Tag Archives: pendulum

A dumbbell idea

The problem with clocks in the 1700s: the ship’s rocking messed up a clock’s pendulum movement; the salty sea air corroded the metal gears; changes in temperature and humidity made metal clock parts expand & contract. All these things made a clock inaccurate—it was too slow or too fast.

Harrison came up with some innovative ideas to counter-act these problems. The first one was a dumbbell-style of pendulum. Instead of a rod with a weight at the bottom swinging from an axis, Harrison put the axis in the middle of 2 rods with weights at top and bottom—then he connected them with springs so they would keep moving back and forth no matter how the ship bounced around.

Standard-issue pendulum at the left; Harrison’s dumbbell movement at the right.

Start at 1:00—

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Like a pendulum do

One time while sitting in church, Galileo noticed a lamp suspended from the ceiling that was swinging back and forth. That motion is known as a pendulum. As it swung, he observed the lamp kept the same rate of speed. It occurred to Galileo that you could use a pendulum’s regular rate of speed to regulate a clock.

We learned that in Galileo’s time a clock was powered by a weight that slowly released its energy as it was pulled to Earth by gravity. The mechanism that slowed down—regulated—the weight’s energy is called an escapement. Galileo thought to replace the verge and foliot escapement with a pendulum escapement.

Just like the verge and foliot, as the pendulum swings back and forth it allows a gear to move forward a little bit just before a pawl stops it—until the pendulum swings to the other side. The pendulum escapement releases-stops-releases-stops the gears as they move the hands of the clock. Here is an excellent animation of Galileo’s escapement. Notice how when the gear turns it gives the pendulum a teensy little push.


Watch this guy make a wooden pendulum clock: https://www.youtube.com/watch?v=rvU37Aho4FA

Here’s some terrible music:

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