0000,0000,,As the fire heats up, the carbon \Ndioxide and water vapor
Dialogue: 0,0:02:43.11,0:02:45.85,Default,,0000,0000,0000,,created by combustion expand.
Dialogue: 0,0:02:45.85,0:02:50.59,Default,,0000,0000,0000,,Now that they’re less dense,\Nthey rise in a thinning column.
Dialogue: 0,0:02:50.59,0:02:53.85,Default,,0000,0000,0000,,Gravity causes this expansion and rising, \Nwhich gives
Dialogue: 0,0:02:53.85,0:02:56.44,Default,,0000,0000,0000,,flames their characteristic taper.
Dialogue: 0,0:02:56.44,0:02:59.72,Default,,0000,0000,0000,,Without gravity, molecules don’t separate
Dialogue: 0,0:02:59.72,0:03:04.21,Default,,0000,0000,0000,,by density and the flames \Nhave a totally different shape.
Dialogue: 0,0:03:04.21,0:03:06.52,Default,,0000,0000,0000,,We can see all of this because combustion
Dialogue: 0,0:03:06.52,0:03:08.34,Default,,0000,0000,0000,,also generates light.
Dialogue: 0,0:03:08.34,0:03:11.18,Default,,0000,0000,0000,,Molecules emit light when heated,
Dialogue: 0,0:03:11.18,0:03:12.95,Default,,0000,0000,0000,,and the color of the light depends
Dialogue: 0,0:03:12.95,0:03:14.86,Default,,0000,0000,0000,,on the temperature of the molecules.
Dialogue: 0,0:03:14.86,0:03:18.23,Default,,0000,0000,0000,,The hottest flames are white or blue.
Dialogue: 0,0:03:18.23,0:03:20.34,Default,,0000,0000,0000,,The type of molecules in a fire can
Dialogue: 0,0:03:20.34,0:03:22.47,Default,,0000,0000,0000,,also influence flame color.
Dialogue: 0,0:03:22.47,0:03:26.47,Default,,0000,0000,0000,,For instance, any unreacted \Ncarbon atoms from the logs
Dialogue: 0,0:03:26.47,0:03:29.36,Default,,0000,0000,0000,,form little clumps of soot that rise
Dialogue: 0,0:03:29.36,0:03:32.09,Default,,0000,0000,0000,,into the flames and emit the yellow-orange
Dialogue: 0,0:03:32.09,0:03:35.15,Default,,0000,0000,0000,,light we associate with a campfire.
Dialogue: 0,0:03:35.15,0:03:38.23,Default,,0000,0000,0000,,Substances like copper, calcium chloride,
Dialogue: 0,0:03:38.23,0:03:40.23,Default,,0000,0000,0000,,and potassium chloride can add their
Dialogue: 0,0:03:40.23,0:03:43.61,Default,,0000,0000,0000,,own characteristic hues to the mix.
Dialogue: 0,0:03:43.61,0:03:45.61,Default,,0000,0000,0000,,Besides colorful flames,
Dialogue: 0,0:03:45.61,0:03:49.35,Default,,0000,0000,0000,,fire also continues to generate heat\Nas it burns.
Dialogue: 0,0:03:49.35,0:03:52.02,Default,,0000,0000,0000,,This heat sustains the flames by keeping
Dialogue: 0,0:03:52.02,0:03:55.96,Default,,0000,0000,0000,,the fuel at or above ignition temperature.
Dialogue: 0,0:03:55.96,0:03:58.60,Default,,0000,0000,0000,,Eventually, though, even the hottest fires
Dialogue: 0,0:03:58.60,0:04:01.04,Default,,0000,0000,0000,,run out of fuel or oxygen.
Dialogue: 0,0:04:01.04,0:04:04.41,Default,,0000,0000,0000,,Then, those twisting flames\Ngive a final hiss
Dialogue: 0,0:04:04.41,0:04:06.86,Default,,0000,0000,0000,,and disappear with a wisp of smoke
Dialogue: 0,0:04:06.86,0:04:09.21,Default,,0000,0000,0000,,as if they were never there at all.