[Script Info]
Title: 
[Events]
Format: Layer, Start, End, Style, Name, MarginL, MarginR, MarginV, Effect, Text
Dialogue: 0,0:00:08.05,0:00:10.70,Default,,0000,0000,0000,,This is a crystal of sugar.
Dialogue: 0,0:00:10.70,0:00:14.49,Default,,0000,0000,0000,,If you press on it, it will actually\Ngenerate its own electricity.
Dialogue: 0,0:00:14.49,0:00:17.80,Default,,0000,0000,0000,,How can this simple crystal \Nact like a tiny power source?
Dialogue: 0,0:00:17.80,0:00:20.39,Default,,0000,0000,0000,,Because sugar is piezoelectric.
Dialogue: 0,0:00:20.39,0:00:23.15,Default,,0000,0000,0000,,Piezoelectric materials \Nturn mechanical stress,
Dialogue: 0,0:00:23.15,0:00:24.33,Default,,0000,0000,0000,,like pressure,
Dialogue: 0,0:00:24.33,0:00:25.19,Default,,0000,0000,0000,,sound waves,
Dialogue: 0,0:00:25.19,0:00:26.25,Default,,0000,0000,0000,,and other vibrations
Dialogue: 0,0:00:26.25,0:00:28.75,Default,,0000,0000,0000,,into electricity and vice versa.
Dialogue: 0,0:00:28.75,0:00:30.65,Default,,0000,0000,0000,,This odd phenomenon was first\Ndiscovered
Dialogue: 0,0:00:30.65,0:00:34.97,Default,,0000,0000,0000,,by the physicist Pierre Curie \Nand his brother Jacques in 1880.
Dialogue: 0,0:00:34.97,0:00:38.42,Default,,0000,0000,0000,,They discovered that if they compressed\Nthin slices of certain crystals,
Dialogue: 0,0:00:38.42,0:00:43.02,Default,,0000,0000,0000,,positive and negative charges would appear\Non opposite faces.
Dialogue: 0,0:00:43.02,0:00:45.16,Default,,0000,0000,0000,,This difference in charge, or voltage,
Dialogue: 0,0:00:45.16,0:00:48.93,Default,,0000,0000,0000,,meant that the compressed crystal\Ncould drive current through a circuit,
Dialogue: 0,0:00:48.93,0:00:50.49,Default,,0000,0000,0000,,like a battery.
Dialogue: 0,0:00:50.49,0:00:52.72,Default,,0000,0000,0000,,And it worked the other way around, too.
Dialogue: 0,0:00:52.72,0:00:56.88,Default,,0000,0000,0000,,Running electricity through these crystals\Nmade them change shape.
Dialogue: 0,0:00:56.88,0:00:57.98,Default,,0000,0000,0000,,Both of these results,
Dialogue: 0,0:00:57.98,0:01:00.77,Default,,0000,0000,0000,,turning mechanical energy into electrical,
Dialogue: 0,0:01:00.77,0:01:03.16,Default,,0000,0000,0000,,and electrical energy into mechanical,
Dialogue: 0,0:01:03.16,0:01:04.70,Default,,0000,0000,0000,,were remarkable.
Dialogue: 0,0:01:04.70,0:01:08.15,Default,,0000,0000,0000,,But the discovery went uncelebrated\Nfor several decades.
Dialogue: 0,0:01:08.15,0:01:11.15,Default,,0000,0000,0000,,The first practical application\Nwas in sonar instruments
Dialogue: 0,0:01:11.15,0:01:14.65,Default,,0000,0000,0000,,used to detect German submarines\Nduring World War I.
Dialogue: 0,0:01:14.65,0:01:17.46,Default,,0000,0000,0000,,Piezoelectric quartz crystals \Nin the sonar's transmitter
Dialogue: 0,0:01:17.46,0:01:21.46,Default,,0000,0000,0000,,vibrated when they were subjected\Nto alternating voltage.
Dialogue: 0,0:01:21.46,0:01:23.95,Default,,0000,0000,0000,,That sent ultrasound waves\Nthrough the water.
Dialogue: 0,0:01:23.95,0:01:27.18,Default,,0000,0000,0000,,Measuring how long it took these waves\Nto bounce back from an object
Dialogue: 0,0:01:27.18,0:01:29.85,Default,,0000,0000,0000,,revealed how far away it was.
Dialogue: 0,0:01:29.85,0:01:31.53,Default,,0000,0000,0000,,For the opposite transformation,
Dialogue: 0,0:01:31.53,0:01:34.01,Default,,0000,0000,0000,,converting mechanical energy \Nto electrical,
Dialogue: 0,0:01:34.01,0:01:36.83,Default,,0000,0000,0000,,consider the lights that turn on\Nwhen you clap.
Dialogue: 0,0:01:36.83,0:01:39.54,Default,,0000,0000,0000,,Clapping your hands send sound vibrations\Nthrough the air
Dialogue: 0,0:01:39.54,0:01:43.19,Default,,0000,0000,0000,,and causes the piezo element to bend\Nback and forth.
Dialogue: 0,0:01:43.19,0:01:46.88,Default,,0000,0000,0000,,This creates a voltage that can drive\Nenough current to light up the LEDs,
Dialogue: 0,0:01:46.88,0:01:50.42,Default,,0000,0000,0000,,though it's conventional sources \Nof electricity that keep them on.
Dialogue: 0,0:01:50.42,0:01:53.63,Default,,0000,0000,0000,,So what makes a material piezoelectric?
Dialogue: 0,0:01:53.63,0:01:55.75,Default,,0000,0000,0000,,The answer depends on two factors:
Dialogue: 0,0:01:55.75,0:01:57.59,Default,,0000,0000,0000,,the materials atomic structure,
Dialogue: 0,0:01:57.59,0:02:00.97,Default,,0000,0000,0000,,and how electric charge\Nis distributed within it.
Dialogue: 0,0:02:00.97,0:02:02.69,Default,,0000,0000,0000,,Many materials are crystalline,
Dialogue: 0,0:02:02.69,0:02:04.50,Default,,0000,0000,0000,,meaning they're made of atoms or ions
Dialogue: 0,0:02:04.50,0:02:07.63,Default,,0000,0000,0000,,arranged in an orderly \Nthree-dimensional pattern.
Dialogue: 0,0:02:07.63,0:02:10.27,Default,,0000,0000,0000,,That pattern has a building block\Ncalled a unit cell
Dialogue: 0,0:02:10.27,0:02:12.73,Default,,0000,0000,0000,,that repeats over and over.
Dialogue: 0,0:02:12.73,0:02:15.56,Default,,0000,0000,0000,,In most non-piezoelectric \Ncrystalline materials,
Dialogue: 0,0:02:15.56,0:02:18.61,Default,,0000,0000,0000,,the atoms in their unit cells\Nare distributed symmetrically
Dialogue: 0,0:02:18.61,0:02:20.47,Default,,0000,0000,0000,,around a central point.
Dialogue: 0,0:02:20.47,0:02:23.95,Default,,0000,0000,0000,,But some crystalline materials\Ndon't possess a center of symmetry
Dialogue: 0,0:02:23.95,0:02:27.10,Default,,0000,0000,0000,,making them candidates \Nfor piezoelectricity.
Dialogue: 0,0:02:27.10,0:02:28.52,Default,,0000,0000,0000,,Let's look at quartz,
Dialogue: 0,0:02:28.52,0:02:31.98,Default,,0000,0000,0000,,a piezoelectric material \Nmade of silicon and oxygen.
Dialogue: 0,0:02:31.98,0:02:36.72,Default,,0000,0000,0000,,The oxygens have a slight negative charge\Nand silicons have a slight positive,
Dialogue: 0,0:02:36.72,0:02:38.25,Default,,0000,0000,0000,,creating a separation of charge,
Dialogue: 0,0:02:38.25,0:02:41.14,Default,,0000,0000,0000,,or a dipole along each bond.
Dialogue: 0,0:02:41.14,0:02:43.57,Default,,0000,0000,0000,,Normally, these dipoles \Ncancel each other out,
Dialogue: 0,0:02:43.57,0:02:46.59,Default,,0000,0000,0000,,so there's no net separation of charge\Nin the unit cell.
Dialogue: 0,0:02:46.59,0:02:49.57,Default,,0000,0000,0000,,But if a quartz crystal is squeezed\Nalong a certain direction,
Dialogue: 0,0:02:49.57,0:02:51.38,Default,,0000,0000,0000,,the atoms shift.
Dialogue: 0,0:02:51.38,0:02:54.13,Default,,0000,0000,0000,,Because of the resulting asymmetry\Nin charge distribution,
Dialogue: 0,0:02:54.13,0:02:56.63,Default,,0000,0000,0000,,the dipoles no longer cancel\Neach other out.
Dialogue: 0,0:02:56.63,0:03:00.46,Default,,0000,0000,0000,,The stretched cell ends up\Nwith a net negative charge on one side
Dialogue: 0,0:03:00.46,0:03:03.13,Default,,0000,0000,0000,,and a net positive on the other.
Dialogue: 0,0:03:03.13,0:03:06.28,Default,,0000,0000,0000,,This charge imbalance is repeated\Nall the way through the material,
Dialogue: 0,0:03:06.28,0:03:09.94,Default,,0000,0000,0000,,and opposite charges collect\Non opposite faces of the crystal.
Dialogue: 0,0:03:09.94,0:03:13.87,Default,,0000,0000,0000,,This results in a voltage that can\Ndrive electricity through a circuit.
Dialogue: 0,0:03:13.87,0:03:16.91,Default,,0000,0000,0000,,Piezoelectric materials can \Nhave different structures.
Dialogue: 0,0:03:16.91,0:03:21.52,Default,,0000,0000,0000,,But what they all have in common is unit\Ncells which lack a center of symmetry.
Dialogue: 0,0:03:21.52,0:03:24.35,Default,,0000,0000,0000,,And the stronger the compression\Non piezoelectric materials,
Dialogue: 0,0:03:24.35,0:03:26.74,Default,,0000,0000,0000,,the larger the voltage generated.
Dialogue: 0,0:03:26.74,0:03:29.96,Default,,0000,0000,0000,,Stretch the crystal, instead,\Nand the voltage will switch,
Dialogue: 0,0:03:29.96,0:03:32.24,Default,,0000,0000,0000,,making current flow the other way.
Dialogue: 0,0:03:32.24,0:03:35.72,Default,,0000,0000,0000,,More materials are piezoelectric\Nthan you might think.
Dialogue: 0,0:03:35.72,0:03:36.66,Default,,0000,0000,0000,,DNA,
Dialogue: 0,0:03:36.66,0:03:37.40,Default,,0000,0000,0000,,bone,
Dialogue: 0,0:03:37.40,0:03:38.27,Default,,0000,0000,0000,,and silk
Dialogue: 0,0:03:38.27,0:03:42.43,Default,,0000,0000,0000,,all have this ability to turn\Nmechanical energy into electrical.
Dialogue: 0,0:03:42.43,0:03:45.90,Default,,0000,0000,0000,,Scientists have created a variety\Nof synthetic piezoelectric materials
Dialogue: 0,0:03:45.90,0:03:49.33,Default,,0000,0000,0000,,and found applications for them\Nin everything from medical imaging
Dialogue: 0,0:03:49.33,0:03:51.54,Default,,0000,0000,0000,,to ink jet printers.
Dialogue: 0,0:03:51.54,0:03:54.84,Default,,0000,0000,0000,,Piezoelectricity is responsible for \Nthe rhythmic oscillations
Dialogue: 0,0:03:54.84,0:03:57.98,Default,,0000,0000,0000,,of the quartz crystals\Nthat keep watches running on time,
Dialogue: 0,0:03:57.98,0:03:59.85,Default,,0000,0000,0000,,the speakers of musical birthday cards,
Dialogue: 0,0:03:59.85,0:04:03.00,Default,,0000,0000,0000,,and the spark that ignites the gas \Nin some barbecue grill lighters
Dialogue: 0,0:04:03.00,0:04:05.12,Default,,0000,0000,0000,,when you flick the switch.
Dialogue: 0,0:04:05.12,0:04:08.35,Default,,0000,0000,0000,,And piezoelectric devices may become\Neven more common
Dialogue: 0,0:04:08.35,0:04:12.99,Default,,0000,0000,0000,,since electricity is in high demand\Nand mechanical energy is abundant.
Dialogue: 0,0:04:12.99,0:04:15.94,Default,,0000,0000,0000,,There are already train stations\Nthat use passengers' footsteps
Dialogue: 0,0:04:15.94,0:04:18.48,Default,,0000,0000,0000,,to power the ticket gates and displays
Dialogue: 0,0:04:18.48,0:04:22.10,Default,,0000,0000,0000,,and a dance club where piezoelectricity\Nhelps power the lights.
Dialogue: 0,0:04:22.10,0:04:25.35,Default,,0000,0000,0000,,Could basketball players running back\Nand forth power the scoreboard?
Dialogue: 0,0:04:25.35,0:04:28.67,Default,,0000,0000,0000,,Or might walking down the street\Ncharge your electronic devices?
Dialogue: 0,0:04:28.67,0:04:31.24,Default,,0000,0000,0000,,What's next for piezoelectricity?