Question

Which force act's on a kite to make it fly??

Answer 1

They are gravity, lift, thrust, and drag.

Gravity pulls everything towards the centre of the earth. Anything on the ground can't get pulled down any further than that, but things in the air can get pulled down to ground level. The heavier a kite is the harder it will be to fly. Kites are generally made from lightweight materials so that they will fly easily.

If gravity is a force that pulls everything towards the centre of the earth, why don't kites get pulled down to earth? The force that stops a kite from falling down is called lift. Lift is the force pushing the kite away from the surface of the earth. It is produced by air moving over the top of the kite at a faster speed than the air that is moving over the bottom of the kite. Daniel Bernoulli, a scientist in the eighteenth century, discovered that the pressure of air becomes lower when it is moving. The faster the air is moving the lower the pressure becomes. A kite is shaped so that air will be slowed down if it is travelling under the lower surface of a kite and will speed up if it is travelling over the upper surface of the kite.



The faster the air moves over the upper surface of the kite the lower the pressure of that air becomes. As the air pressure above the kite becomes lower, the air pressure below the kite pushes the kite up in order to equalize the pressures above and below the wing. The greater the difference between the low pressure above the wing and the higher pressure below the wing, the greater is the amount of lift produced. In order for all this to happen, air needs to be moving over the kite. So what makes the air flow over the kite?

When we fly kites we use a string to hold on to the kite, and to prevent it from being blown away by the wind. Birds move through the air by flapping their wings, while powered aircraft use an engine to push the air towards the back of the plane fast enough to make the aeroplane move forward. The force that makes something move forward through the air is called thrust. Birds use muscle power to develop thrust, and except for gliders, aeroplanes use motors. A kite cannot produce its own thrust, and instead must rely on being held in place while the wind moves past it. So the thrust that acts on a kite is produced because the kite is being held in one place by its string while the wind flows around the kite. If there was no wind a kite would only fly if the person holding the kite string started running, making their own wind as air started flowing around the kite.



What stops a kite from flying straight over your head and into the ground on the other side? As the air flows over the surfaces of a kite the wind gets held back a little bit by the roughness of the fabric and the sticks. This friction is called drag.