Lesson 2 Introduction
Look at the glass in this picture. What is inside the glass? Is it empty?
Of course not! The glass is full of air! Since we cannot see it, we are going to have to think of some creative ways to prove that the air is really there.
Air may be invisible, but you are probably starting to realize how powerful air is. We rely on air to breathe. Air is used even in brakes to stop large moving trucks and trains. Air is the reason we are able to fly. More details on that will come later, but first, look at some properties of air.
Properties of air:
1. Air has mass and volume.
Remember that air is a gas, which means it is made of many tiny, tiny particles. These tiny particles may be invisible, but they are present and have mass. The particles weigh something, and they take up space (volume). Although they may be extremely light because they are so small, there is a way for you to show how the gas particles in the air have mass (or weight).
2. Air exerts pressure
These tiny particles that make up air are bumping constantly into things as they move. When this happens, these particles are exerting “pressure”. Air exerts pressure in all directions.
When you are underwater, you can feel the pressure of the water particles pushing on you. Air does the same thing, but we do not feel it because we are so used it. If you climb a high mountain you will discover that there are less air particles than at lower elevations. For this reason, the air pressure at the top of the mountain is lower than the air pressure at sea level.
On the next page we will explore these properties further!