1. Waves Basics

2. What is a mechanical wave?
A mechanical wave is a disturbance in matter that carries energy from one place to another.
The matter which the wave travels through is the medium.

3. What causes a mechanical wave?
A mechanical wave is caused by a source of energy producing a vibration that travels through the medium.

4. Two types of Mechanical Waves
There are two types of waves:
Transverse
Longitudinal

5. Transverse Waves
The movement of the wave is at a right angle to the medium
Examples:
Light
Water waves
Electromagnetic waves 5

6. Parts of a Transverse Wave

7. Parts of a Transverse Wave
Midpoint: The point at which the medium was at rest before the wave.
Crest: The highest point of the wave above the midpoint.
Trough: The lowest point of the wave below the midpoint.

8. Longitudinal Waves
The direction of wave travel occurs along the direction in which the source vibrates.
This causes the medium to be temporarily compressed and stretched. 8

9. Parts of a Longitudinal Wave

10. Parts of Longitudinal Waves
Compression – areas where the medium is closer together.
Rarefaction – areas where the medium is stretched apart. 10

11. Frequency The number of vibrations in a given time (1 second)
Frequency = # of waves ÷ # of seconds
Unit of frequency is the Hertz
I cycle per second
1 wave per second

12. Example Problem:
A pendulum completes one cycle every two seconds. What is the frequency of the pendulum?

13. Answer Frequency = # of cycles ÷ # of seconds.
Frequency = 1 cycle ÷ 2 seconds
Frequency = 0.5 Hertz

14. Wavelength
Wavelength is the distance between a point on one wave and the same point on the next cycle of the wave.
Frequency and wavelength are related.
As the frequency increases, the wavelength decreases.
As the frequency decreases, the wavelength increases.

15. Period The amount of time it takes a wave to complete one cycle.
Period = 1/Frequency
Unit is seconds

16. Example Problem: A pendulum completes 4 cycles in 3 seconds.
What is the frequency of the pendulum?
What is the period of the pendulum?

17. Answer: Frequency = # cycles ÷ # of seconds Period = 1/ Frequency
Frequency = 4 cycles ÷ 3 seconds
Frequency = hertz
Period = 1/ Frequency
Period = 1/1.3333
Period = 0.75

18. Wave Speed Two possible formulas: Wave speed = wavelength x frequency
Wave speed = wavelength /period 18

19. Example Problem:
In 30 seconds, 2 waves hit a dock. The wavelength is 5m.
What is the frequency of the wave?
What is the wave-speed?

20. Answer: Frequency = cycles ÷ time Wave speed = Wavelength x frequency
Frequency = 2 waves ÷ 30 seconds
Frequency =1/15 hertz
Wave speed = Wavelength x frequency
Wave speed = 5m x 1/15 hertz
Wave speed = 0.33 m/s

21. Amplitude
Amplitude is the maximum displacement of the medium from its rest position.