1. The Loving Relationship Between Frequency and Period Ch 25.1

2. Objectives 1. Describe period of pendulum

3. Tappity Tap  Tap, tap, tap  Notice how frequently I’m tapping. What’s this called?  Frequency:  how often a vibration occurs  i.e. 3 taps per second or 3 hertz (Hz)  Hertz = “per second”

4. What is a period?  Period:  the time it takes to complete one cycle  i.e, if 3 taps per second, -> period = 1/3 second  All you do is divide 1 (for 1 second) by the frequency (# of taps)  Demo  Swing pendulum for 10 seconds. How do we find the period?  Divide # of swings (frequency) by time (10 seconds)  Let’s try...  In case you were wondering, Galileo was the first one to discover this.

5. What’s the relationship between T & f?  Frequency = 1/Period  Period (T) = 1/Frequency  Examples:  I can dribble a basketball 2 times in one second. What is the period?  1 divided by 2 = 1/2 of a second; period = 0.5 sec  I am a world champion speed eye-blinker. The period of one blink is 0.3 (3/10) of a second. What’s the frequency?  1 divided by 0.3 = 3.3 blinks per second or 3.3 Hz

6. Frequency in Nature Can anyone guess the frequency of a hummingbird’s wings? Can anyone guess the frequency of a hummingbird’s wings? Up to 200 Hertz! Up to 200 Hertz! What’s the period? What’s the period? 1/200sec or 0.005 seconds. 1/200sec or 0.005 seconds.

7. Practice Questions 1. What is the frequency in vibrations per second of a 100 Hz wave? 100 times per second 100 times per second 2. The Sears Building in Chicago sways back and forth at a frequency of 0.1 Hz. What is its period of vibration? 1 vib/0.1 Hz = 10 seconds 1 vib/0.1 Hz = 10 seconds