Engineering Expert Witness Blog

      Picture yourself holding a feather in one hand, a hammer in the other.   Your buddy has bet you that if you simultaneously drop them, the hammer will hit the ground first, and he’s got a beer riding on it.

      This exact experiment was performed in 1971 by Apollo 15 Astronauts David Scott and Jim Irwin when they landed on the moon.    We’ll tell you how it turned out later, but first let’s review the history behind the study of falling objects.

      Aristotle, the ancient Greek philosopher, would have bet with your buddy.   Back in the 4^th Century BC he developed a theory of gravity to explain the physics behind falling objects.   He asserted that the heavier the object, the faster it will fall.   His theory seems intuitively obvious on its face, but although Aristotle was a great philosopher, he was a lousy scientist.   He never ran tests to actually prove his theory.   Nevertheless, it was accepted by academics of his time, and it remained the theory of choice until Galileo came along in the 16^th Century.

      Galileo was a scientist, and he came up with his own theory concerning falling objects.   He believed that all falling objects continue to accelerate, picking up speed as they fall, and that this rate of acceleration is the same for all objects, regardless of their weight or density.

      The story goes that in 1589, at the age of 25, young Galileo attempted to prove his theory by climbing to the top of the Leaning Tower of Pisa with two balls in hand, one large and heavy, the other small and light.   He dropped them at the same time, and guess what happened?

      Both balls hit the ground at almost the same time.   They would have hit the ground at precisely the same moment had there been no air resistance, a subject which will be discussed at length later in this blog series.

      Because Galileo’s experiment was subject to the dense atmosphere of Earth, the influence of air resistance prevented him from proving his theory correct, however he did manage to prove Aristotle’s theory wrong because the balls did not strike the ground at significantly different times.

      We’ll see how the astronauts’ experiment turned out next time.

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