How Birds Are Like Planes Air is not just empty space. It has substance just like all things on this planet. Since air has mass, earth's gravity attracts it and gives it weight. Since air has weight, it presses on things it exerts pressure.
Birds are different from planes in that they are able to get both lift and thrust from their wings.
As a bird flaps it's wing it is not just moving the wing up and down. The wing is actually moving down and forward during the down stoke and up and forward during the upstroke. The path of the wing looks like a figure eight. The outside part of a bird's wing is just like a propeller. When a bird glides it is similar to how a glider glides.