Have you ever been on an airplane? If you have, you may have wondered how they can fly. Airplanes are big. They are heavy. How can they fly through the air like birds?
A bird or airplane flying in the air has four different forces acting on it. There is a force that pushes up. There is a force that pushes down. There is a force that pushes forward. There is a force that pushes backward. A bird flying through the air can change the way that it moves to change the way that the forces act on it. People can make an airplane fly by controlling the way that forces act on it.
Gravity is the name of the force that pushes things down toward the ground. The force is greater for heavier objects than it is for lighter objects. That means that airplanes need to be light in order to fly. Airplanes are made with light materials. They use lightweight aluminum instead of steel. They use plastic instead of glass. Every little bit helps to keep the airplane as light as possible.