Chapter 4 – Birds and Mammals Lesson 2 – The Physics of Bird Flight
Staying in the Air • All objects on land are surrounded by an invisible ocean of air. • Air is a mixture of gas molecules that exert pressure on the objects they surround.
Movement and Air Pressure • Air does not have to be inside a balloon to exert pressure. • Moving air exerts pressure, too.
Air Movement Around a Wing • The difference in pressure above and below the wings as a bird moves through the air produces an upward force that causes the bird to rise. • This upwards force is called lift. • The wings of birds allows air to flow smoothly over and under it.
Birds in Flight • Three types of bird flight are flapping, soaring and gliding, and diving. • Before a bird can use lift to fly, it must have some way of getting off the ground. • To get into the air the bird must move forward to make air move over its wings.
Flapping • Once in flight, all birds continue to flap their wings at least part of the time. • To flap, a bird must sharply pull down its wings as it did when it pushed off the ground.
Soaring and Gliding • Unlike flapping, soaring and gliding flight involve little wing movement. • Birds soar and glide with their wings extended. • Sometimes birds fly using a combination of soaring and gliding. • They “take the elevator up” by flying into a current of warm, rising air. The birds stretch their wings out and circle round and round, moving upward within the current of rising air. As the warm air rises, it starts to cool. Finally the air stops rising, and at this point the bird begins gliding downward until it reaches another “up elevator” of rising air.
Diving • A type of flight that doesn’t use lift is diving. Birds that hunt their prey from the sky may use diving flight. • Some hawks and falcons dive from high in the sky towards their prey. • Peregrine falcons can clock speeds up to 300 kilometers per hour while diving for pigeons or other prey.