WE CAN NOT SEE AIR, BUT it is not just empty space .Air is a mixture of many gases.Air exerts pressure on us,but does not crush us .In principle ,we are living on the floor of a kilometer -thick ocean of air known as the air cover or the atmosphere of the Earth.Since ,air is a matter ,it can also carry things ;leaves, in autumn ,birds,aircraft,hot air balloons,and many more things .However ,all objects need propulsion to lift from the ground-birds beat their wings, Aircraft depends on propellers or jet engines. FLYING OF AIRCRAFT - Air crafts need a combination of procedures to fly in the air .They need a propulsion system- a propeller or jet engine .They also need a lift , which comes from wings .While flying , the forward thrust causes the air to flow at great speeds along the wings