Purpose - To demonstrate the force of attraction betweencharged particles.
Materials - modeling clay coin
balloon, small enough to hold in your hand
■ Press a walnut-sized piece of clayonto a table.
■ Push the edge of the coin into theclay so that the coin stands upright.
■ Balance the toothpick across thetop edge of the standing coin.
■ Charge the balloon by rubbing iton your hair or a wool scarf about 10 times. Your hair must be clean, dry, andoil-free.
■ Hold the charged balloon near, butnot touching, the toothpick.
■ Watch the toothpick for anymovement.
Results The toothpick turns and falls offthe edge
of the coin.
Why? The toothpick, balloon, and hair are all examples of matter, and all matter is made of minuteunits called atoms. Atoms havepositively charged protons in their nucleus (center of an atom) and negatively charged electrons spinning around the nucleus. Theballoon becomes negatively charged on the side that is rubbed on your hairbecause the electrons are rubbed off the hair and collect on the balloon. Thisbuild-up of electrical charges that remain in one place is called static electricity. The negatively charged balloonattracts the positive part of the toothpick. This attraction is strong enoughto pull the wooden stick off the coin.