Re:Glashütte Trash Clock – A 30-minute pendulum clock made f...
by angus-g on Monday October 05, 2026 @07:32AM
(#49963501)
My interpretation was that the actual mass of the bob doesn’t contribute to the period of the pendulum. I suppose it could shift the centre of mass somewhat relative to the mass of the rod?
Re:Glashütte Trash Clock – A 30-minute pendulum clock made f...
by ninalanyon on Wednesday October 07, 2026 @05:14PM
(#49998876)
If the pendulum bar has non-zero mass increasing the mass of the bob while keeping its centre of mass at the same location on the pendulum will move the centre of mass of the combination of the two parts down and increase the period. This is a small effect because the pendulum rod is very much lighter than the bob.
The pendulum in the clock colloquially called Big Ben is regulated by adding or subtracting from a stack British pre-decimalisation one penny coins. However in this case they are placed at the top of the bob not at its centre of mass so adding a penny shortens the pendulum by moving the centre of mass of the bob up
> a pendulum oscillates is only determined by its length (and the strength of gravity), while the weight at the end of the pendulum’s rod (which clockmakers call a bob) doesn’t really matter.
This not correct. The period is determined by the distance from the fulcrum to the centre of mass. The position of the bob does matter. On my grandfather clock there is a small screw that adjusts the position of the bob and hence the length of the pendulum so that you can regulate the clock.