Why do birds fly?

Question

Why do they?

Answer 1

Because they can. It's like when you COULD walk downtown, but the car is RIGHT there... They can walk and fly, but they get where they're going a whole lot quicker when they take flight.

Answer 2

There are two natural forces that a bird must overcome so that it can fly:

Gravity - the force that draws all objects to the ground
If you let go of an object from your hand, it falls to the ground because of gravity.
Drag - the force that slows things down
If you move your hand, palm facing forwards, through the air, this is the force you can feel on the palm or back of your hand.
The bird must generate a force, called lift, that pushes it away from the ground, and another force called thrust that pushes it forward through the air.

Intuitively, the downward flap of a wing beat should create lift, but then why doesn't the upward flap do the opposite? The answer is partly explained by how birds soar and glide.

When a bird is soaring it does not flap its wings and yet it is creating lift so as to remain aloft. This is the amazing, counter-intuitive part: lift is created not by flapping but by air flowing over the surface of the wing.

If we take a slice through a bird's wing its shape is like a teardrop, which is called an aerofoil. When an oncoming stream of air hits the leading edge of an aerofoil it splits into two air streams, one passing over the top of the aerofoil and the other underneath. The air streams below the aerofoil bunch together forming a higher pressure region whilst those above spread apart to form a lower pressure region. The difference in pressure above and below the aerofoil creates lift.

Thrust is the force required to overcome drag and drive the bird forwards. The counter-intuitive discovery that lift is created by air flow over the wing prepares us for an equally complicated explanation for how birds create thrust.

If we watch a large bird that has a slow wing beat, such as a member of the crow family, we can see that the wing is not simply flapped up and down. On the downstroke, the wing tip moves downwards and slightly forwards and on the upstroke the tip also moves backwards. This gives the impression that the bird is swimming or rowing through the air. Unfortunately, it is not quite so simple.

Towards the end of the downstroke, the air beneath the wing causes the feathers to twist into a vertical position. Each of these flight feathers is also shaped as an aerofoil. With the front facing surface of the feather corresponding to the top surface of the aerofoil, air passing over the surfaces of the twisted feather creates a forwards pushing thrust.

Answer 3

Birds originated as reptiles. It was a great advantage for them from the standpoints of mobility, food gathering, and safety to be able to fly rather than crawl.

Answer 4

not all of them! some can't fly and those who fly, fly because they have owned the godgifted wings.their bones contain air which makes them light in weight.

Answer 5

It's their protector....All animals have a defence mechanismn birds fly?!

Answer 6

because the force of the wings movement have neccesary energy to win the force of gravity

Answer 7

To get around.

Answer 8

Why do fish swim?

Answer 9

they need to see

Answer 10

because they can?