Did you complete the reading assignment?
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.
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
Decrease the frequency by using the scrollbar in the upper right of the
applet. What is the frequency of sound wave synonymous to?
Increase the Amplitude by using the scrollbar in the upper right of the applet.
What is the amplitude of a sound wave synonymous to?
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?
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:
How can you notice when an object is resonating?
The comments entered in these last two boxes go into a big anonymous data file that I will use to guide the lectures of the day. That means two things:
1) If you have a specific question or concern and would like an individual
answer you will need to come by the office or send an email.
2) If you really want to get an anonymous comment to me before the lecture, it
must be submitted before 11am that day.
Was there anything that you didn't understand in the reading assignment?
What was confusing to you?