Rubbing Up Against Static Electricity
IntroductionHave you ever wondered why rubbing a balloon or a blanket—or even a winter hat—on your head makes your hair stand up? The effect is due to static electricity, but how is the static electricity made, and why does it make your hair stand on end?
Static electricity is the buildup of electrical charge in an object. Sometimes static electricity can suddenly discharge, such as when a bolt of lightning flashes through the sky. Other times, static electricity can cause objects to cling to one another. Think of how socks fresh out of the dryer stick together. This happens when objects have opposite charges, positive and negative, which attract. (Objects with the same charges repel one another.) Could enough static electricity make a balloon stick to a wall? How much do you think you would have to rub it?
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BackgroundWhen one object is rubbed against another, static electricity can be created. This is because the rubbing creates a negative charge that is carried by electrons. The electrons can build up to produce static electricity. For example, when you shuffle your feet across a carpet, you are creating many surface contacts between your feet and the carpet, allowing electrons to transfer to you, thereby building up a static charge on your skin. When you touch another person or an object, you can suddenly discharge the static as an electrical shock.
Similarly, when you rub a balloon on your head it causes opposite static charges to build up both on your hair and the balloon. Consequently, when you pull the balloon slowly away from your head, you can see these two opposite static charges attracting one another and making your hair stand up.
Extra: Does rubbing in one direction give a different result than rubbing back and forth? Try comparing the same number of rubs in one direction with those done back and forth. Does one stay on the wall longer than the other?
Extra: Try comparing the effectiveness of different materials for producing a static charge. Does rubbing wool work better than rubbing silk? Design an experiment to test several different materials: silk, wool, nylon, polyester, plastic, metal, etcetera.
Observations and ResultsIn general, did the balloon stick to the wall for a longer amount of time as you increased the number of times you rubbed the balloon on the woolly object?
Wool is a conductive material, which means it readily gives away its electrons. Consequently, when you rub a balloon on wool, this causes the electrons to move from the wool to the balloon's surface. The rubbed part of the balloon now has a negative charge. Objects made of rubber, such as the balloon, are electrical insulators, meaning that they resist electric charges flowing through them. This is why only part of the balloon may have a negative charge (where the wool rubbed it) and the rest may remain neutral.
When the balloon has been rubbed enough times to gain a sufficient negative charge, it will be attracted to the wall. Although the wall should normally have a neutral charge, the charges within it can rearrange so that a positively charged area attracts the negatively charged balloon. Because the wall is also an electrical insulator, the charge is not immediately discharged. However, because metal is an electrical conductor, when you rub the balloon against metal the extra electrons in the balloon quickly leave the balloon and move into the metal so the balloon is no longer attracted and does not adhere.
More to Explore"Static Electricity: Learn about Static Charge & Static Shock" from Science Made Simple
"The Shocking Truth Behind Static Electricity" from Live Science
"Static Electricity: Background Information for the Teacher" from The Museum of Science, Boston
"Rubbing Up against Static Electricity" from Science Buddies
Teisha Rowland, PhD, Science Buddies
Science Buddies |
Electricity, electronics, insulators, conductors
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