I am trying to build a mechanical clock, but my pendulum doesn't swing for very long when stopping. Increasing mass only takes me so far. In this video, he uses a much longer pendulum than 25 cm, but somehow still yield a 1 second tick rate. How is this possible? https://www.youtube.com/watch?v=kn1OaGAae5w Also, a large part of why mine doesn't swing so long I think is that the angle I am releasing it at can only be so high due to the escape wheel it has to hit.

  • $\begingroup$ friction forces cause this but somehow i dont think a 25 cm pendulum has a perod of 1s $\endgroup$
    – joojaa
    Commented Jan 2, 2023 at 17:56
  • $\begingroup$ it does have a period of 1 second according to the equation. so what length pendulum could the guy in the video be using? $\endgroup$ Commented Jan 2, 2023 at 18:10
  • $\begingroup$ your pendulum can also be working with any fraction or product of a second too. Anyway what equation are you using? $\endgroup$
    – joojaa
    Commented Jan 2, 2023 at 21:04
  • $\begingroup$ Are you saying that your pendulum stops swinging after just a few swings? i.e. you start it and then 10 seconds later it has stopped. Or are you saying that the period of the swing is too fast? Or too slow? $\endgroup$
    – Daniel K
    Commented Jan 2, 2023 at 21:25
  • $\begingroup$ @DanielK stopping after just a few swings $\endgroup$ Commented Jan 2, 2023 at 21:29

2 Answers 2


Counting from the video, the clock does about $10$ ticks in $8$ seconds. So $10/8 = 1.25$ ticks in $1$ second, or one tick $t = 1/1.25 = 0.8$ seconds. Now importantly: the time $T$ you are getting from

$ T = 2*pi*\sqrt{\frac{L}{g}}$ is NOT the time it takes to do one tick. It is the time to do one cycle or period (as per the wikipedia article). That means "from left to right", "back to left": two ticks

That means the clock in the video has a period of $2*0.8 = 1.6 = T$. Working back to what the length of the pendulum must be to get this $T$, we get $L \approx 0.64$ meters.

  • $\begingroup$ then how does it count time properly? $\endgroup$ Commented Jan 3, 2023 at 1:08
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    $\begingroup$ @SaveerJain gears. $\endgroup$
    – joojaa
    Commented Jan 3, 2023 at 8:43

If the pendulum is stopping after just a few swings, then changing the length, mass, and initial starting angle of the pendulum probably won't help much. The most likely issue is that there is too much friction in your system. Reducing the friction (i.e. adding lubrication, upgrading to better bearings, etc) will help.

Alternatively, most mechanical clocks don't just use the kinetic energy of the pendulum to drive them. The pendulum is just an oscillator. The energy that drives the clock comes from a very large spring. You'll likely need to add such a spring.

  • $\begingroup$ or a weight on a string. $\endgroup$
    – joojaa
    Commented Jan 2, 2023 at 21:50
  • $\begingroup$ i have a weight on a string to drive it, but that just drives the gear. That part doesn't matter if the oscillator doesnt last long. $\endgroup$ Commented Jan 2, 2023 at 22:05
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    $\begingroup$ The pendulum/oscillator will never run long enough to have a usable clock on its own. It is supposed to get a little push from the escapement (which is driven by the 'weight on a string') every cycle/period to keep it going. $\endgroup$
    – Chris_abc
    Commented Jan 2, 2023 at 22:29
  • $\begingroup$ How do I maximize this push, which I think is called impulse. $\endgroup$ Commented Jan 5, 2023 at 23:00

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