### Laws Of Motion

Laws of Motion discovered by Newton , They are as follows ;

Law 1  :-     Every body  perseveres in its state of rest or of uniform motion in a straight line unless it will compelled to change that state by impressed force .

Law 2  :-     The rate of change of momentum is proportional to the impressed force and take place in the direction of the straight line in which the force acts .

Law 3  :-     To every section there is always an equal and opposite reaction or the mutual action of any two bodies are always equal and oppositely directed .

The first law implies :

1)-----  That the internal force in a body do not play a part in the state of rest or of uniform motion .

2)-----  The definition of an external force as that which tends to change the inertia of a body on which it acts .

The second law enables us to measure force . If a mass    m     moves with a velocity    v     then its momentum is   mv     .

According to second law ;

F  (an external force)   varies as     (d/dt) (mv)

therefore   F=K.(d/dt)(mv)  where   K   is a suitable constant

=K.m.dv/dt  ,  if    m   is a constant .

=K.m.f  ,  where    f    is the acceleration .

We now define a unite of force as that force which acting on unit mass produces unit acceleration .

therefore    1=k.1.1  so that      K=1.

therefore     F=mf

= mass .  acceleration    .