# Newton’s three law of motion definition

INTRODUCTION

First law of motion –A body continues in its state of rest or uniform motion in a straight line in the same direction unless some external force is applied to it.

The tendency of bodies or objects to remain in the original initial state of rest or uniform motion is called inertia, inertia is of two types

1-Inertia of rest and

2 -Inertia of motion

Also, the external force which is accountable to change the state of the bodies provides us the definition of force

Second law of motion –The rate of change of linear momentum is directly proportional to the force applied and displacement takes place in the direction applied force –

Linear momentum (P=MV ) mass & velocity

F directly proportional to dp/dt

F=k.dp/dt

F=k.d(mv)/dt

F=km.dv/dt        where m=mass

=km    k=proportionally constant

K=1              dv/dt=a (acceleration)

F=ma

Force = mass . acceleration

Unit of  Force –‘Newton ‘kgm/s2

If the acceleration of the body is zero( a=dv/dt=0) the body will move either constant velocity or be in a position of rest. This implies that in the absence of an external force, the body either moves with constant velocity or comes to rest. This also concludes that in the absence of an external force the inertia of a body is conserved.

Third law of motion –To every action, there is an equal and opposite reaction.

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