Hair-drier and ball

The ball placed in the stream of hot air from the drier hovers freely. The ball vibrates sideways but does not fall down. This means that, according to Newton's laws of dynamics, the forces on the ball counterbalance each other (gravity is counterbalanced aerodynamic lift of the hot air). It is somehow similar to a uniform fall of a parachute jumper, the only difference being that the air flows and the ball hovers in place.

Why is the point of equilibrium situated in the middle of the air stream where there is the greatest velocity and the ball should theoretically be blown away? This phenomenon is explained by so called Bernoulli's principle. The principle says that where the velocity of flow is greater, the pressure is smaller. The smaller pressure in the centre of the current sucks the ball in.

The same principle explains why planes fly in the air.