Balanced and Unbalanced Forces

Balanced and unbalanced forces are defined as follows:

Balanced forces: two forces are balanced if their magnitude is equal and they are opposite in direction so that their sum is zero.

Unbalanced forces: two forces are unbalanced if their magnitude is different and they are not opposite in direction so that their sum is not zero.

If the forces on an object are balanced, the body does not change its motion, while if they are unbalanced, this is what happens:

• a stationary object starts to move in the direction of the net force.

• a moving object changes speed and/or direction in the direction of the net force.

A tug of war, where each team is pulling equally on the rope, is an example of how balanced and unbalanced forces work. When the forces exerted on the rope are equal in size and opposite in direction, the rope will remain stationary. However if the players on one side of the rope use more force than the other side, the forces acting on the two sides of the rope will no longer be balanced. As a result, the losing team will move in the direction of the net force, such as towards the team that won.

Figure 1: Two possible scenarios of tug of war game. In a(a), the two teams are applying the same force on the rope, therefore the forces are balanced and the rope won't move. In b(b), the team on the left is using more force. As a result, the player on the right is pulled towards the winning team, such as in the direction of the net force. In this example the net force is 300 N - 100 N = 200 N to the left.