  Third, Leibniz is further able to argue that the quantity of vis  viva rather than the quantity of motion is conserved. To see  this, suppose that a one pound brick, having been raised to a height  of four meters, falls on the end of a teeter-totter imparting a  motion to a four pound brick on the other end. Now if the amount of  active force is conserved – if there is as much force in the  effect as in the cause – then (by the first premise) the brick  should be raised to a height of one meter. That being the case,  however, it is clear from the preceding demonstrations that the  quantity of vis viva but not the quantity of motion will be  conserved (since the quantity of motion has decreased from 4 units to 2 units).[17] 