Two forces of equal size acting in opposite directions on an object, are balanced. They fully cancel each other out so no change is caused.

Unbalanced forces do not fully cancel out.

The ‘force left over’ is called the resultant force.  Resultant forces cause changes in speed.

Balanced and unbalanced forces

Science

In the Hidden forces unit, they will build on this knowledge to learn about turning forces, forces that hold objects on a surface, and those that make some objects float.

In primary science, pupils learnt that air resistance, water resistance and friction push back against moving objects. 

Forces

The resultant force on this car is {{}} N.

Which pictures show a resultant force of 12 N? Tick as many as you think.

If the forward force is bigger than the backward force.

Which would cause an object to change speed? 

With these forces acting, the car could be stationary and remaining stationary.

With these forces acting, the car could be moving forwards at steady speed.

With these forces acting, the car could be moving forwards and getting faster.

With these forces acting, the car could be moving but will now immediately stop.

With these forces acting, the car could be moving backwards at steady speed.

The diagram only shows the forces acting on this car, not whether it is moving or not. Which of the following could be happening to this car?

It keeps moving forwards at steady speed.

It immediately starts moving backwards at steady speed.

It immediately starts moving backwards and speeding up in that direction.

This car is moving forwards. What happens next to this car, with these forces acting?

Forces make things change. A larger force will cause a bigger or __________ change.

Something is bigger on one side than the other.

Two things acting in different directions are adding up to have a bigger effect.

Two things are equal in some way but are cancelling each other out.

Which option is the best description of what it means when two things are balanced?

A person walks 9 metres straight forwards, then 4 metres straight backwards. The result of doing this is they are {{}} metres from where they started.

Forces can change an object's {{}}, direction or shape. 

there is not enough information to decide

Are the forces on this car balanced or unbalanced?

This lesson will soon be taken down.

Balanced and unbalanced forces

Lesson outcome