Force

1. FORCE
A force is a push or a pull.
A force can cause an object to:
• speed up
• slow down
• change direction
• change shape
Force is measured in
Newtons (N).
Force is measured with a
Newton meter.
Types of force
Contact forces
Two bodies touch when their repulsive molecular forces (due to
electrons) equal the force that is trying to bring them together.
Friction
(also air resistance)
When two bodies are in contact their attractive molecular forces
(due to electrons and protons) try to prevent their common
surfaces moving relative to each other.
Tension
The force exerted by a body when it is stretched. It is due to
attractive molecular forces.
Non contact forces
Electrostatic
Attractive and repulsive forces due to bodies being charged.
Gravitational
The force exerted on a body due to its mass.

2. EFFECTS OF FORCE
• Make a stationary object start moving or increase the
speed of a moving object.
• Slow down or stop an moving object.
• Change the direction of a moving object.
• Distort/change the shape of an object.
Resultant force
A number of forces acting on a body may be replaced by
a single force which has the same effect on the body as
the original forces all acting together.
This overall force is called resultant force.
In the example opposite, 5N is the resultant force of the
3N and 2N forces.
3N
2N
5N

3. MASS AND WEIGHT
Mass is the amount of matter in an object.
Mass is measured in kilograms.
The mass of an object is the same on the Moon as on the
Earth.
Weight is the force of gravity on an object.
Weight is measured in newtons.
The weight of an object on the Moon is about one sixth that
on the Earth
A newtonmeter is used to determine the weight of the parcel
.

4. Gravitational field strength is a measure of how strong gravity is at a particular
place.
It is measured in newtons per kilogram (N/kg).
Calculating weight
weight = mass × gravitational field strength
weight is measured in N
mass is measured in kg
gravitational field strength is measured in N/kg
On the Earth’s surface a mass of 1kg
has a weight of 10N.
Scalar and vector quantities
A scalar quantity has size but no direction Eg:mass, area and density
A vector quantity has direction as well as size Eg: force, velocity, displacement and
acceleration
GRAVITATIONAL FIELD STRENGTH