Key Concepts
Electric Charge
Polarity
Attraction
Repulsion

Introduction
Have you ever felt a shock when you tap someone on the shoulder or touch a car door? How about seen sparks when you comb your hair or rubbed a fleece blanket on a cold day? If you have, then you've felt the effects of static electricity! In this activity you'll learn how to use static electricity to make bits of paper jump up and down.

Background
Everything is made of tiny building blocks called atoms. Although atoms are already microscopic, they contain even smaller particles called electrons, protons and neutrons. Electrons carry a negative charge and protons carry a positive charge whereas neutrons have no charge. There are usually an equal number of electrons and protons in an atom, and the atom is therefore is considered “neutral.” But, if an atom gains electrons, it becomes “negatively charged.” If it loses electrons, it becomes “positively charged.” Atoms with the same charges repel one another and atoms with unlike charges are attracted to one another.

Materials

• Sheet of Plexiglas™ or other clear plastic (about one-foot square and one-quarter-inch thick); the plastic lid from a storage container, large takeout container or poster frame can also work well
• Four supports about one to two inches high (Tuna cans work nicely.)
• Tiny bits of paper, Styrofoam, puffed rice, plain dry rice grains or confetti
• Pieces of different types of fabric, including wool
• Flat, smooth table or countertop surface where you can conduct the activity

Preparation

• Scatter the paper, Styrofoam, rice or confetti on a small section of a table.
• Set up the supports—to reach the four corners of your plastic—around the bits of material.
• Place the plastic sheet on the supports. (The small pieces of material should be below the plastic sheet.)

Procedure

• What are the small bits of material under the plastic doing?
• “Charge” the plastic by rubbing it vigorously with the piece of wool.
• Watch the bits! What are they doing? How long did they “dance”?
• Try charging the plastic by rubbing different types of material on it, including your hand. What material made the bits dance the longest?
• Extra: Remove the bits of paper, Styrofoam, rice or confetti and scatter a different type of material under the plastic. Repeat the process of charging the plastic. Are these new bits more active than the previous ones? Which bits were most active? Why?

Observations and results
Both the plastic and the small bits start out electrically neutral. That is, they have a roughly equal number of protons and electrons. When you rub the plastic with the wool cloth, the wool transfers negative charges (electrons) to the plastic, making it negatively charged.

These negative charges polarize the bits, making one side of the paper, Styrofoam, rice or confetti positive and the other side negative, attracting the positive charges to the tops of the bits and pushing the negative charges away, to the bottoms. The attraction between the negative plastic and the positive charge concentrated on the top of the bits makes them “jump” up to the underside of the plastic.

But, when a bit actually touches the plastic, some of the plastic's negative charge flows to the bit. Because the whole bit of material was originally neutral, the bit now has excess negative charge. The negatively charged bit and the negatively charged plastic now repel each other, which causes it to “jump” quickly back to the table.

As the bit's excess negative charge slowly drains away to the tabletop or the air, the bit again becomes neutral and is ready to jump up to the plastic once more, making the group of bits appear to dance. Over time, the negative charge of the plastic dissipates—until you recharge it by rubbing it again!

More to Explore
How Does Static Electricity Work?, from the Library of Congress
Super Sparker, from Exploratorium
Remote-Control Roller, from Exploratorium
Attraction with Static Electricity, from Scientific American

This activity brought to you in partnership with Exploratorium