An airplane can weigh more than 80 elephants, and it still flies. The secret is in the shape of its wings.

A wing is curved on top and flatter on the bottom. When the plane races forward, air rushing over the wing has to move in a special way: the wing pushes air down, and the air pushes the wing up. Scientists call that push lift. The faster the plane goes, the stronger the lift — which is why planes speed down the runway before takeoff.

That is also why airplanes have such big engines. The engines do not lift the plane — they push it forward. The wings do the lifting, as long as the plane keeps moving fast.

Try this: stick your hand out of a car window (ask first, and only a little bit). Tilt your hand up slightly and feel the air push it upward. Your hand just became a wing.