GCSE Resultant Forces

Resultant Forces

A resultant force is a single force that takes account of all the forces acting on an object.

In the diagram above, the car has a forward driving force of 500N, drag forces of 200N.

So, the resultant force is 500N-200N = 300N to the right.

This example can also be represented using a box diagram as shown below:

Value of the Resultant Forces

Resultant force of 0N

If the resultant force is 0N, then this means that the forces acting on the object are balanced as shown below.

In this case there is a 500N downwards force due to weight and a 500N upwards force. These forces are equal in size, but opposite in direction. Therefore, the resultant force is 0N and the forces acting on the object are balanced.

500N-500N = 0N.

Resultant force is not 0N.

Sometimes the forces on an object do not cancel out completely, so there is an overall resultant force. This means that the forces are unbalanced.

In this case the tennis ball has a forward force of 100N, but drag force of 20N. So, the resultant force is 80N to the right, or in forwards direction.

100N-20N = 80N

Practice Questions

1. Use the following box diagrams to calculate the overall resultant force, in addition state the direction of the resultant force.

2.A cardboard box is placed onto the floor. Whe box has a weight of 50N and the floor provides a reaction force that is equal in size, but opposite in direction. Draw a box diagram to represent this.

3. An airplane has a engine thrust force of 5kN and air resistance of 2kN. Calculate the resultant force on the airplane.