Mass and weight
Mass is a measure of how much matter there is in an object, while weight is a measure of the size of the pull of gravity on the object.
Gravitational field strength
On earth, the downward force of gravity on a 1 kg mass is 10 N.
This is called the gravitational field strength (g).
Gravitational field strength g = 10 N/kg
The relationship between the weight of an object in N, its mass in kg and the gravitational field strength N/kg is given by the equation:
weight W in N = mass m x gravitational field strength g
W = mg
W = weight in N
m = mass in kg
g = gravitational field strength in N/kg
g = 10 N/kg
A mass of 1 kg has a weight of 10 N.
A mass of 6 kg has a weight of 60 N.
How big is a force of 1 N?
An average apple has a mass of 100 g or 0.1 kg.
The weight of the apple is:
W = mg
m = 100 g = 0.1 kg
g = gravitational field strength g = 10 N/kg
W = 0.1 kg x 10 N/kg
W = 1 N
So, a force of 1 N is the force need to lift an average sized apple off the ground.
The Wmg triangle
W = weight
m = mass
g = gravitational field strength
| W = mg | W = m x g |
| m = \(\frac{\text{W}}{\text{g}}\) | m = W ÷ g |
| g = \(\frac{\text{W}}{\text{m}}\) | g = W ÷ m |
| W = mg |
| W = m x g |
| m = \(\frac{\text{W}}{\text{g}}\) |
| m = W ÷ g |
| g = \(\frac{\text{W}}{\text{m}}\) |
| g = W ÷ m |
