1. Period & Frequency
Ch – 25.2

2. Wave
Repeating disturbance or movement that transfers energy through matter or space
Periodic motion
What types of objects/source cause transfer of energy through waves?

3. Waves and Energy Waves carry energy not matter!
Waves travel only as long as they have energy to carry
Wave intensity decreases with distance from the original source of energy

4. Period Time for a back and forth swing Example: pendulum
Directly proportional to the square root of the length and inversely proportional to the acceleration due to gravity T= 2π√(L/g)
Does not depend on mass

5. Practice Question:
Which has a longer period: a long pendulum or a short pendulum?
Long pendulum

6. Frequency: how often a vibration occurs
Measured in hertz (Hz)
Frequency and period are inversely proportional to each other
Frequency = 1 / period
Period = 1 / frequency

7. Practice Question:
If the period of the vibration is 2 seconds, what is the frequency?
Frequency = 1 / period
Frequency = 1 / 2 = ½ Hz

8. Practice Problem 2
100 waves pass a dock in 10 seconds. What is the frequency of the wave? f = number of waves/second = 100/10= 10 Hz What is the period of the wave? period= time for one wave = 10/100= 0.1 seconds