Have you ever rubbed a balloon on your head? Why does rubbing a balloon on your head make your hair stand up on end?
When you rub the balloon, electrons move from the atoms and molecules in your hair onto the balloon. Electrons have a negative charge, so the balloon becomes negatively charged and your hair is left with a positive charge. This "separation of charge" is the reason for the collection of effects we call static electricity.
Students will explore static electricity through a series of demonstrations and experiments.
- Describe the movement of electrons from one material to another.
- Determine the resulting charge of two materials rubbing together.
- Explain how static charge causes materials to attract or repel each other.
Everything we see is made up of tiny little parts called atoms. The atoms are made of even smaller parts. These are called protons, electrons, and neutrons. An atom usually has the same number of protons and electrons. Sometimes electrons can be moved away from their atoms. If you comb your hair, electrons leave the atoms and the molecules in your hair and stay on the plastic comb. Electrons have a negative charge. The comb, covered in electrons, becomes negatively charged as well, and your hair is left with the positive charge. This "separation of charge" is the reason for the collection of effects we call static electricity.
If two objects have different charges, they attract (or pull towards) each other. If two objects have the same charge, they repel (or push away) from each other. After you've combed your hair, each of the hairs has the same positive charge. Things with the same charge repel each other. So the hairs try to move away from each other by standing up and away from all the other hairs.
If you walk across a carpet, electrons move from the rug to you. Now you have extra electrons. If you've got extra electrons piled on you, they will spill off when you touch an object like a doorknob, and give you a shock. Shocks come from gaining or losing electric charge in a hurry.
When a charged object is brought close to a neutral material, the electrons on the neutral material will either move toward the charged object (if it has a positive charge) or away from the charged object (if it has a negative charge). In other words, the charges on the neutral object are separated by the nearby charged object. This phenomenon is called an induced charge.
The result is that a normally neutral material will have a slight charge when the charged object approaches. It is enough for the two to attract.
Electrostatic charges are not caused by friction, although many assume this to be the case.
Rubbing a balloon on your head or dragging your feet on the carpet will build up a charge, but so will ordinary walking or repeatedly touching your head with a balloon! It's the contact between two different materials that causes charge to move from one object to another. Rubbing materials together can help move charge more quickly because more surface area is being contacted. Friction has nothing to do with the charge.
An important thing to consider when doing any of these activities is the weather: humidity in the air can make it difficult to build up charges, causing experiments to behave in unexpected ways! The best "static" weather is clear, sunny, and cool.
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