Examination of the Question 19 in the Mechanics of Aristotle

Abstract

Here by the way the opinion of Aristotle on the cause of the energy of percussion presented in his Mechanics can be refuted. He indeed seeks the reason why, if somebody puts a big axe on a piece of wood and adds over it a heavy wooden weight, whatever his attempts, he does not split the wood. If actually he raises the axe and strikes, he splits the wood although the weight which struck is much smaller than that which is on the wood and compresses it. He answers that everything is done with movement, and the weight itself of gravity is more in movement while it moves than when it rests incumbent. Consequently, a mobile does not move in an innate motion of gravity but actually it moves following gravity and following the action of a striking object. From this, his followers infer that a pouncing body acts not only through its innate gravity but also through the gravity which it acquires in moving, that the movement adds weight to the weight or that gravity is increased in movement. Therefore, it works more efficiently. This is certain, they say, since heavy bodies when falling also impel projectiles more in their progress, as if they were heavier.