Force:Force is an external agency that changes or tends to change the state of body, rate of motion direction of motion and shape and size of object. A force is the push and pulls in the object.

From this we can conclude that the force is an external agency that changes or tends to change the state of rest or uniform motion of any body when an external force is applied on it.

Effect of force:

Force can produce following effects on an object.

1. It can change the state of object. Force can bring an object into rest from motion and in motion from rest.
2. It can change rate of motion. Force can accelerate and decelerate a moving body.
3. It can change the direction of a moving object.
4. It can change the structure and size of an object.

Measurement of force:

Force is measured by spring balance and its SI unit is Newton and cgs unit is dynes.

1 Newton = (1kg x 1m/1S²)

= (1000g x 100cm) / (1S²)

= 10⁵g cm/s²

1 Newton = 10^{5 dynes}

Vector and scalar quantity:

All physical quantities are classified into two groups; the vector quantity and the scalar quantity. A physical quantity having both magnitude and direction is a vector quantity. Vector quantity is written with arrow head or is simply represented by block letter. Force, displacement, velocity, acceleration are some examples of vector quantity.

A physical quantity having magnitude only is called scalar quantity or simply scalar. Mass, density, distance, time, temperature, etc. are some examples of scalar quantity.

Difference between vector and scalar: