Step 3: The Pendulum
Pendulums are an interesting mechanism. They are a weight at the end of a string or pole, with a pivot at the opposite end of the weight. The period of a pendulum is the time it takes to go from one side to the other and back again. The neat thing about pendulums is that this time, or period, is not dependent on the amount of weight or length of arc, it's dependent on the length of the pendulum. So, if you had a 2 foot long pendulum with a 5 pound weight, pulled to the right at 90 degrees, it would take the same amount of time to swing across and back as a 2 foot long pendulum with 2 pounds of weight pulled to the right at 30 degrees. The weight at the end of the pendulum does affect how many times the pendulum will swing. So the pendulum with the 5 pound weight will swing for a longer amount of time, than the 2 pound weight. This is helpful because we want to keep the pendulum swinging. You can, however, have too much weight. As we will see next, the escapement helps give the pendulum a push. If you have too heavy of a weight, you will not have enough energy to keep it swinging.
For our clock, we want to have a period of 2 seconds. That way, it will take the pendulum 1 second to swing to one side. With each swing the escapement will allow the escape gear to turn one tooth at a time. If the period is 2 seconds, this will basically make the escape gear our second hand since it is rotating one tooth every second. For a period of 2 seconds we need it to have a length of 1 meter. Since our escape lever will have 2 teeth, one to stop the escape gear at each end of the pendulum swing, our pendulum will need to have 30 teeth. It will make one rotation every 60 seconds. Many pendulum clocks have the escape gear on the second hand axle. That is what we are going to do.
As the pendulum swings back and forth, it rotates the escape lever in and out of the escape gear. This causes the clock gears to stop and start rotating every second. The lever is designed so that as it is moving out of the escape gear, the gear gives it a little push. This push is enough to keep the pendulum swinging.