what is lightning? a gigantic electrostatic discharge between the cloud and the ground, between...
TRANSCRIPT
What is lightning?
• a gigantic electrostatic discharge between the cloud and the ground, between clouds, or within a cloud
• the same kind of electricity that can shock you when you touch a doorknob (static electricity)
• results from buildup and discharge of electrical energy between positively and negatively charged areas.
Lightning strikes somewhere on Earth 100 times every second!
Each year lightning strikes
the USA 20 million times!
Most cloud to ground lightning – central FloridaAlmost no lightning – Pacific Northwest
How Does Lightning Work?
1. Wind creates friction in an ice cloud that creates “static electricity.” The bottom of a cloud becomes negatively charged. Since opposites attract, positive charges collect on the ground and other surfaces under the cloud.
How Does Lightning Work?
2. A stepped leader —a negative electrical charge made of zig-zagging segments, or steps—comes partway down from the cloud. The steps are invisible. Each step is about 150 feet long.
How Does Lightning Work?
3. When the stepped leader gets within 150 feet of a positive charge, a streamer (a surge of positive electricity) rises to meet it. The leader and the streamer make a channel.
How Does Lightning Work?
4. An electrical current from an object on the ground surges upward through the channel. It touches off a bright display called a return stroke.
In this 5 minute time exposure photo, lightning strikes Tucson, AZ. Each flash
contains 1 billion volts of electricity, enough to light a
100 watt bulb for 3 months.
Results of Lightning
• A lightning flash happens in ½ a second. In that instant, the lightning flash superheats the surrounding air to 50,000 ºF, five times hotter than the surface of the sun!
• The rapid heating and cooling of air near the lightning channel causes a shock wave that results in thunder.– Thunder - the booming sound produced by rapidly expanding
and vibrating air along the path of the lightning.
• Sound travels more slowly than light, so we see the lightning before we hear the thunder.
Ball lightning occurs after a ground flash.
The ball is usually red, orange, or yellow, and can be as small as a
grapefruit or as big as a pumpkin. The ball
hovers or darts briefly, fizzles out and ends
with a loud
BANG!
Spider lightning flashes crawl across the sky for
up to 90 miles.
Benjamin Franklin
• In 1752 the famous scientist and statesman conducted an experiment to find out if lightning was electricity. During a thunderstorm in Philadelphia, PA, Franklin and his son William flew a homemade kite with a wire attached to it. Franklin expected lightning to strike the wire, then flow down the kite string to a key tied near the end.
Benjamin Franklin
• The kite entered a rain cloud. Franklin touched his knuckle to the key. Zap! An electric spark! The experiment had worked. The lightning behaved like electricity. Franklin had been lucky. If the lightning strike had been stronger, he could have been hurt or killed.
• The church tower of many European cities, usually the highest structure, was the building most often hit by lightning. The buildings burned. Parishioners were told NOT to go to the church to seek shelter during a storm.
• Lightning starts many fires in the western US and Alaska.
• After his experiments, Franklin invented lightning rods to protect buildings.
An early form of lightning protector
shows how the electricity is sent
to the ground where it
dissipates.
More modern lightning rods use guide wires to send the electrical charge safely into
the ground.
Parents “ground” their children. Get it?
Lightning Safety FUN FACT
The Empire State Building in New York City is struck on average more than 100 times per year. The building is actually designed to simulate a giant lightning rod in order to help protect the other buildings in the surrounding area.
Where and when are you most likely to be struck?
• Florida has twice as many lightning casualties as any other state.
• Most lightning casualties occur between noon and 4 p.m. Sunday has 24% more deaths than other days, followed by Wednesday. Lightning reports reach their peak in July.
Who is most likely to be struck?
• Men are struck by lightning 4 times more often than women. Males account for 84% of lightning fatalities and 82% of injuries.
• Only 10-20 percent of lightning victims are immediately struck dead.
• Many doctors do not fully understand how to treat the injuries of the other 80% - 90% of lightning victims who survive a strike.
• The pathology of lightning, or keraunopathy, is known only to a few specialists.
What are the results of being struck by lightning?
• Many lightning victims had been walking in an open field or swimming before they were struck. Other lightning victims had been holding metal objects such as golf clubs, fishing rods, hay forks, or umbrellas.
• They suffer from paralysis, memory loss, burns, loss of sight or hearing and other neurological problems.
Where is it?
• Count the seconds between a flash of lightning and the next clap of thunder.
• Divide by 5 to determine the distance to the lightning in miles.
• By the time you hear thunder, you are already within striking distance!
How far away is it?
• You see lightning and begin counting.
• You count to 10.
• How far away is the storm?– 10 divided by 5– equals 2 miles
Thunder
• Lightning emits a broadband pulse of radio waves that our ears cannot detect.
• Picked up by specialized equipment, lightning sounds like bacon frying or the crackling of a campfire.
• Scientists call the sounds tweeks, whistlers and sferics.
• Sometimes lightning bolts escape the ionosphere and travel along Earth’s magnetic field!
Lightning Safety• Severe damage can be done by lightning and
certain safety procedures should be followed.
Lightning Safety
• Get into a large building or enclosed vehicle.• Stay off corded phones, computers and other
electrical equipment.• Stay away from water in pools, tubs, showers,
and plumbing.• Install surge suppressors and ground fault
protectors to keep appliances safe.• Wait 30 minutes after the last strike before going
out.
Lightning Safety• If you cannot get to a sturdy building…
– Find a low spot away from trees, fences, and poles.– If you are in the woods, take shelter under the shorter
trees.• If you feel your skin tingle or your hair stand on end,
squat low to the ground on the balls of your feet. Make yourself the smallest target possible, and minimize your contact with the ground.
When thunder roars, go indoors!
Fulgurite
• Sometimes when lightning strikes sand, the sand is superheated. It melts and then fuses together to form a fulgurite. These take the form of tubes, sometimes more than half inch in diameter, that look like lightning bolts.
• Rock Fulgurites are formed when lightning strikes the surface of a rock, melting and fusing the rock.
• The melting point of Si02 is 2950 oF.
Fulgurite
True Lightning Stories
• A watermelon on a kitchen table in Arkansas blew up during a thunderstorm in 1987. A clap of thunder caused it to vibrate so fast that it exploded!
• A field of potatoes was struck by lightning. The potatoes were cooked by the strike. After being dug up, they were eaten like baked potatoes!
Lightning Joke
• Teacher: Why is it said that lightning never strikes the same place twice?
• Student: Because after it’s struck once, the same place isn’t there anymore!