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Equilibrium Forces

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Key Stage 3

Meaning

Equilibrium forces are a pair of equal forces acting on opposite sides of an object in opposite directions.

About Equilibrium Forces

Equilibrium forces can act to stretch or squash an object.
When an object is acted on by two equal, but opposing forces, the object is in equilibrium.
Elastic objects like springs need two opposing forces to change length. Once the forces have been applied the spring will stay at this new length until the forces are removed.
SpringForcesEquilibrium.png
The spring will stretch to a certain length and then stay the same due to two opposing forces.
If one force were bigger than the other the elastic object would accelerate rather than stretch. This is what happens when a rubber band is flicked. It begins in force equilibrium stretched by two fingers pulling in opposite directions. When one finger is removed there are no longer two opposing forces so the rubber band accelerates.

Key Stage 4

Meaning

Equilibrium forces are a pair of equal magnitude forces acting on opposite sides of an object in opposite directions.

About Equilibrium Forces

Equilibrium forces can act to stretch or squash an object.
When one object is acted on by two forces which are equal in magnitude but opposite in direction the object is in equilibrium.
Elastic objects like springs need two opposing forces to change length. Once the forces have been applied the spring will stay at this new length until the forces are removed.
Plastic objects also need two opposing forces to change length. However, while the force is applied the object will continue to stretch until the forces are removed. At that point the plastic object will remain at this new length.
SpringForcesEquilibrium.png
The spring will stretch to a certain length and then stay the same due to two opposing forces.
If one force were bigger than the other the elastic object would accelerate rather than stretch. This is what happens when a rubber band is flicked. It begins in force equilibrium stretched by two fingers pulling in opposite directions. When one finger is removed there are no longer two opposing forces so the rubber band accelerates.