Science Projects And Inventions

YOU  NEED:

• A hair dryer
• Two Ping-Pong balls

Place a hair dryer in such a way on the floor that the hot air is turned towards the ceiling. Now if you put two Ping-Pong balls in the blast of air, they two will hang in the air stream, as is shown in the illustration opposite. Pick up the ball which is higher. Hold it high, and let go into the air stream. The two balls will play hokey and change places even as they remain hanging.

HOW DOES IT WORK?

The two balls remains suspended in the air stream because water or air travelling at a high speed has lesser pressure than the water or air surrounding it. The hair dryer blast creates a column of fast moving air. The Ping-Pong balls floats because, as rushing air keeps them suspended, the still air surrounding the air  Column exerts more pressure keeping them in place. If you tip the hair dryer, the balls will remain in the low — pressure column of air shored up by high pressure surrounding them! Suppose you pick up the ball on top and drop it, the downward force of gravity will be greater than the upward thrust of air—at least to start with. The ball that is dropped falls through the column forcing its way around the floating ball. The upward rush of air is strong enough to neutralize the force of gravity. The dropped ball stops falling. Interestingly you would notice that the balls have in the meanwhile changed places!