If pendulum eventually stops due to air friction why pendulum of pendulum clock never stops?

  • 4
    $\begingroup$ There's a small weight attached to the pendulum that slowly lowers over time. You have to wind it up periodically. $\endgroup$
    – AGML
    Jun 19, 2017 at 4:24
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    $\begingroup$ Pendulums on pendulum clocks can stop due to air friction as well. $\endgroup$
    – Brödinger
    Jun 19, 2017 at 4:25
  • $\begingroup$ Of possible interest is this aapt.scitation.org/doi/abs/10.1119/1.4705517 $\endgroup$ Jun 19, 2017 at 4:51

1 Answer 1


It will stop in a few minutes if left on its own. But pendulum clocks have mechanisms to keep the pendulum moving that need to be manually re-energised occasionally. A common one is to have a weight on a chain. Each swing of the pendulum, the weight drops very slightly, giving just enough energy to keep the pendulum moving. And every day or so, someone has to reset the mechanism by pulling the weight back up to the top again.

And the biggest energy loss of the pendulum is not due to air friction but mechanical friction in the clock mechanism of the hands etc that the pendulum drives around.

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    $\begingroup$ Hi Phill. I've edited what I think is your phone's autocorrect being unhelpful. You might want to check that I've got this right. $\endgroup$ Jun 19, 2017 at 5:19
  • $\begingroup$ @JohnRennie I gotta agree on that one. Sometimes, I think autocorrect should be called as autowrong. $\endgroup$ Jun 19, 2017 at 8:12
  • $\begingroup$ @JohnRennie thanks. That's what I get for posting when tired :) $\endgroup$
    – PhillS
    Jun 19, 2017 at 9:34

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