Newton’s First Law of Motion

A body continues to be in its state of rest or in uniform motion along a straight line unless an external force is applied on it.

This law is also called law of inertia.

Examples

1. When a carpet or a blanket is beaten with a stick then the dust particles separate out from it.
2.  If a moving vehicle suddenly stops then the passengers inside the vehicle bend outward.

2. Newton’s Second Law of Motion

The rate of change of linear momentum is proportional to the applied force and change in momentum takes place in the direction of applied force.

Mathematically F & infi; dp / dt

F = k (d / dt) (mv)

where, k is a constant of proportionality and its value is one in SI and CGS system.

F= mdv / dt = ma

Examples

1. It is easier for a strong adult to push a full shopping cart than it is for a baby to push the same cart. (This is depending on the net force acting on the object).
2. It is easier for a person to push an empty shopping cart than a full one (This is depending on the mass of the object).

3. Newton’s Third Law of Motion

For every action there is an equal and opposite reaction and both acts on two different bodies

                             F₁₂         F₂₁

1                                           2

Mathematically F12 = – F21

Examples

1. Swimming becomes possible because of third law of motion.
2. Jumping of a man from a boat onto the bank of a river.
3. Jerk is produced in a gun when bullet is fired from it.
4. Pulling of cart by a horse.

Note Newton’s second law of motion is called real law of motion because first and third laws of motion can be obtained by it.

1. The modern version of these laws is

1. A body continues in its initial state of rest or motion with uniform velocity unless acted on by an unbalanced external force.
2. Forces always occur in pairs. If body A exerts a force on body B, an equal but opposite force is exerted by body B on body A.