Originally Posted by
supramax
Andy_ K,
It's NOT a vacuum example. It's proven in a vacuum (with the feather/hammer or whatever). The air resistance is negligable with a penny and a 5 lb barbell plate. Drop them (same time and height) and they'll reach the ground at the same time.
If the penny is wearing a skinsuit and an aero helmet it will reach the ground faster unless the hammer is using a disc wheel, shaved its legs, and put tape over its shoe laces. In that case it's too close to call.