Brainstorm with a classmate and find 5 more objects that display periodic motion.
We now must become familiar with some basic terminology, which is used to describe this type of motion.
Vibration (N)  One complete to and fro motion.
Period (T)  The length of time required for one vibration. It is expressed in seconds.
Frequency (f)  The numbe of vibrations per unit time. One vibration per second is one hertz (Hz).

Note:
For a recording timer a record of periodic motion occurs when the striker hits the
recording tape at regular intervals. The space between the dots on a recording tape is called one dot interval. One vibration is represented by one dot interval.
Sample Problem 1
What is the Period of a pendulum in a grandfather clock if it takes 17s to make 11 vibrations?
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Answer:
The period of the pendulum of the gradfather clock is 1.55 s.
Sample Problem 2
If it takes 13s to make 72 vibrations of the striker, what is the frequency of the timer?
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Answer:
When you look at the equations for the period and the frequency of the timer you will notice that these quantities have an inverse relationship which can be stated mathematically as:
Sample Problem 3
A recording timer was used to make a permanent record of motion on a recording tape. Christopher counted 267 dot intervals between the starting line and the finish line on the tape. It took 3.6 s for the tape to pass beneath the striker from start to finish.
Calculate the:
frequency of the timer.
period of the timer.
change in time between the third and sixth dot (see Image A).
number of dot intervals for a change in time of 1.2 s.
number of dots for a change in time of 1.2 s.

Image A:

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Answer:
e) The number of dots is equal to more than the number of dot intervals for the same time period. Therefore the number of dots for a change in time of 1.2 seconds is 90 dots.
Note: Part c) and d) can also be solved by manipulating the period equation. Your answers will vary slightly because of significant figures.
Periodic Motion  The Pendulum
