Show that air exerts pressure.
Air is made up of molecules of different gases. The particles in air are continuously moving in all direction and collides with each other as well as with the walls of the container. The force exerted by air particles pushing in all directions is known as air pressure. As the particles in air increases, more particles will collide with the walls resulting in increased pressure.
The pressure exerted by air molecules on the Earth’s surface is called as atmospheric pressure. As the atmospheric pressure is due to weight of the air particles above, it is high at the sea level. When you ascend a mountain, the amount of air molecules per unit area decreases. As a result, atmospheric pressure is low compared to sea level. As the air pressure decreases, the amount of oxygen available also decreases. Hence, mountaineers carry oxygen cylinders when climbing very high peaks.
An instrument used to measure atmospheric pressure is called a barometer.
It should be noted that the air always flows from a place with high pressure to a place with low pressure. This flow of air caused by variation in air pressure is called as wind. The speed of the wind mainly depends on the difference in air pressure between the two regions. Strong winds can be so destructive that they can blow away roofs, uproot trees, sink boats or torn down power lines.
It is the air pressure that makes the birds fly. Birds and aeroplanes have a unique wing shape that allows air to flow more quickly over the top of the wing. The pressure of the air lowers as it moves faster. As a result, the pressure on the top of the wing is lower than that on the bottom. The difference in pressure creates a force on the wing pushing them up. The force that helps the bird to rise upward is referred to as lift.