(It is now easy to understand that we need to know both the magnitude of force, and the direction in which it acts, to completely specify it. When we change either the direction, or the magnitude, or both (magnitude and direction) of the applied force, its effect changes.)
Do You Know?
The force need not always act in the direction of motion. Depending upon the situation, force may act at any angle to the direction of motion. A force, acting perpendicular to the direction of motion, does not cause any change in speed but can still cause a change in direction.
Balanced and Unbalanced Forces
From our experience we know that sometimes more than one force can act on an object. The effect of all these forces on the object, would be due to the net force acting on it.
It is the net unbalanced force, acting on an object, that changes its speed or direction of motion, or both. When the two forces, acting on an object, are different, the object undergoes a change in its state of rest or motion. The change caused depends on the net force acting on it. We call a pair of different forces as unbalanced forces.
1. Unbalanced forces, acting in the same direction, combine by addition.
2. Unbalanced forces, acting in mutually opposite directions, combine by subtraction. The net force is equal to the difference between the two forces and is exerted in the direction of the larger force.
The resultant (net) of unbalanced forces is always non-zero) For example, in a game of tug of war, the weaker team always gets pulled towards the stronger team.
The figure shows a block of wood, lying on a table, that has been tied to two springs. If we pull the block from both sides, with the same force, the block remains stationary. The forces are equal and opposite. The net force is zero. Similarly, in a game of tug of war, when both the teams pull the rope, with equal and opposite forces, the rope remains stationary The net force again is zero. We call such a pair of forces as balanced forces.)
Now, try to squeeze a rubber ball between your palms by applying nearly same force from both sides. As the forces applied are equal and opposite, net force is almost zero. It does not move the ball, but can deform it.
We thus conclude that–
- equal and opposite forces (balanced forces) do not change the state of rest or motion of an object. They may, however, cause a change in the size and/or shape of the object.
- unequal (unbalanced) forces may lead to (i) change in state of rest or motion as well as (ii) change in size and/or shape of an object.