Forces and movement

This lesson covers: 

  1. What forces are and how they interact with objects
  2. Key effects that forces can have
  3. Balanced and unbalanced forces

What are forces?

Forces are pushes or pulls between two interacting objects.

Diagram showing a newton meter measuring weight, with labels for tension in spring, weight, and mass.

Some key points about forces:

  • They cannot be seen directly, only their effects
  • Measured in units called newtons (N)
  • Usually act in pairs in opposite directions
  • Act in a specific direction
  • Can be measured using a newton meter
  • Forces do not require objects to touch - magnetism, gravity, and static electricity are examples of non-contact forces.

The five effects of forces

Applying a force to an object can cause five different outcomes:

  1. Speed up or start moving
  2. Slow down or stop
  3. Change direction
  4. Turn or rotate
  5. Change shape


To make an object move from rest, the applied force must overcome resisting forces like friction.

Balanced forces

Illustration of balanced forces showing an apple on a table with upward reaction force and downward weight force.
  • Balanced forces cause no acceleration.
  • For example, a book on a table has balanced downward gravitational force and upward reaction force from the table.

Unbalanced forces

Diagram showing a rocket with thrust and weight forces indicated.
  • Unbalanced forces change speed and/or direction of motion.
  • For example, a rocket experiences unbalanced forces upwards from thrust and downwards from gravity, causing vertical acceleration.