We decided to replicate Galileo's inclined plane experiment because it was so fundamental to new concepts of motion in Galileo's time. We based our experiment on Galileo's own description of the inclined plane in his book Discourses on Two New Sciences (1638):
Our own construction entailed planing at a 45 degree angle one edge each on two 16-foot two by fours, which when nailed together formed a groove. We sanded and oiled the groove to create a low-friction effect like Galileo's parchment. Instead of a small bronze ball, we used a three-quarter inch steel ball bearing. We added a metal piece to the end of the inclined plane, against which the ball struck at the end of each run, to make our timing precise. Click here for a more detailed description of our inclined plane.
We also replicated Galileo's apparatus for timing the inclined plane experiment. Galileo describes his water clock in Discourses on Two New Sciences (1638):
Our water clock consisted of a plastic bucket with a small hole drilled in the bottom, into which we placed a length of plastic tubing. When filled with water the bucket emitted a thin stream of water through the plastic tubing. We controlled the flow of water by clamping the tubing with a small metal clamp.
We marked our inclined plane at one quarter, one half, and three quarters its length. Starting with the full length of the plane, we rolled the ball twenty times down each length, timing each trial with our water clock. Like Galileo, we weighed the water from each trial so as to determine the ratio of times for each length.
Our experiment proved that Galileo could have attained the accuracy which he claimed for this experiment. Our findings also point clearly to the concept of acceleration: the ball travels down one quarter of the plane in half the time it takes to traverse the entire plane. Aristotle would have posited, of course, that the ball's time would be directly proportional to the distance it traveled. Andrew Irving has created graphs which clarify Galileo's discovery that the ratio of the distances traversed by the ball is proportional to the ratio of the squares of the time.
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