In the next few hours one will be arriving into Firenze, Italy, to attend a conference in Arcetri taking place at the last home of Galileo. Galileo famously conducted experiments from the top of the leaning tower of Pisa and discovered that all objects fall at the same rate.
Somewhere deep down we think we know this, and yet whenever I ask this question of my university students, there is a just a little bit of doubt. Wait, if a feather and a quarter are dropped from a height do they both really hit the ground at the same time? How about a blacksmith’s anvil and a feather? Is our intuition really only skewed as a result of air friction?
I demonstrate this effect by taking a 1 1/4 yard long plastic air tube into which a feather and a quarter are inserted. The tube is closed on both ends, and the ‘fall’ of these two objects is simulated within the confines of the tube by rotating the tube. As expected, the quarter hits the other end of the tube far ahead of the feather.
The air is then pumped out of the tube and the experiment retried. Now, seemingly amazingly, when the quarter and feather are dropped from one end of the tube to the other, they hit the other end of the tube at the same time.
Galileo tells us that it is the pull of gravity that determines the speed at which objects fall, and not at all how much the objects weigh.
This experiment was taken to the Moon by Apollo astronauts in the early 1970s. An astronaut stood on the Moon’s surface, held up a falcon feather and an ordinary hammer, and then dropped the two from a height of about 4 ft. Guess what – they hit the ground at the same time.
The same pull of gravity which governs the rate of fall on Earth also governs the rate of all on the Moon, and as far as we can test it, also governs the weight of fall towards every other reasonable surface in the universe that we can look (excluding black holes).