Science Puzzle
Which Hits the Ground First?
An astronaut standing on the Moon holds a hammer in one hand and a feather in the other, both at exactly the same height. The Moon has no atmosphere, so there is no air at all.
The astronaut opens both hands at exactly the same moment. Which one hits the ground first?
The Answer
They land at exactly the same time.
Gravity accelerates every falling object at the same rate, no matter how much mass it has. A heavier object is pulled with more force, but it also needs more force to get moving, and the two effects cancel out exactly. On the Moon everything falls at about 1.6 metres per second squared, hammer and feather alike.
On Earth the feather loses the race, but not because it is lighter. Air resistance pushes back against the feather far more effectively than against the compact hammer. Remove the air and the race is always a dead heat.
This is not just a thought experiment. In 1971, Apollo 15 astronaut David Scott stood on the Moon, dropped a hammer and a falcon feather together on live television, and watched them strike the lunar dust at the same instant. As he put it, Galileo was right.
The principle: Free fall. In the absence of air resistance, all objects fall with the same acceleration regardless of their mass.