Vector diagram showing how an object travelling in uniform circular motion moves off at a tangent once there is no centripetal force.

Vector diagram showing how an object traveling in uniform circular motion moves off at a tangent once there is no centripetal force.

As we move from Kinematics, in which we discussed HOW objects move to Dynamics, in which we discuss WHY, let us reprise the primary conceptual movement from Kinematics to Dynamics.

Force is a concept of Dynamics. Acceleration is described in Kinematics. Under the influence of a net force an object accelerates. Its velocity changes, speeding up, slowing down, or changing direction.

Net force and acceleration always exist together. If an object is accelerating, a net force must be acting upon it. Almost every MCAT has some question that turns on your comfort with the idea that acceleration does not occur without a force. If there is no force, the object maintains constant velocity.