## Due 3:30 pm, Tuesday, December 8th

Physics 105, Fall Term, 2009

Did you complete the reading assignment?

Yes
No

## KEY CONCEPTS:

1) Sound is nothing more than waves with frequencies in the audible range of hearing.

2) Resonance occurs when an object oscillates at its natural frequency.

Exercise 1

You will need to have the audio on for this applet to complete the following activity. Go to: http://phet.colorado.edu/sims/sound/sound_en.jnlp. Select the 'Listener' bubble on the right side of the applet so that you will hear whatever the woman on the screen is "hearing". Turn the volume on your computer/speakers to low and then click the 'Audio Enabled' checkbox on the right side of the applet.

Decrease the frequency by using the scrollbar in the upper right of the applet. What is the frequency of sound wave synonymous to?

Volume
Pitch
Tempo

Increase the Amplitude by using the scrollbar in the upper right of the applet. What is the amplitude of a sound wave synonymous to?

Volume
Pitch
Tempo

Now click on the two source interference tab at the top of the applet. Select the 'Listener' and 'Audio Enabled' options from the right side of the screen again. Drag the listener straight up and down on the screen with the mouse. You should be hearing different levels of volume. Now compare three spots on the straight line that you picked where: 1. There is no checker pattern, 2. The black and white checker squares pass by, and 3. the gray, horizontal-ish lines between the checker squares.

Rank the volume of the different spots from loudest to quietest:

Not checkered, checkered, lines
Checkered, lines, not checkered
Lines, not checkered, checkered
Not checkered, lines, checkered
Checkered, not checkered, lines
Lines, checkered, not checkered

What is happening at each of these spots? How do you know this?

## Exercise 2

Anyone who watched cartoons as a child knows that opera singers can break crystal glasses by singing. This is a result of a crystal glass resonating because it is being excited by a frequency that is equal to the glasses natural frequency. Here is a slow motion video of this real life phenomena (minus the opera singer), but you can see how the vibrations causes the glass to shatter: http://www.acoustics.salford.ac.uk/feschools/waves/wine1video.htmm

How can you notice when an object is resonating?

FEEDBACK

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Was there anything that you didn't understand in the reading assignment?  What was confusing to you?