1. FORCES 2 : WEIGHT vs MASS
By the end of this presentation, you should be able to :
Explain the difference between weight and mass?
Describe the difference between the weight of an object on the earth, compared to the same object on the moon (or on another planet), or in outer space.
Calculate the weight of an object if given its mass and the gravitational field strength.

2. What is gravity?
Gravity is a natural force field that exists around ALL objects.
Yes, you have your own gravitational field around you! The strength of this field is controlled by the mass of the object. The heavier it is, the stronger the field.
Gravity is always attractive, and tries to pull you towards the centre of the Earth, wherever you are standing.

3. More about the moon and planets in our Solar System
Some more facts about gravity
The closer you are to the planet, the stronger the gravitational pull.
The Moon’s gravitational field is 6 times weaker than the Earth’s.
More about the moon and planets in our Solar System

4. The strength of gravitational fields in different places
The gravitational field strength on the Earth is 10N/kg. This means a 2kg bag of flour on your foot, will exert a 20N force on your foot. This is its WEIGHT.
The table shows how the gravitational fields of the other planets compare to that of the Earth.
Go to ZoomSchool

5. Mass v.s. Weight Your mass is determined by how
much matter or atoms make up
your body. It is measured in
kilograms (kg). This will not
change with location i.e. where
you are in the Solar System, but
it might change…
if you go on a food binge!
Your WEIGHT depends on how much you are being pulled by the planet. So it depends on your MASS and the GRAVITY on the planet.
We can write weight = mass x gravitational field strength
Weight is a force so is measured in newtons

6. Changing mass to weight (using gravity)
Remember the equation Weight = Mass x Gravity
Put the quantities into a triangle for easy manipulation
The astronaut has
a mass of 60kg.
On the moon, g=1.7N/kg
On Earth, g=10N/kg W
m x g
What is his weight on Earth?
W = 60 x 10 = 600N
2. What is his weight on the Moon?
W = 60 x 1.7 = 102N