Newton's Laws Of Motion
NEWTONS FIRST LAW:If no external force acts, a body continues to be in its state of rest or of uniform motion along a straight line. (OR)
If no external force acts, we can also say that “bodies” go on doing what they are doing.
INERTIA:
Inertia is the property of a body by which unable to change it’s state by it’s own mass is measure of inertia
Force is that which changes or tends to change the state of a body Inertia means resistance to change state.
The inability to change the state of rest of a body by itself is known as inertia of rest.
The inability to change the state of motion of a body by itself is known as inertia of motion.
The inability to change the state of direction of a body by itself is known as inertia of direction.
FORCE
Force is that which changes or tends to change the state of a body Force is a vector. It is always in the direction of change in momentum. Force is also
always in the direction of acceleration.
SI unit of force is newton (N). If a force acting on a mass of 1 kg produces in it an acceleration of 1 m s-2 in its direction, it is called a newton.
CGS unit of force is dyne. If a force acting on a mass of 1 gm produces in it an acceleration of 1 cm s-2 in its direction, it is called a dyne.
f=ma
LINEAR MOMENTUM
Consider two balls A and B. Let ball A be heavier than the ball B. i.e. mass (m1) of ball A isgreater than the mass (m2) of the ball B. Suppose both balls are moving with same velocity \( \vec v\).
Theforce require to stop ball A more than the force required to stop ball B. This shows that the heavierball has more quantity of motion than the lighter ball. Thus, quantity of motion of a
body is directlyproportional to the mass of the body.
Now consider two balls of same mass moving with different velocities. The force required to stop the fast moving ball is more than the force required to stop the slow moving ball. Sothe quantity of motion of the body is directly proportional to the velocity of the ball.
Conclusion :The quantity of motion of the moving body is proportional to
(i) mass of the body
(ii) velocity of the body.
This quantity of motion possessed by a moving body is known as momentum of the body. ( or ) The total quantity of motion contained in a body is called momentum.
MATHEMATICAL EXPRESSION : Momentum of a body is equal to the product of the mass (m) of the body and the velocity (\( \vec v\)) of the body. It is denoted by \( \overrightarrow P\).
Thus, momentum = mass × velocity
\( \overrightarrow p = m\overrightarrow v\) * momentum is a vector quantity
Note :- The direction of momentum of a body is same as that of the direction of the velocity of the body.
UNITS OF MOMENTUM: S.I. unit of momentum = S.I unit of mass × S.I unit of velocity = kg × m/s = kg m/s. Similarly C. G. S. unit of momentum is g cms–1.