# Force

Any action which causes pull or push on a body is called force. Forces are used in our everyday actions like pushing, pulling, lifting stretching, twisting and pressing.

Force produces any of the following effects on the body. A force can

• Move a stationary body
• Change the state of rest or motion
• Stop a moving body
• Change (increase or decrease) the speed of a body.
• Force Change the shape and size of a body.
• Change the direction of the motion of a moving body

Force is a vector quantity, its SI unit is Newton and the CGS unit is dyne.

1 newton = 1 kg-ms-2

1 newton = 105 dyne

e.g., a force is used when we kick a football, we lift a box from the floor, we stretch a rubber band, etc.

## Fundamental or basic Force in Nature

### Gravitational Forces

Every object in this universe attracts each other, this force of attraction is called gravitational force. It is the weakest force among all existing forces and is negligible for all lighter and smaller bodies but becomes significant and considerable in all celestial bodies.

### Weak nuclear Forces

These forces were discovered during the study of the phenomenon of β-decay, in radioactivity. These are the forces of interaction between elementary particles of short lifetimes. The weak nuclear forces are 1025 times stronger than gravitational forces.

### Electromagnetic Forces

The electromagnetic forces are the forces between charged particles. When the charges are at rest, the forces are called electrostatic forces. The forces between unlike charges are attractive and the forces between like charges are repulsive. These forces are governed by Coulomb’s law.

Matter consists of elementary particles like electrons and protons. The electrons and protons are charges. Electromagnetic forces are much stronger than the gravitational force. It dominates all phenomena on atomic and molecular scales.

### Strong Nuclear Forces

The forces that bind the neutrons and protons together in a nucleus are called the strong nuclear forces. These forces act between two protons or two neutrons or a proton and a neutron, but only if the particles are very close together. These are strongest forces in nature. These are 1038 times stronger than gravitational forces, 102 times stronger than electrostatic forces and 1013 times stronger than the weak forces.

## Types of Force

### Balanced Forces

When the net effect produced by a number of forces acting on a body is zero, then the forces are said to be balanced forces. Balanced forces can only bring a change in the shape of the body e.g., If the block is pulled from both the sides with equal forces, the block will not move, such forces are called balanced forces.

### Unbalanced Forces

When the net effect produced by a number of forces on a body is non-zero, then the forces are said to be unbalanced forces.

• An object moves with a uniform velocity when the force acting on the object are balanced and there is no net external force on it.
• If an unbalanced force is applied to the object, there will be a change either in its speed or in the direction of its motion. Thus, to accelerate the motion of an object, an unbalanced force is required.