Get a charge out of static electricity: Learn about why your hair stands on end after pulling off a wool sweater--and how you can use that same energy to make a balloon stick to the wall. Image: George Retseck
Have 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?
When 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.
• An object made out of wool (such as a sweater, scarf, blanket or ball of yarn)
• A wall
• A partner (optional)
• Blow up the balloon and tie off the end.
• Have your partner prepare to use the stopwatch.
• Hold the balloon in a way that your hand covers as little of its surface area as possible, such as by using only your thumb and pointer finger or by gripping the balloon by its neck where it is tied off.
• Rub the balloon on the woolly object once, in one direction.
• Hold the balloon up on the wall with the side that was rubbed against the wool facing the wall, then release it. Does the balloon stay stuck on the wall? If the balloon stays stuck, have your partner immediately start the stopwatch to time how long the balloon remains bound to the wall. If the balloon does not stick, move to the next step.
• Touch the balloon to a metal object. Why do you think this is important to do?
• Repeat the above process but each time increase the number of times you rub the balloon on the woolly object. Rub the balloon in the same direction each time. (Do not rub the balloon back and forth.) How many rubs does it take to make the balloon stick to the wall for a few seconds? What about multiple minutes?
• You can repeat this whole process two more times. Do your observations for each trial match with the previous trials?
• 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.