Imagine two objects. We connect one light object and one heavier object to each other by a string. Climb to the top of a tower with these two objects. It is a calm, sunny day with little wind. Once you reach the top, drop both objects from the top of a tower at the same time.
Which lands first? If you ask the famous philosopher, Aristotle, you will learn Aristotle’s laws of motion. In his work Physics, Aristotle states objects fall at a speed proportional to their weight and inversely proportional to the density of the fluid the objects are immersed in. At first pass, you might think this is a correct approximation to explain falling objects on Earth. Things fall faster in the air than water, so it seems to make sense.
Looking back at our experiment of the two objects tied together, we can test if this answer works. If the heavier object falls faster than lighter ones, the string will become tight. The lighter object would slow the fall of the heavier object. Aristotle’s theories stood for over 1000 years before someone else came along. Another famous person reportedly tested Aristotle’s principles and provided them wrong.
Leaning Tower of Pisa and Galileo Galilei
What better place to test the theory than the Leaning Tower of Pisa. Surely if two objects were dropped from the top of the tower, the heavier object would fall faster and hit the ground first. Galileo showed all bodies, regardless of their weights, fall with equal speeds. Galileo repeated the experiments he did from the height of the Leaning Tower of Pisa in the presence of other professors and all the students. Galileo was right.
All falling objects fall the same when under the same conditions… that is so long as no outside force is exerted on it. So two objects dropped from the same altitude, one a feather and hammer will fall equally. Don’t believe me? NASA tested it on the Moon. During Apollo 15 moon walk, Commander David Scott performed a live demonstration for the television cameras. Commander Scott held out a geologic hammer and a Falcon feather and dropped them at the same time. Because there is not an atmosphere on the Moon, they were essentially in a vacuum. With no air resistance force, the feather fell at the same rate as the hammer.
On Earth, and any other planet with an atmosphere, air acts as a resistance force for an object moving through it. We can get more air resistance force by increasing the surface area.
From the Apollo 15 Report:
During the final minutes of the third extravehicular activity, a short demonstration experiment was conducted. A heavy object (a 1.32-kg aluminum geological hammer) and a light object (a 0.03-kg* falcon feather) were released simultaneously from approximately the same height (approximately 1.6 m) and were allowed to fall to the surface. Within the accuracy of the simultaneous release, the objects were observed to undergo the same acceleration and strike the lunar surface simultaneously, which was a result predicted by well-established theory, but a result nonetheless reassuring considering both the number of viewers that witnessed the experiment and the fact that the homeward journey was based critically on the validity of the particular theory being tested.
Joe Allen, NASA SP-289, Apollo 15 Preliminary Science Report, Summary of Scientific Results, p. 2-11(* the 0.03-kg value is too high, typical feathers have masses between 0.0003 and 0.003 kg (0.3 – 3 grams), this may be due to a typo in the report.)
Apollo 15 Hammer and Feather experiment : Credit NASA
For the people thinking the moon landings were a myth…
The Mythbusters TV show decided to put this same concept to the test. Here a video to help you see that they repeated the same experiments. They did the experiments without a vacuum and then again with a airless chamber.
