Force is that external cause which change present position of body(rest or motion) or changes it shape or size.
It's Si unit = Newton
CGS= Dyne
1 N=10^7 dyne
F=MA where m = mass a-acceleration
It change shape and size of body and change its present position 
what is the ans for cgs?
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Force is an external effort that causes an obj. to undergo a certain change,either movement,direction,or geometrical construction.

SI unit----> Newton
CGS unit----------->Dyne

1 newton =  10^{-5} dyne
Formula------------->F= Mass* Acceleration

when a force applied on a oj. then its position changes .it's the effect of force