# INTRO TO PHYSICS: Impedence, pitch, vibration, reasonance

1. Oct 3, 2006

### Dunkaroos

EASY STUFF: Impedence, pitch, vibration, reasonance... Please Help!

I would really appreciate it if you guys could take a look at these problems I have difficulty with. Thanks a lot. My answers are in red.

1. As impedance decreases, frequency decreases?

2. For the vibration spectrum (of frequency and amplitude) of a plucked spring, why are there spaces between the lines? Why are most frequencies zero amplitude?

3. After playing a long peice of music, the pitch of the string in a violin will be lower
Why does the pitch change?
What can you do to adjust the violin so it plays the correct pitch?

4. Why does our voice sound different when we have a cold? Sinuses are stuffed. But how can this be explained by physics?

5. Identify if the following situations are Forced Vibration or Reasonance:
1. The sounding board of a piano makes the sound louder. forced
2. A piano strikes a chord and breaks a dish in the next room. resonance
3. One barking dog causes the doorbell to ring, but another does not. resonance
4. An earthquake can cause the dishes onn your shelves to vibrate. forced
5. Sometimes, if the wind instruments hit a particular note, the snare (a metal attachment) on the snare drum will begin to hum. forced

6. In a flight, you can permanently deafen someone by hitting both of his ears simultaneously with your open hands. Explain.

Last edited: Oct 3, 2006
2. Oct 3, 2006

### Dunkaroos

No one? :uhh:

no need to answer all

every little bit would be appreciated

thanks.

3. Oct 4, 2006

### edavey8205

1. Is correct - Impendanace and frequency are directly related

4. Your voice sounds different because your vocal cords swell changing the vibractions. http://www.entnet.org/healthinfo/throat/Your_voice.cfm [Broken] Found that to be pretty interesting if you would like to know more about the subject.

Last edited by a moderator: May 2, 2017
4. Oct 4, 2006

### Dunkaroos

About #1...

Let Impedance =Z
p==pressure
v=velocity

Z = p/v and v=f(lamda)

So Z= p / (f(lamda))

Isn't Impedance inversely proportional to frequency?

Last edited: Oct 4, 2006
5. Oct 5, 2006

### Dunkaroos

bumpy bump bump

6. Oct 5, 2006

### Galileo

If the string (or spring?) is fixed at both ends it can't vibrate in any old way, but only in a linear combination of eigenmodes with frequencies that are integer multiples of some fundamental frequency.

Last edited: Oct 5, 2006
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