• Force

Force can be defined as a push or a pull that changes or tends to change the state of rest or uniform motion of an object or changes the direction or shape of an object. We can say that it is an influencing agency which tends to move a stationary body or which tends to stop a moving body or which tends to change the velocity (speed or and direction) of a moving body or which tends to change the shape/ size of a body. Force causes objects to accelerate or add to their overall pressure. In simple terms, force is a push or pull acting upon an object as a result of its interaction with another object. Example, to open a door, either we push or pull it. A drawer is pulled to open and pushed to close.

Effect of Force

(i) Force can make a stationary body in object. For example, a football can be set to move by kicking it, i.e., by applying a force.

(ii) Force can stop a moving body. For example, by applying brakes, a running cycle or a running vehicle can be stopped.

(iii) Force can change the direction of a moving object. For example, by applying force, i.e., by moving handle, the direction of a running bicycle can be changed. Similarly by moving steering, the direction of a running vehicle is changed.

(iv) Force can change the speed of a moving body. By accelerating, the speed of a running vehicle can be increased or by applying brakes the speed of a running vehicle can be decreased.

(v) Force can change the shape and size of an object. For example, by hammering, a block of metal can be turned into a thin sheet. By hammering, a stone can be broken into pieces.

Unit of Measurement

Force is measured in ‘Newton’ (N). Its S.I. unit is obtained from the basic formula, F = m × a, where, ‘m’ stands for the mass in kilograms and ‘a’ stands for acceleration in m/sec2. Thus, S.I. unit of force is kgm/s2.

Force is a Vector Quantity

To define the force acting upon an object completely it not only requires the magnitude but also information regarding the direction of the force. Thus, 5 N is not a full description of the force acting upon an object. In contrast, 5 N upward is a complete description of the force acting upon an object; both the magnitude (5 N) and the direction (upward) are given. Direction of any vector quantity is represented by drawing an arrow in given direction. The size of the arrow implies the magnitude of the force and the direction of the arrow reveals the direction that the force is acting.

Types of Forces:

There are various types of forces but here we will discuss following two -

(A) Balanced Forces

If the resultant of applied forces is equal to zero, it is called balanced forces. Example, in the tug of war if both the team apply similar magnitude of forces in opposite directions, rope does not move in either side. This happens because of balanced forces in which resultant of applied force become zero.

Balanced forces do not cause any change of state of an object. Balanced forces are equal in magnitude and opposite in direction. Balanced forces can change the shape and size of an object. For example, when forces are applied from both sides over a balloon, the size and shape of balloon is changed.

(B) Unbalanced Forces

If the resultant of applied forces are greater than zero, the forces are called unbalanced forces. An object in rest can be moved because of applying balanced forces. Unbalanced forces can do the following:

1. Move a stationary object
2. Increase the speed of a moving object
3. Decrease the speed of a moving object
4. Stop a moving object
5. Change the shape and size of an object