1. How do you know there is air?
Lesson 2

2. Lesson vocabulary Air: the mixture of gases that surrounds Earth.
Equilibrium: a condition in which opposing forces exactly balance, or equal, each other.

3. Lesson vocabulary
Force: a push or pull that makes an object move, or change speed or direction, if it is already moving.
Gravity: the force that attracks things toward the centre of a large object.

4. Lesson vocabulary
Mass: the amount of of matter an object is made up of.
Pressure: a force per unit area.

5. Lesson vocabulary
Property: a quality or power that belongs specially to somthing (e.g., air exerts pressure)
Weight: the force that gravity exerts on an object’s mass (e.g., 100 kg is the force that Earth’s gravity exerts on Bob’s mass)

6. How do we know there is air?
Different experiments can be done to indicate (show) the presence of air. The presence of air can be seen by investigating its properties.

7. Properties of Air air exerts pressure 1. Pressure air takes up space
air has mass
3. Mass