SI unit kilogram (kg)

The mass of a body resists a change in the state of rest or motion of the body.

The tendency of a body to resist a change in the state of rest or motion is known as Inertia.

The greater the mass, the more resistance there will be to the change in state (or greater in inertia).

E.g.: compare to stop a metal ball & a plastic ball at the same size.

Gravitational field

A region in which a mass experience a force due to gravitational attraction.

E.g. : When you release an object from a distance above the ground , the object will drop to the ground.

*The earth has it’s own gravitational field, so does the moon and any other large planets.

Gravitational field strength, g, in defined as the gravitational force per unit mass.

SI unit: NKg-1

SI unit: m/s2

(As the GFS is infect the gravitational acceleration)

Weight

_ The product of mass and gravitational field strength

W=mg

SI unit: Newton (N)

Note that different substances have different masses even though they have the same volume. This is because different substances have different densities. A substance with a high density is said to be denser, whereas a substance with a low density is said to be less dense. This is the reason why oil (that is less dense than water) floats on water. On the other hand, honey, which is denser than water. The table on the next page shows the densities of some substances.