Centripetal Force:

Any kind of motion in curved path represents accelerated motion, and needs a force directed toward the center of curvature of path. This force is called as centripetal force which means "center seeking" force. The force has the magnitude which is given by

F_c = mV² / r

Component of the force acting on a body in curvilinear motion which is directed toward the center of curvature or axis of rotation. The centripetal force is essential for an object to move with circular motion. Swinging a mass on a string requires string tension, and the mass will travel off in a tangential straight line if the string breaks. The centripetal acceleration can be derived for the case of circular motion since the curved path at any point can be extended to a circle the centripetal force is proportional to the square of the velocity, implying that a doubling of speed will require four times the centripetal force to keep the motion in a circle. If the centripetal force should be provided by friction alone on a curve, an increase in speed could lead to an unexpected skid if friction is insufficient. Whenever an object moves in a circular path we know that the object is accelerating as the velocity is constantly changing direction.  All the accelerations are caused by net force acting on the object.  In the case of an object moving in the circular path, the net force is a special force called as centripetal force .Centripetal is the Latin meaning of "center seeking".  So a centripetal force is the center seeking force which means that the force is directed toward the center of the circle always.  In absence of this force, an object will simply continue moving in the straight line motion.

The Centripetal force keeps the planets in orbit. According to Newton's first law, all the masses have inertia and like to move at the constant speed in a straight line. The earth wants to move straight but it is prevented from doing so because of the sun's gravity.