Answer:
Unbalanced forces
When two forces acting on an object are not equal in size, we say that they are unbalanced forces. The overall force acting on the object is called the resultant force. If the forces are balanced, the resultant force is zero.
If the forces on an object are unbalanced, this is what happens:
a stationary object starts to move in the direction of the resultant force
a moving object changes speed and/or direction in the direction of the resultant force
In the example below, the resultant force is the difference between the two forces:
100 – 60 = 40 N (to the right)
Using moments
A see-saw will balance if the moments on each side of the pivot are equal. This is why you might have to adjust your position on a see-saw if you are a different weight from the person on the other end.
If a nut is difficult to undo with a short spanner, a longer spanner will help. This is because there will be a bigger moment on the nut, when the same force is applied further from the pivot.
Using the same principle you can increase the moment applied by a lever or a crowbar, and this can help you move heavy objects more easily.