Module 8—Mechanical Waves

Module Summary

 

In this module you looked for answers to these questions:

In this module you learned that a mechanical wave requires a medium, a source that disturbs the medium, and a way for adjacent parts of the medium to influence each other. Along with this, you saw that characteristics of waves, such as speed, frequency, wavelength, and amplitude, are needed to describe wave motion. Three of these characteristics are related by the universal wave equation,

 

You studied how waves interact with barriers or boundaries; and through this, you can better understand how satellite dishes concentrate signals. You learned that θincident = θreflected when waves reflect. As well, you saw how the Huygens’ Principle can help explain reflection.

 

You learned about constructive and destructive interference. You saw how waves can be combined and that the result changes as the phases of the waves change. You used the principle of superposition to combine waves. You studied standing waves and how the nodes of standing waves are distributed in vibrating strings half a wavelength apart.

 

You also studied how air columns resonate and how the wavelength and air column lengths are related. For a closed-air column to resonate, its length must be an odd multiple of a quarter of the standing wave’s length For an open-air column to resonate, the length must be a multiple of half of the standing wave’s length

 

You continued studying about wave interference, expanding your knowledge to include multiple sources of waves. You learned conditions that allow for nodal and antinodal lines to occur. The following table summarizes how the wavelength and the path length difference lead to constructive or destructive interference.

 

Constructive Interference

Destructive Interference

 

You also learned about the result of a moving sound source and how this Doppler effect changes what a stationary observer hears. The Doppler effect is the observed change in frequency and wavelength of a wave produced by a moving source relative to an observer. Expressed as an equation, it is

 

     

 

Quantity

Symbol

SI Unit

Doppler frequency (observed)

fd

Hz

source frequency

fs

Hz

wave velocity

vw

m/s

source velocity

vs

m/s

 

The wave and source velocities are subtracted when the source is moving towards the stationary observer. The velocities are added when the source is moving away from the stationary observer.

 

Module 8 Assessment


The assessment for Module 8 consists of six (6) assignments: