Gravity

According to Aristotle the velocity of a falling body was proportional to its weight and this was assumed true until 1590 when Galileo asserted that all bodies fall at the same rate unless they are so light as to be hindered in their fall by the air resistance. He proved this by dropping bodies of different weight from the top of the leaning tower of Pisa. Subsequently this was proved more elegantly by allowing a feather and a weight to fall in a vacuum and it was shown both bodies fell at the same rate. The reason that the acceleration of a falling body is constant is that the weight of a body (the force on it due to gravity) is proportional to its mass. A two-pound mass is twice the weight of a one pound mass, thus, the force causing the two pound mass to fall is twice that causing the one pound mass to fall, however, as the mass is also twice as great, its acceleration will be the same.