A worksheet produced by the Native Access to Engineering Programme Concordia University, Montreal. In order to understand how an airplane flies, you have to look at the forces which act on the plane. There are two forces which work to slow a plane down and keep it on the ground. These are drag and weight. Drag is a backwards force caused by air flowing over the body of the plane.
Weight is a downwards force caused by the Earth's gravity acting on the mass of the plane.
In order to get into the air you need to create forces which are pushing forward and up more than drag and weight are pulling backwards and down. These forces are thrust and lift. Thrust is a forward force created by engines or propellers. Lift is an upwards force caused by the effect of air moving over the plane's wings. If you have the same amount of pressure on every side of an object, it won't move.