the answer files

Why is the sky blue?

What is lightning?

What are the states of matter?

Does hot water freeze faster than cold?

Why does a can of Coke sink while a can of Diet Coke floats?

Why do you close your eyes when you sneeze?

Why do mosquitoes bite me more than my friends?

Why do your feet stink?

How does gravity work?

How fast does the space shuttle move in orbit?

What is escape velocity?

What would happen if you turned on your headlights while moving at the speed of light?

What is lightning?
Lightning is a kick-butt jolt of electricity that can travel inside a cloud, between clouds, or from a cloud to Earth. lightningThere's no real consensus on how clouds accumulate such huge charges. The Why Files asked David Martin, a scientist at the University of Wisconsin-Madison's Space Science and Engineering Center to explain the most plausible theory.

Photo ©Daniel Robinson

Martin told us that differences in temperature cause updrafts in thunderstorms. These fast vertical winds contain large and small particles of ice, and supercooled water (water that's cold enough to freeze, but has not yet frozen). As the water and ice collide, positive and negative charges separate. The updrafts then move the charges, forming the cloud into a sandwich with negative charges in the middle, and positive ones at the top and bottom.

lightning does strike twice
Map courtesy of National Weather Service, Jackson, Mississippi.

When enough charges accumulate, the resulting electrical potential, or voltage, overcomes the air's electrical resistance and starts a lightning bolt. The first step is a small "leader" stroke that ionizes the air in its path. (Ions are molecules or atoms with an electric charge that can flow to form an electric current). With the ions in place, a much larger return stroke travels up from the Earth to the cloud. Most lightning bolts last less than 1/10 second.

Did you know?

  • In the average year, lightning strikes the United States about 20 million times. Florida is easily the national lightning Mecca.
  • A lightning bolt can carry 30,000 amps at several hundred million volts.
  • On average, lightning kills more people than tornadoes -- 93 Americans each year.
  • Most people who are struck by lightning survive, but the electrical and heating effects can cause a wide range of physical, mental and emotional problems.
  • It's more common to be struck indirectly -- by touching something conductive, say a telephone or an appliance -- than to be struck directly by the bolt.

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The Why Files
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