Newton’s laws of motion tell us the following:

• First law – An object undergoing uniform motion, whether remaining at rest or moving in a straight line at a constant speed, will continue to do so until it is acted on by a net, external force.
• Second law – If an object is acted on by a net, external force, the magnitude of the object’s acceleration will be directly proportional to the magnitude of the net force and inversely proportional to the mass of the object.
• Third law – When one object exerts a force on a second object, the second object will also exert the same type of force on the first that is equal in magnitude and points in the opposite direction.

Together, these laws allow us to determine how the forces acting on an object cause it to accelerate.  Once we have used Newton’s laws to solve for an object’s acceleration, we can use our kinematic equations to describe the object’s motion.  Problems like these, requiring Newton’s laws and kinematics, are the heart of the vector approach to classical mechanics.