Chapter 11: Waves and Sound

Lesson 3: Sound Waves

Objectives:

When you have completed this lesson and the homework, you will be able to:

  • understand that sounds waves are mechanical, longitudinal waves which require a material medium in which to travel

  • understand the meanings of the terms pitch, frequency, intensity and decibel scale

  • know the speed of sound in air and how this speed varies as the media changes

  • understand how sound waves can interfere and be able to explain the phenomena of beats.

  • understand the concept of the Doppler effect and how it is related to the relative motion of the source of the sound waves.

  • explain the phenomena of natural frequency and the associated concept of resonance

In this lesson we will address the following standard from the Indiana Academic Standards for Physics I: 

P.1.22

Describe waves in terms of their fundamental characteristics of velocity, wavelength, frequency or period, and amplitude. Know that radio waves, light, and X-rays are different wavelength bands in the spectrum of electromagnetic waves, whose speed in a vacuum is approximately 3 108 m/s (186,000 miles/second).

 

The Lesson

An excellent online lesson on this topic is presented by the Physics Classroom website.  Follow this link to see that lesson.  You should complete Lessons 1 and 2.  Each lesson has several parts, so this will take a bit of time, but the material is good and easy to understand.   Take notes as you go. Pay attention to the conceptual questions that appear on the bottom of the each section ... you will see some of those again in the near future.

http://www.physicsclassroom.com/Class/sound/soundtoc.html

Make sure you .....

  • understand that sounds waves are mechanical, longitudinal waves which require a material medium in which to travel

  • understand the meanings of the terms pitch, frequency, intensity and decibel scale

  • know the speed of sound in air and how this speed varies as the media changes

  • understand how sound waves can interfere and be able to explain the phenomena of beats.

  • understand the concept of the Doppler effect and how it is related to the relative motion of the source of the sound waves.

  • explain the phenomena of natural frequency and the associated concept of resonance

Here are some sites to check out to help you visualize these concepts

Doppler Effect
Beat Frequencies A very nice explanation, along with a demo where you can actually hear the beat frequencies: http://www.school-for-champions.com/science/soundbeat.htm

Scroll down for the demo that you can hear.

Interference of Sound Waves http://www.phy.ntnu.edu.tw/ntnujava/viewtopic.php?t=35
Sonic Boom When the source of the sound moves faster than the sound waves, you get a sonic boom. To show this, go here http://www.phy.ntnu.edu.tw/java/Doppler/Doppler.html and use your mouse to drag the little arrow for source speed so that it is greater than the wave speed (like 85 or so). Then click start and see what happens when the jet moves faster than sound.
   

For another example of the Doppler effect, follow this link:
http://home.a-city.de/walter.fendt/phe/dopplereff.htm

For more about beats. here are two links to follow
http://members.nbci.com/Surendranath/Beats/Beats.html

There are no problems on this section, just some conceptual questions on the exam.


This is the end of the lesson. You can return to the unit main page.

 

 

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(c) 2003 Mark Blachly
Indiana Online Academy
 

This page was last updated
03.22.2004