  Using these four premises, Leibniz attempts to establish three  principal conclusions. First, he argues that Descartes’s quantity of  motion is not an adequate measure of force. To see this, suppose that a four pound brick falls from a height of one meter in one second.  Its quantity of motion = 1 m/s × 4lbs = 4 units. By Galileo’s  Law it follows that a one pound brick dropped under similar  circumstances will travel four meters in two seconds (since the  distance traversed is proportional to the square of time).  The quantity of motion of a one pound brick falling through a  distance of four meters therefore = 2 m/s × 1lbs = 2 units.  Since by the second premise the force of the two bodies is equal, but their quantities of motion are unequal, Leibniz concludes that  quantity of motion is an inadequate measure of force. 