Make two ping-pong balls float in the airflow of a hairdryer simultaneously, without hitting each other. The hairdryer produces a high-velocity stream of air with low pressure. The surrounding air is at a higher pressure which keeps the ball inside the stream. When the upward force of the air equals the weight of the ping-pong ball, the ball is said to be in “equilibrium.” The theory at work here is Bernoulli’s principle. This is an equation linking air pressure, velocity, and density with particle weight.
Switch on your hairdryer, making sure it is on the cool setting.
Hold it with the nozzle pointing upwards.
Place one of the ping-pong balls into the stream of air.
Try and place another ball into the same stream of air – on top of the first ball.