Why do planes fly? Gravity pulls them down. Air resistance, called drag, slows down the plane. What holds them up is lift.

 

Bernoulli’s principle is that moving air has smaller pressure than stationary air. Open a window in a moving car, and you will notice that it is harder to breathe. This is because the air pressure on your face is lower due to the moving air.

 

The wings of a plane are flat on the bottom, curved on top. The air that flows on top has to travel faster than the air on the bottom as it has a greater distance to go. Therefore, the air pressure on the top is smaller. This is lift.