Forces are pushes or pulls. They are measured in newtons (N). Forces may vary in size and act in different directions.

If a number of different forces act on an object they can be replaced by a single force called the resultant force.

If the resultant force acting on a stationary object is zero the object won't move. If it is not zero the object will move in the direction of the resultant force.

The change of an object depends on the size of the resultant force (bigger force greater acceleration) and the mass of the object (bigger mass smaller acceleration).

The speed of an object is a measure of how fast it is moving. The speed of something can be worked out if you know the distance it travels and the time it took to do so.

Speed can also be determined from the slope or gradient of a distance-time graph. The steeper the slope the greater the speed.

The acceleration of an object is the rate of which its velocity changes. It measures how quickly an object speeds up or slows down. To calculate it you need to know the change in velocity and the time taken for the change.

Deceleration is a negative acceleration. It describes an object that is slowing down. It is calculated using the same equation as for acceleration.

Friction is a force that occurs when an object moves through a medium (like air or water) or when surfaces slide past each other. Friction works against the object in the opposite direction to which it is moving, its a resistive force.

The overall stopping distance is increased if: the vehicle is travelling at a greater speed, there are weather conditions like ice, the driver is tired or under the influence of drugs, the driver is using their mobile or the vehicle is in a poor condition.

To calculate the weight of an object the following equation is used: W = m x g.
W= newtons.
m= mass in kg.
g= gravitational field strength in N/kg.

A force acting on an object may cause the object to change its shape. A force applied to an object when it is able to return to its original shape when the force is removed is said to be elastic.

The amount of work done, force and distance are related by the equation: W = F x d.
W= work done in J.
F= force applied in N.
d= distance moved in the forces direction in m.

Gravitational potential energy can be calculated using the following equation: Ep = m x g x h.
Ep= the change in GPA in J.
m= mass in kg.
g= G field strength in N/kg.
h= height in m.

Momentum can be calculated using this formula: p = m x v.
p= momentum in kg m/s.
m= mass in kg.
v= velocity in m/s.