What happens to a bucket of water if it turns upside down? To find out, each person needs a bucket with a sturdy handle. This experiment can get wonderfully messy, so it's best to do it outside on a nice day. Fill the bucket about ¾ full with water. You are going to make a fast, clockwise circle with your arm. Hold the bucket at your side, swing the bucket forward, over your head, down behind your shoulder and back through the starting point. Continue this motion smoothly for several rotations. The force acting on the water in the bucket is centripetal force, not centrifugal with which it is often confused. Centripetal force is directed to the center of the circle. Without it, the water and bucket would go off in a straight line.
To find out if you can lift a ball off a table without touching it, each person needs a small, rubber ball and a medium-size, wide-mouth canning jar. Place the ball on a large, flat surface, such as a table. Turn the canning jar upside down over the ball. Keeping the jar on the table, start to move the canning jar so the ball moves around the wall of the jar in a circular path. When the ball's circular path is well-established, life the jar off the table, and stop moving the jar. The wall of the canning jar prevents the ball from escaping. The force of the spin is greater than the force of gravity until the ball's speed slows down. When the force of gravity is greater than the force of the spin, the ball drops out of the jar. Try to continue moving the jar after lifting it off the table and see how long you can keep the ball spinning inside.
Experiment with the forces of gravity and air pressure to make a ping pong ball float in the air. You need three ping pong balls and a hand-held hair dryer. Plug in the hair dryer and turn it on the highest setting. Use the cool air setting, if your dryer has one, to minimize the risk of burns. Hold the ping pong ball above the air coming from the hair dryer. It floats! Try it with two, or even three, ping pong balls. Gravity pushes the ball down, while the column of air from the dryer pushes up. The airflow from the dryer creates an area of lower pressure. The higher air pressure surrounding the column of moving air pushes in and keeps the ball from moving sideways. These opposing forces keep the ball gently bouncing around in the air.
For this experiment with magnetism, each person needs a plastic or glass bowl, a horseshoe or pole magnet, two sewing needles and two 1-inch square pieces of flat cork. Fill the bowl about ¾ full of water. Float the two cork pieces in the water. Rub the positive end of the magnet about 30 times across the eye of both needles. Lay one needle on top of each piece of cork. Let the needles float side-by-side. Now try putting the needles with both of the eyes next to each other. Hold the horseshoe or bar magnet over a needle, but not so close that it will pick up the needle. Opposite poles of a magnet pull each other together. The same poles repel each other.