So, how do we stop the weight, string and axle from accelerating?
We attach a gear to the axle which has the string and weight attached to it. The gear has teeth, but the teeth are not symmetrical. One side of each gear tooth is tapered, looking like a “ramp”; the other side is cut somewhat straight and mostly aligned with the center of the gear. This is the “escapement gear” (you’ll see why it’s called that later). The escapement gear is attached to the rod, and it still wants to pick up speed as the earth’s gravity pulls down on the weight and string. We still need a method to slow the gear down, so that it turns at a measured rate. Or, we need something to consistently stop the escapement gear for a small amounts of time, then release it for small amounts of time. That cycle has to keep going. This is where the oscillations of the pendulum come into play.
We now take a rigid stick and attach a weight to one end (this weight is called a “bob”), and we”ll add a crossbar with two teeth to the other end (the crossbar is called a “pallet”). Imagine an elongated “T”, with the bob on the bottom and the pallet on the top. It’s like using a serif font: the two serifs on the cross of the “T” point downward, so do the teeth on the pallet. This “T” is our pendulum. As the bottom of the pendulum swings “right”, the left tooth of the pallet moves downward and meshes with the gears on the escapement, causing it and the weighted string to stop moving. Because of its oscillating characteristics, the pendulum will reach its full travel toward the right and will then begin moving back the other way. As it passes the bottom of its travel, the left pallet tooth now moves upward and releases the gear, allowing the escapement gear to “escape” (thus, the name “escapement gear”) and the weighted axle begins moving again. This time, as the pendulum passes center and continues its travel to the left, the right-side pallet tooth moves downward and it will now mesh with the escapement gear, causing the axle to stop movement, once again. The pendulum reaches its full travel to the left and once again begins moving toward the right. Thus, the axle with the weighted string is allowed to move, then stop, every time the pendulum makes full travel in each direction. They’ve done it! The weighted axle will not accelerate and use up all of its potential energy in a very short time, because it repeatedly stops moving. We have regulated the movement with the pendulum, and its movement is now predictable and can be transferred in a practical way.
The next post will explain what keeps the pendulum swinging, and not slowing to a stop.
