Balanced forces
If the push and the pull are the same size, then no resultant force acts on the object and the forces are said to be balanced.
Resultant force = 5000 N - 5000 N = 0. The forces are balanced.
What happens when balanced forces act on an object?
Newton’s First Law of Motion states that: a body will remain at rest or continue to move at constant speed in a straight line, unless a resultant force acts on it.
Another way of saying this is:
If the forces acting on an object are balanced,
- it stays at rest if it is already at rest, or
- it keeps moving at constant speed in a straight line if it is already moving at constant speed in a straight line.
Look again at this example:
The thrust from the engine is equal and opposite to the drag caused by air resistance and friction between the road and car tyres.
There is no resultant force as the forces add up to zero.
The car is already traveling forward at 20 m/s and so it will continue to travel forward with a speed of 20 m/s in a straight line.
Example
The upward force equals the downward force and they both act on the car.
The forces are balanced.
The car is already at rest, and so it remains at rest.
It does not move upwards or downwards.
Summary
Balanced forces have no effect on an object.
- If it is at rest, it remains at rest.
- If it is moving at constant speed in a straight line, it continues to move at the same speed in the same straight line.
