Read about Big Ben this morning - the landmark clock in London, England - originally
completed in 1859. It is up for renovation for four years and the characteristic bells will be
silent. (They normally chime on the hour, and lesser bells on the quarter hour.) I started to
wonder about how such a beast (with four faces) could be kept on time.
The answer is absolutely charming (from Wikipedia):
On top of the pendulum is a small stack of old penny coins; these are to adjust the time of the clock. Adding a coin has the effect of minutely lifting the position of the pendulum's center of mass, reducing the effective length of the pendulum rod and hence increasing the rate at which the pendulum swings. Adding or removing a penny will change the clock's speed by 0.4 seconds per day.
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In physics, the center of mass of a distribution of mass in space is the unique point where the weighted relative position of the distributed mass sums to zero, or the point where if a force is applied it moves in the direction of the force without rotating. The distribution of mass is balanced around the center of mass and the average of the weighted position coordinates of the distributed mass defines its coordinates. Calculations in mechanics are often simplified when formulated with respect to the center of mass. It is a hypothetical point where entire mass of an object may be assumed to be concentrated to visualize its motion. In other words, the center of mass is the particle equivalent of a given object for application of Newton's laws of motion.
* * *
Hoora for physics. Just completed the tutorial from Khan Academy on simple pendulums
yesterday. The formula for the period T of the pendulum is given by:
arm increases T, the length of time for a cyclic restore.
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