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### Pseudo or Fictitious forces

Consider a particle P in stationary frame of refrance S in which no force is acting i.e., a=0. If any other frame of refrance S' is moving with acceleration a w.r.t. frame S, then an acceleration -a0 appears to be acting on the particle P w.r.t. S'. Therefore a force -ma0 seems to be acting on the particle P due to the accelerated motion of the frame S'. This force is known as Pseudo force or fictitious force. Therefore pseudo forces are the force which does not actually acts on the particle but seems so because of the accelerated motion of the refrance frames are. This accelerated frame of refrance S' is a non inertial frame of refrance . If due to force FR on the inertial frame of refrance , the particle seems to suffer an acceleration aR then by Newtonian mechanics FR=maR Therefore resultant force on particle in accelerated frame is
F=FR+Fa
ma=maR+(-mF0)
or,
a=aR-a0
where Fa is fictitious force. Direction of fictitious force is opposite to the accelerated motion of S' frame of refrance.

### Law of conservation of linear Momentum

Law of conservation of momentum is one of the basic laws and is derived from Newton’s Laws of motion. This law always holds true even in the situations where Newton’s laws of motion fails to hold. This law states that in the absence of resultant external force acting on the system , the total linear momentum of the system always remains constant i.e.,

p=p1+p2+p3+……+pn

This is law of conservation of linear momentum for system of particles. For individual particles momentum may change but their total momentum remain unaltered in absence of external forces.

Now the law of momentum is fundamental and exact law of nature. No violation to it has ever been encountered.