Ions in Action

Make pieces of paper fly through the air and stick onto a balloon. Material: A balloon A sheet of paper A hole punch Instructions: Inflate the balloon to a size that fits easily in your hand. Tie a knot in the end of the balloon. Use the hole punch to cut several small circles from the sheet of paper. Rub the balloon back and forth gently on your hair about 10 times. Don't press too hard. Your hair should be clean, dry, and oil-free. Hold the balloon close to, but not touching, the paper circles. Watch what happens.

Don't forget to take off your hat before you rub the balloon on your hair!

	So, Dr. Marc, why does the balloon pick up the confetti? Atoms are the teeny tiny particles that make up all matter. Atoms have even teenier pieces, called electrons, that they wear like coats. Sometimes the atom wears all its coats, sometimes it takes off one or more.
When you rub the balloon on your hair, some of the electrons rub off and stick to the balloon. The electrons have a negative ( - ) electric charge, so the balloon has a negative charge. When atoms are missing electrons (they've taken off a coat or two), we say they have a positive ( + ) charge. The confetti you made has a few electrons missing, so has a slight positive charge. Negative and positive charges attract each other. So, the confetti sticks to the balloon!
Atoms that have either a negative or positive charge we call ions. The Deep Space 1 spacecraft uses an ion engine to propel itself through space! The ion engine contains a gas called xenon (pronounced ZEE-non). The xenon is given a charge, just as the confetti has a charge. Another part of the ion engine is a thin sheet of metal with many little holes in it (sort of like a window screen). This metal screen also has a charge, like the balloon. So the metal screen attracts the xenon ions like the balloon attracts the confetti. The charged metal screen makes the xenon ions move very fast, so they zoom right through the holes and out the other side of the screen. As they shoot out (the action), they push back against the spacecraft (the reaction). This engine uses the same law of nature that makes a regular fuel-burning rocket work. (See how to build a pop-rocket.) The forces of attraction are very strong in ion propulsion. The ions actually move much faster than does the hot gas coming out of a regular rocket engine. So the ion propulsion system works even better! Read the story of Professor Starr's Dream Trip, made possible by the ion engine.