which the impetus tends to move it, this impetus is continually weakened. Therefore the movement of the stonewill become continually slower, and at length, the impetus is so diminished or destroyed that the gravity of thestone prevails over it and moves the stone down towards its natural place.
A. C. Crombie, Medieval and Early Modern Science</>This theory is sometimes called the Animistic theory of motion since it envisions a "life force" being associatedwith motion.Newton's 1st law is often very difficult to grasp because it contradicts various common-sense ideas of motion that may havebeen acquired from experience in everyday life. For example, unaccounted for forces like friction might cause a ball rolling onthe playground to eventually stop, even though no obvious forces seem to be acting.When studying Newtonian mechanics, it is best to remember this as two laws:1. If the netforce (i.e., vector sum of all forces) acting on an object is zero, the object will keep moving withconstant velocity (which may be zero).2. If an object is moving with constant velocity (not speed), that is, with zero acceleration, then the net force actingon that object must be zero.Complete the following sentences to see if you can apply these ideas.Part AIf a car is moving to the left with constant velocity, one can conclude that