I was wondering how did Sir Newton measured motion of objects (non celestial ones). What was his toolskit at the time?

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    $\begingroup$ 1. I'm not sure Newton ever "measured motion". 2. This question would probably be better at History of Science and Mathematics. $\endgroup$ – ACuriousMind Jul 17 '16 at 20:24
  • $\begingroup$ physics.stackexchange.com/q/2644. In general it's not a good idea to assume that the demonstration experiments we are doing today for students have much in common with the discovery or deduction of laws of nature in the past. Science and history are much more complex than that. This is especially true in mechanics where testing Newton's laws directly would actually require orbital spaceflight. $\endgroup$ – CuriousOne Jul 17 '16 at 21:00
  • $\begingroup$ @sammygerbil: The crucial experiments in this case are all space based. Celestial mechanics was the target, not motion on Earth. The required observations were all made by Galileo, Copernicus, Kepler and others. Newton just had to put it together. That's no different from what Einstein did, who also never touched an actual ruler... but he knew what it had to do to make sense of Mercury's perihelion drift! $\endgroup$ – CuriousOne Jul 17 '16 at 21:05
  • $\begingroup$ While it doesn't directly answer your question, I suspect you would be interested in this video demonstrating how Newton determine the speed of sound. Lots of things wrong with that movie, but it's a start. $\endgroup$ – Floris Jul 17 '16 at 21:26
  • $\begingroup$ Might this question be better on "history of science and mathematics"? $\endgroup$ – Floris Jul 17 '16 at 21:53

The most famous "terrestrial" experiment that I know of was the measurement of the speed of sound in Nevile's Court in Trinity College, Cambridge. As the tour guides will tell you, Newton stomped his foot and listened for the echo from the wall on the opposite end of the North Cloister. He timed the echo by making a (short) pendulum, and adjusting the length until the round trip time of the sound equalled the period (half period?) of the pendulum.

I have not been able to find an authoritative description - but anecdotally I have heard that he actually clapped (or stamped his foot) repeatedly, and either tried to drown the echo with the next clap, or clap rhythmically (so that there is equal time clap-echo-clap-echo). If you were to employ a person with some musical talent (for example, a drummer) to do this, you would then be able to count the number of round trips of sound over a much larger (and more accurately measured) time interval.

The problem with the "really short pendulum" is that inertia of the bob becomes a significant factor - and this will mess up your calculation of the period. Also, a short pendulum is likely to have an angle that not "small" - and when the small angle approximation breaks down, the period of the pendulum no longer follows the simple equation. I suspect that Newton knew that...


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