As you know, gravity is the natural force that pulls everything to the ground. For a plane to become airborne and to say in the air, its wings must create a lifting force greater than the downward pull of gravity. When a plane stands on the ground, the air pressure above and below its wing is equal. As the plane starts moving forward, air begins to flow over and under the wing. The air moving over the curved upper surface of the wing flows in a curve. As it does so, its speed increases and its presure drops. Meanwhile, the air moving under the flat bottom of the wing moves in a straight line. Its speed and pressure remain unchanged.

Air always flows from a high pressure area to a low pressure area. Therefore, the air under the wing tries to move upwards to the air above the wing. But it comes up against the wing instead. So the air cannot meet the low pressure area, and instead, its high pressure lifts the wing into the air.

The faster the aeroplane moves, the greater the lift its wings produce. As a speeding aeroplane builds up more and more lift, the force of the lift finally becomes greater than the force of gravity. The plane then takes off.

NOTE: Did you know that some aircrafts weigh less than their pilots? These are usually specialised aircrafts, such as hanggliders, microlights, pedal-powered and solar-powered planes.