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Unbalanced forces

When two forces acting on an object are not equal in size, we say that they are unbalanced forces.

If the forces on an object are unbalanced this is what happens:

  • an object that is not moving starts to move

  • an object that is moving changes speed or direction

There is a force of 100N behind a truck and a force of 60N in front of it. The force from behind the truck is greater than the force in front, so the truck speeds up in a forwards direction

Unbalanced forces make the truck speed up.

Resultant forces

The size of the overall force acting on an object is called the resultant force. If the forces are balanced, this is zero. In the example above, the resultant force is the difference between the two forces, which is 100 - 60 = 40 N.


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