- Forces and Motion
Humans are not physically designed to fly. We cannot create enough lift to overcome the force of gravity (or our weight). The Earth tries to pull everything down towards its centre. This pull is called the force of gravity.
It's not only wings that allow birds to fly. Their light frame and hollow bones make it easier to counteract gravity. Air sacs inside their bodies make birds lighter, which enables smoother motion through air. The shape of their body helps reduce air resistance when flying, and their muscles are extremely powerful compared to their body. Their lungs are also designed so that when birds breathe they take in a lot of oxygen, which is needed to keep the muscles working over long periods of time. Why are birds' wings covered in feathers? They catch the air and force it downward when they flap. This creates lift and pushes birds up in the sky.