If the net sum of forces is zero , the object moves with constant velocity.(inertial frame) But , when this centripetal thing comes in Suppose we have only a force acting perpendicular to the motion of the body. then how does this centripetal force comes in , there are 4 fundamental forces and all other forces can be taken from these forces , but centripetal force ? which fundamental force makes centripetal force ? and why is that when a satellite revolving around a planet , acted by gravity, force is equated to mv^2/r , but that is analogous to F=ma , so there is only one force acting that is gravity so satellite should fall but it doesnt ... what is my thinking lacking ?