There is a lot of very good information on the web about pendulum theory.
This page tries to answer some of the questions specific to clock pendulums.
Some simple experiments are also outlined to help prove some of the concepts.
Typical info you are apt to find on the web about clocks
T= 2 pi*sqrt(l/g) where
T= period in seconds for one complete cycle (a Tick and a Tock)
g= acceleration due to gravity 32.2 ft/sec/sec
l= length of pendulum in feet
Forever is a very long time
We all know from experience that pendulums do not oscilate back and forth forever.
The pendulums on our clocks would quickly come to rest if the weights were removed from our gear trains.
The Escapement gives the pendulum a little push every Tick and tock.
Without this impulse the pendulum and clock would stop.
So here are some Clock pendulum questions for you
Remember our goal is to find a pendulum that will oscilate back and forth with the least amount of help from the escapement wheel. Forever would be nice but we'd accept something like 50 oscilations before it stopped. Even 10 would do it.
Compare a heavy(10 pound) pendulum bob to a light one (1 pound)
Two identical pendulums except for bob weight are released at once.
The heavy one keeps going while the light one stops.
The short one requires a little push every once in a while to keep it going but the long one just keeps on going.
Start a pendulum from a high angle.
See that most of the energy is lost in the early stages of the cycle.
This is similar once again to what happens on a playground swingset.
It's real hard to keep the kid flying high but takes no effort to gently sway back and forth near the bottom of the arc.
Makes sense that the pendulum arc be small too in our clocks.
Compare Same pendulum with the force applied at the top and bottom
If you were trying to keep the pendulum moving where would you push?
Where do most of the clocks push on the pendulum to keep them in motion? (guess near the top)
upside down escapement
Take advantage of pushing near the bottom of the pendulum