The effect of air pressure on us is significant but we do not notice it. When you consider that 300 kg of air is present in an average sized classroom that surely must have some impact on our surroundings. Air is made up of different tiny molecules. These molecules constantly collide with surfaces. The surface of your skin sustains billions of collisions every second. The molecules are so small that we hardly feel the impacts. Take a glass window for example, the number of collisions on the outside of the window equal the number of collisions on the inside. This balance prevents the glass from being smashed by the air pressure. Conduct the following demonstration where the number of collisions on the outside of the can far exceed those on the inside.

As the water is heated in the can, steam displaces all the air inside. Water molecules now totally take over the interior of the can. Explain what happens to crush the can when it is placed in the water. Use the words molecules, collisions, condensation, vacuum, air pressure.