In everyday life it is rare for an object to be acted upon by no forces or a single force. It is much more likely that it will experience several forces. These forces may be balanced or unbalanced.
If the two tug of war teams in figure pull with the same force, the forces are balanced and there is no movement. (Figure 1)
If one of the teams pulls with a force which is greater than that of the opposition, the forces are unbalanced and there is movement. (Figure 2)
The ship above is floating in water and is stationary. There are several forces acting upon it, so these forces must be balanced.
Gravitational forces, i.e. the weight of the ship, are pulling it downwards but a second force called the up thrust from the water is pushing upwards. (Figure 3)
If too much cargo is loaded onto the ship, the weight may become larger than the up thrust and the ship may sink.
An object placed on a table also experiences balanced forces. (Figure 4)
If an object is moving and balanced forces are applied to it, the object will continue to move in the same direction and at the same speed. The aero plane below is experiencing four forces. Its weight, a lifting force from its wings, thrust from its engines driving it forwards and drag from the air trying to resist the forward motion. (Figure 5)
If the lift and weight forces are balanced, there is no vertical motion. The aero plane stays at the same height.
If the thrust and drag forces are balanced, the aero plane will travel at a constant speed in a straight line.
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