8-Mechanical Waves

Slideshows:Waves and Sound Notes

Textbook: Chapters 20 in Mastering Physics (get online code for registration on about page of google classroom)

Objectives:

Classifying/defining/describing waves
- Waves are traveling disturbances that transfer energy and momentum without transferring mass.
- differentiate between longitudinal and transverse waves.
- mechanical waves require a medium. electromagnetic waves do not.
- Explain waves (like sound) in terms of a transfer of energy and momentum.
- The energy of waves (like sound) depends on and increases with amplitude.
Wave properties
- Understand how to measure and explain the following:
  - amplitude
  - frequency (cycles per second)
  - period (repeat time)
  - wavelength (repeat distance or ration of v/ƒ)
  - wave speed
  - energy
- wave speed is dependent on the medium, not ƒ or λ
- observed wave frequency can be altered by relative motion between the source and the observer
Wave interactions.
- colliding waves
  - pass through each other, rather than bounce back
  - add their displacements (superposition)
  - can produce amplitude variations if not the same frequency
- standing waves
  - explain using reflection principles for confined waves
  - identify nodes and anti-nodes
  - explain examples of stringed and tubed instruments
  - possible wavelengths depend on the size of the region the waves are confined to
- Explain beats based on frequency difference

Equations:

There is only 1 primary equation:

In addition, you should know these variations/derivations:

Terms to know:

Make your own flash cards or use the electronic ones I made at quizlet.com (or in the Quizlet app on your phone) and here is the link for them: https://quizlet.com/_25opqj.

Standing Waves Help:

This animation can help you understand not only how harmonics fit on a string, but what happens when they overlap. Great for you band students.

Here is a graphic to help keep straight which harmonics are which for the 3 classes of instruments:

Common Misconceptions: (these statements all have errors)

- Waves transport matter.
- Waves do not have energy.
- All waves travel the same way.
- Frequency is connected to loudness for all amplitudes.
- Big waves travel faster than small waves in the same medium.
- Different colors of light are different types of waves.
- Pitch is related to intensity.
- There must be a medium for a wave to travel through.

External Resources

Waves on a string simulator: https://phet.colorado.edu