What happens when you shuffle your feet on the ground that causes an electric shock? 

What about when you go down a playground slide?

Watch to 1:55 in the video below and then discuss the question with your group.

Zap! You just touched a metal doorknob after shuffling your rubber-soled feet across the carpet. Yipes! You've been struck by lightning! Well, not really, but it's the same idea.

Your rubber-soled shoes picked up stray electrons from the carpet. Those electrons built up on your shoes giving them a static charge. (Static means not moving.) Static charges are always "looking" for the first opportunity to "escape," or discharge. Your contact with a metal doorknob—or car handle or anything that conducts electricity—presents that opportunity and the excess electrons jump at the chance.

So, do thunderclouds have rubber shoes? Not exactly, but there is a lot of shuffling going on inside the cloud.

Lightning begins as static charges in a rain cloud. Winds inside the cloud are very turbulent. Water droplets in the bottom part of the cloud are caught in the updrafts and lifted to great heights where the much colder atmosphere freezes them. Meanwhile, downdrafts in the cloud push ice and hail down from the top of the cloud. Where the ice going down meets the water coming up, electrons are stripped off.

It's a little more complicated than that, but what results is a cloud with a negatively charged bottom and a positively charged top. These electrical fields become incredibly strong, with the atmosphere acting as an insulator between them in the cloud.

When the strength of the charge overpowers the insulating properties of the atmosphere, Z-Z-Z-ZAP! Lightning happens.

How does the lightning "know" where to strike?

The electric field "looks" for a doorknob. Sort of. It looks for the closest and easiest path to release its charge. Often lightning occurs between clouds or inside a cloud.

But the lightning we usually care about most is the lightning that goes from clouds to ground—because that's us!

As the storm moves over the ground, the strong negative charge in the cloud attracts positive charges in the ground. These positive charges move up into the tallest objects like trees, telephone poles, and houses. A "stepped leader" of negative charge descends from the cloud seeking out a path toward the ground. Although this phase of a lightning strike is too rapid for human eyes, this slow-motion video shows it happening.

As the negative charge gets close to the ground, a positive charge, called a streamer, reaches up to meet the negative charge. The channels connect and we see the lightning stroke. We may see several strokes using the same path, giving the lightning bolt a flickering appearance, before the electrical discharge is complete.

Rub the upside-down foam plate with the wool cloth. If this is your first time using the foam in an electrostatic experiment, rub it for a full minute. Then charge the pie plan by following the next steps exactly:

The pan is now charged. You can discharge it by touching it with your finger. You’ll hear a snap, feel a shock, and, if the room is dark, see a spark.

When you rub the foam plate with a wool cloth, you charge it negatively. That’s because the foam attracts electrons from the cloth. Often, a plate fresh from the package will start with a positive charge. If it does, you will have to rub the plate long enough to cancel this initial charge before you can begin building a sizable negative charge. By using an electroscope (such as the one you can build with our 

 activity), you can determine whether the foam is positively or negatively charged. Plastic foam or Styrofoam

 is an insulator; it will hold its charge until it is discharged by current leaking into the air or along a moisture film on its surface.

When you place the pie pan on the foam plate, the electrons on the foam repel the electrons on the pan. Since the electrons can’t leave the pie pan because it is completely surrounded by insulating air and foam, the pan remains neutral. If you touch the pie pan while it is near the foam plate, the mobile electrons will be pushed off the pan and onto you. The electrons make a spark as they jump a few millimeters through the air to reach your finger. The air in the spark is ionized as the moving electrons knock other electrons off air molecules. The ionized air emits light and sound. You can also feel the flow of electrons through your finger.

After the electrons leap to your finger, the pan has a positive charge. Physicists say the pan has been charged by induction. You can carry the positively charged pan around by its handle and carry the positive charge to other objects. For example, if you bring the positively charged pan near your finger again, or near any object that can be a source of electrons, the pan will attract electrons, creating a second spark.

 below to draw a model of what is happening in the pie tin shock experiment. Add your drawing to your notebook and include an explanation of how and why the shock happens.

Based on what we learned this week, why do you think the pie tins fly off of the Van De Graff Generator? Explain as completely as you can. 

Learn about charge transfer and electric shock

Charge Transfer