Frequency, Period, and Amplitude

Frequency is the number which defines the number of vibrations performed by an object within one second. From this understanding, the unit of frequency of a vibration is "the number of vibrations per second" or hertz (Hz).

Period is the time needed to make one vibration. For example, if the frequency of a vibration of a pendulum is 1 Hz, then it means every vibration needs one second. This one second time is called the period of the vibration.

Amplitude is the farthest distance of displacement of a vibration. If we look at the figure on the bottom side, the amplitude is the distance between the movements.

Formulas:

The formula for frequency is the numbers of vibrations divided by time. F = n (vibrations) = ... Hertz

                                                                                                                         t (seconds)

The formula for period is one divided by frequency. T (symbol for period) =  1 = ... seconds

                                                                                  f

Questions and Answers:

1. A ruler on a table moved, performs 14 swings within 7 seconds. What is the frequency of that ruler?

F = n  = 14 vibrations = 2 vibrations/second = 2 Hz

       t       7 seconds  

2. If the frequency of a vibration is 20 Hz, what is its period?

T = 1  =  1  = 0.05 seconds

       f      20

Sources: 

- 2B Science 2nd Semester Grade VIII textbook

- http://www.calacademy.org/products/pendulum/page1.htm

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Vibration Motion

Examples of vibration motion:

A pendulum is an object hung by a string from a fixed support. When we displace the object from equilibrium, it moves back and forth around it's equilibrium position. This is called vibration.

There is a spring on a stand and load on the bottom. If we pull the load, there will be motion on the load hanging on the spring. This is called spring motion.






Vibration is something moving rapidly and continuously back and forth passing through the balance position.

Examples of vibration motion in real life:

- A bobblehead doll is an example. Once we push the head with our finger, it will continuously move around through the balance position until it stops.

- A spring horse is another example. When a child sits on it and either pulls or push the handle, it will move rapidly and continuously until it stops.

Sources:
http://www.physicsclassroom.com/class/waves/u10l0a.cfm
http://www.physicsclassroom.com/class/waves/u10l0c.cfm