Physics in Flying Kite

The Bernoulli Theorem explains why the kite has lift. The kite creates an obstacle to the normal airflow that causes the air to change direction and speed.

If you hold the kite out flat to the wind like a wing, beneath the kite the wind is slowed down and therefore the pressure of the wind increases to compensate. Above the kite, the air is not slowed down and sometimes is sped up so that pressure either stays the same or decreases. The pressure difference between the kite's bottom and top surfaces causes the lift force.