A gravity pendulum is a weight on the end of a rigid rod, which, when given some initial lift from the vertical position, will swing back and forth under the influence of gravity over its central (lowest) point. A torsion pendulum consists of a body suspended by a fine wire or elastic fiber in such a way that it executes rotational oscillations as the suspending wire or fiber twists and untwists.
This simple pendulum is an ideal tool for teaching and
learning the basic concepts of harmonic motion. The
concepts of cycle, period, frequency, and amplitude are
intuitively illustrated. Students can change three variables: the
length of the string, the weight of the swinging bob, and the
amplitude
As you watch moving things, you see two different kinds of motion. One kind of motion goes from
place to place without repeating. This is called linear motion. The concepts of distance, time, speed,
and acceleration come from thinking about linear motion.
The second kind of motion repeats itself over and over. This is called harmonic motion and is the
subject of this section. The word "harmonic" comes from harmony which means "multiples of."
Harmonic motion has multiple cycles, repeated over and over. A pendulum swinging back and forth is a
good example of harmonic motion .
Galileo Galilei discovered that pendula exhibit regular periodic motion, a feature which he correctly speculated would make them useful for timekeeping devices such as clocks. This has led to their frequent metaphorical use as a way of describing the passage of time, or the experience of it. The mass of the weight on the pendulum does not affect the outcome, just as it does not affect the outcome of dropped objects.
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