2007-09-01 23:33:41 · 8 answers · asked by dark knight 1 in Science & Mathematics ➔ Physics
because they flap their wings. feathers have a very special structure that let the air pass easily in one direction (up->down) but not in the other.
They are also very light because they have no fat, thin bones and a lot of other little natural optimisations.
2007-09-01 23:39:24 · answer #1 · answered by paulatz2 2 · 0⤊ 1⤋
Birds fly in the same way any airplane does.
It all boils down to Bernoulli principle. Take an airplane wing as an example. The wing of an airplane has two surfaces. The bottom surface is rather flat while the upper surface is rounded. As the wing moves relative to the air, the air passing close to the upper surface has to travel higher distance that the air traveling close to the lower surface. Despite this difference in distances to be traveled, the two portions of air (the one on top and the one below the wing) that separated at the leading edge of the wing meet at the end of the wing at the same time, which means that the air traveling close to the upper surface had to move faster than the air traveling close to the lower surface. This difference in air velocities causes a difference in pressure, being lower pressure when the speed is higher and for this reason a differential pressure is created across the lower and upper surfaces of the wing. Higher pressure is at the bottom and lower pressure is on the top. If you take this difference in pressure pointing upwards and multiply by the surface of the entire wing, then you will have a force (lift) pushing the airplane upwards. This is the force acting against the force of gravity. Remember that Pressure = Force / Area. The higher the wing surface, then the higher the lift. Also, as you can see, wings need air to fly through. If there is no air, say in vacuum, then the Bernoulli principle would not work and airplanes and birds could not fly in the way we know they do today.
2007-09-02 06:57:39 · answer #2 · answered by timeton 3 · 0⤊ 0⤋
A Bird when flying in the air is subject to
gravity pushing him down toward the Gravitational mass of the earth.
However due to the birds movement and the structure of its wings causes the bird to get a upward push against the Push of gravity.
The upward push on the wings of the Bird is from the mass of the air resisting Gravity. The balancing to the gravity down ward push and upward push of the air mass causes the bird to float in the air.
The airplane wings obey the same rules as the birds wings.
The rules are ;Bernoulli's principle of fluid dynamics and Newton's 3rd Law of motion.
2007-09-02 08:32:43 · answer #3 · answered by goring 6 · 0⤊ 0⤋
The movement of their wings act against gravity. The same effect as that of the propellor of a helicopter. The downward push of the wings lift their body upwards. If they close their wings they fall. But if they keep open the wings but not pushing down they will go on gliding.
2007-09-02 09:49:24 · answer #4 · answered by Joymash 6 · 0⤊ 1⤋
Bernoulli principle makes the bird fly. They are not exempt from gravity but overcome this through lift and move forward through thrust. Tricky animals if you ask me.
2007-09-02 15:27:01 · answer #5 · answered by tk 4 · 0⤊ 0⤋
Firstly, they have got wings to fly unlike us.
Secondly, they have hollow bones which makes them light in weight for a flight in the air!
Hope this helped :)
Thank you.
2007-09-02 08:49:09 · answer #6 · answered by ♥Hermione answers♥ 3 · 0⤊ 1⤋
They create lift and thrust by flapping their wings.
2007-09-05 23:03:32 · answer #7 · answered by johnandeileen2000 7 · 0⤊ 0⤋
If they don't flap, they fall down, go boom.
2007-09-02 06:52:08 · answer #8 · answered by Anonymous · 0⤊ 1⤋