Force is a push or pull, which changes or tends to change the state of rest or uniform motion, speed, shape and direction of motion of a body.
The SI unit of force is Newton and CGS unit is Dyne .
Force of gravitation exist between any two bodies in the space. The forces that attract two bodies is described by gravitation. Gravitation has various theories surrounding it which are :
Geocentric theory: Defined in 16th century. Geocentric theory is outdated as a result not in use in present day.
Heliocentric theory: Defined in 16th century. Heliocentric theory is the governing theory of gravitation in the present.