Four forces act on an aeroplane when its flying.

Four forces act on an aeroplane when its flying.
1) Lift: is an upward force that holds an aeroplane in the air.
2) Thrust: is the force that moves the aeroplane forward.
3) Drag: is air resistance that holds the aeroplane back.
4) Weight: is the force that pulls the aeroplane down.
The wings of an aeroplane are a a special shape, called an aerofoil. The top of the wing is straight.
Lift comes from an aeroplane's wings. Because the top of the wing is curved, air has further to go over the top than it does under the wing. This produces a lifting pressure over the wings that supports the weight of the aeroplane.
Gliders, hang gliders and birds use thermals to gain height during flight. Because they are light weight, they gain height when circling in thermals. A glider will only fly if it is moving fast enough to keep air flowing smoothly past its wings to create lift. Gliders gradually descend back to the ground unless they are flying in the air that is rising at a rate faster than the glider's normal rate of descent.
How Thermals are made:
Thermals occur when a column of warm air rises from heated parts of the ground. Air also rises when the wind meets rising ground such as hillsides, mountain ranges and coastal sand dunes.
hot air-balloon is a huge envelope, or bag, made of light material that is filled with heated air. Passengers are carried in a basket or gondola suspended underneath. Hot-air balloons rise because the air