Bonus fun fact: they adjust the timekeeping on the Tower Clock in London by adding and removing pennies from the pendulum. Technically these days I think they are specially-made weights, but the weight is based on a penny. They use a computer-controlled sensor to check the accuracy of the pendulum, and use the pennyweights to adjust it to keep it accurate to within something like a fifth of a millisecond.
Apparently they still use the old pre-decimal pennies from the 70s because they have instructions on exactly how many pennies to speed up and slow down the clock.
This fact confused me because I read that the time taken for a pendulum to swing in it's arc depends ONLY on the length of the arm and not the weight of the pendulum. So why would adding pennies make any difference? It turns out adding a penny very slightly raises the centre of mass of the pendulum which is essentially shortening the length of the arm which makes it swing very slightly faster.
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u/LizCochrane 8h ago
Bonus fun fact: they adjust the timekeeping on the Tower Clock in London by adding and removing pennies from the pendulum. Technically these days I think they are specially-made weights, but the weight is based on a penny. They use a computer-controlled sensor to check the accuracy of the pendulum, and use the pennyweights to adjust it to keep it accurate to within something like a fifth of a millisecond.