Girls and boys, start your balloons! In this week's Saturday Science, brought to you by Exploratorium, discover why rubbing a balloon on your head will make a soda can race across a room.
- Empty soda can
- Blown-up balloon
- Your hair
- Put the can on its side on a table top or the floor -- any place that's flat and smooth. Hold it with your finger until it stays still.
- Rub the balloon back and forth on your hair really fast.
- Hold the balloon about an inch in front of the can. The can will start to roll, even though you're not touching it!
- Move the balloon away from the can—slowly—and the can will follow the balloon.
- If you move the balloon to the other side of the can, the can will roll in the other direction.
- How fast will the can roll? How far can you roll it before the can stops? Will it roll uphill?
- If you have some friends with cans and balloons, you can have a race across the room or down the sidewalk.
Rub a balloon on your head and you can...
- Bend water!
Turn on the faucet in your bathroom or kitchen. Don't run the water too hard, but more than a little trickle. Now rub a balloon on your head and hold the balloon near the water. The stream of water will bend toward the balloon!
- Give yourself funny hair!
Rub the balloon on your head, then pull it away. Your hair will stick out and look really funny. (This can also happen when you comb your hair with a plastic comb.) What if you hold the balloon near your arm? Can you feel the hairs on your arm move? Will it work on doll hair? How about animal fur?
- Stick the balloon to your face!
Once you've rubbed the balloon on your head, it will stick to other things—with no glue. You can stick it to the wall, to the TV, or even to your face!
Why does the soda can roll? Basically, you pile up electrons on one thing and use them to attract the protons in something else. When you rub a balloon on your hair, it ends up loaded with electrons. Those electrons can attract the protons in a soda can, the protons in a trickle of water, the protons in your hair, or the protons in a wall.
Why do clothes stick together in the dryer? The attraction between protons and electrons can also make clothes stick together in the dryer. When you dry clothes in the dryer, different fabrics rub together, and electrons from a cotton sock (for instance) may rub off onto a polyester shirt. That's why clothes sometimes stick together and make sparks when you pull them apart. You may have used antistatic sheets in your dryer. As these sheets bounce around with your clothes, they add a uniform antistatic coating to the fabric. Rather than cotton rubbing against polyester, you've got the antistatic coating on the cotton rubbing against the antistatic coating on the polyester. No electrons rub off-and you don't get any static cling.