The Science of Lightning
Static electricity is fun to play with – unless it's a ten million-volt lightning strike!
The word “static” means something that’s not moving or not changing. A static charge is electricity that’s not moving. Instead, it builds up on the surface of something like a fingertip or a cloud. It may not move but it causes other things to move and can create a tiny blue spark at your fingertip or a blinding blast of white in the sky!
- 1-liter plastic bottle and cap
- Foam beads, 1/8" (3 mm) diameter
- Balloons (latex or rubber)
- Small piece of paper or aluminum foil (optional)
- Small kitchen funnel (optional)
- Wool sweater (optional)
- Adult supervision
You need a layer of foam beads inside the bottle. Unfortunately, the little spheres don’t always cooperate. They end up clinging to everything but the inside of the bottle! You can make a pour spout with a piece of paper or aluminum foil and slowly pour beads into the 1-liter bottle. Using a small kitchen funnel for this can be helpful, too.
Cap the bottle so the beads you’ve captured don’t escape. Notice the beads are scattered everywhere clinging to the inside wall of the the bottle. You can shake and tap the bottle any way you want to move all the beads to the bottom but nothing seems to work.
Set the bottle on the table and bring a finger close to but not touching it. How do the beads react to your finger without your even touching the bottle? Some move quickly away from your finger, but c’mon, you didn’t actually touch anything!
Rub the bottle in one direction against a piece of wool or in your hair (if your hair is clean and dry). Hold a finger near the bottle again and look for movement in the beads. Which way do they move this time? Toward your finger or away from it?
Now, do the balloon test. Blow up a balloon and rub it one way several times in clean hair and then hold it close to the bottle. How do the beads react now? Which way do they move? Toward the balloon or away from it? Also, what happens to your hair near the balloon?
Hold the balloon on the knotted end and rub the bottom of the balloon in one direction in your hair or on the wool. Hold the rubbed spot of the balloon near the bottle. Which way do the beads move? Rotate the balloon between its bottom and its side near the bottle and watch the beads. That’s strange!
How Does It Work
By rubbing the balloon in one direction on wool or in your hair, you build up a static electric charge on its surface. In fact, you’re creating and then revealing two different charges. Electrons have a negative (–) charge and protons have a positive (+) charge. Electrons build up on the surface of the balloon where it was rubbed. They pile up in one place and don’t move because the balloon material (the latex) doesn’t let them. This “pile” of negative electrons pulls on the positive protons in the beads because unlike charges attract or pull towards each other. Like charges (either positive and positive or negative and negative) repel or push away from each other. You can explain the movement of the beads by describing the types of charges involved.
When you rub the balloon in your hair, it causes opposite charges to build on your hair and in one place on the balloon. When you slowly pull it away from your hair, you can see these two opposite charges attracting which causes your hair reach for the balloon. You may hear a pop and crackle, too. That’s the charge jumping from one surface to the other. Lighting makes the same jump only it moves from a cloud to the ground (or the other way) and it doesn’t crackle, it booms! With the balloon out of your hair, there’s mostly the same charge in your hair. That means the hairs repel each other and try to separate as far as they can. A little water gets everything back to normal very quickly.
Take It Further
What is Lightning? Lightning is a huge charge of static electricity that can reach from clouds to ground or to other clouds. When a charge gets close to the surface, an upward flow (called a streamer) can rise up through a building, a tree, or even a person. Lightning can start range and forest fires and it’s powerful enough to destroy property. It can seriously hurt or even kill people and animals. However, in addition to balancing atmospheric charges, one of its benefits is that lightning showers nitrogen onto the soil for plants to use.
Lightning Is Really Dangerous! There are countless lightning strikes every day all over the Earth. Scientists think that lightning hits somewhere on Earth about 100 times every second. As a result, around the world more people are killed by lightning than by any other kind of weather-related storm, including hurricanes and tornadoes. Every year, about 100 people are killed by lightning in the US. In the whole world, lightning kills more than 1,000 people a year. A lot more people are hurt by lightning than are killed by it and most of those are hurt very badly.
How Far Away is the Lightning? Use the Flash-to-Bang Rule Count the seconds between the lightning’s “flash” and the “bang” of its thunder. Each five seconds is about one mile. Example: If you see lightning and it takes 10 seconds to hear the thunder, then the lightning is about 2 miles away. (By the way, Hollywood never gets this right. For them, every flash-to-bang is instantaneous which means the lightning is always right on top of the characters.)
How Much Time do I Need to Find a Safe Location? You should seek shelter if the flash-to-bang time is 30 seconds or less. You shouldn’t go out again until 30 minutes after the last thunder clap. This is sometimes called the 30/30 Rule.
Lightning Facts: “When thunder roars, go indoors!”
- Florida ranks first in the US for lightning strikes, with an average of 100 thunderstorm-days per year.
- The populated lightning capital of the world is the west coast of Africa, where as many as 295 thunderstorm-days occur per year. This is also the area where Atlantic Ocean hurricanes are spawned.
- The number of thunderstorms occurring in the US is about 100,000 per year.
- The number of thunderstorms occurring around the Earth is about 2,000 at any given moment.
- Lightning is extremely hot—a flash can instantly heat the air in its pathway to temperatures five times hotter than the Sun’s surface.
- The number of lightning strikes in the US per year is about 25 million.
- A typical lightning bolt contains 1 billion volts and contains between 10,000 to 200,000 amps of current. That compares to 120 volts and 15 amps found in the outlets of your home.
- When the lower end of a lightning bolt comes within about 150 feet (46 meters) of a positively charged object on the surface, it’s met by a climbing surge of positive electricity (called a “streamer”) which can rise up through a building, a tree, or even a person. You get it coming and going.
- Lightning will strike the same place again and again, especially if the location is tall and isolated.
- Nowhere outside is safe when thunderstorms are close by. Run into a safe building or vehicle when you first hear thunder, see lightning, or observe dark threatening clouds developing overhead.
- Positive lightning can flash more than 10 miles (16 km) from the storm cloud where it began to strike “out of the blue” on unprepared people.
Additional information on lightning and lightning safety can be found at the National Oceanic and Atmospheric Administration’s site. http://www.lightningsafety.noaa.gov/outreach.shtml.
There’s information on the National Geographic website as well. http://www.nationalgeographic.com/environment/natural-disasters/lightning/
When thunder roars, go indoors!