1. Forces Types of forces Mass and weight Forces and motion Friction
Contents
Forces
Types of forces
Mass and weight
Forces and motion
Friction
Summary activities

2. Gravitational attraction
Gravity is an attractive force that exists between all masses.
The larger the mass, the greater the gravitational attraction.
The greater the distance between masses, the smaller the gravitational attraction.
The Earth has a large mass and so produces a strong gravitational force.
The Moon is kept in orbit around the Earth by the pull
of the Earth’s gravity.

3. Gravity and weight
The pull of the Earth’s gravitational force on an object is called weight.
The Moon also has a gravitational force.
Why is the weight of an object
on the Moon less than the
weight of the same object on
the Earth?
The Moon is smaller than the
Earth and so the pull of the
Moon’s gravity is weaker than
the pull of the Earth’s gravity.
This means that the weight of
the object is less on the Moon.

4. Mass and weight 1 kg What is the difference between mass and weight?
mass = 1 kg
1 kg
weight = 10 N
Mass is the amount of matter that makes up
an object.
The mass of an object is always the same, wherever it is in the Universe.
Weight is a force due to the pull of gravity on an object.
The weight of an object will vary depending on where it is in the Universe.
The units of mass are kilograms (kg).
The units of weight are newtons (N).

5. Mass and weight – true or false?