# Wine glass wave lengths

1. Aug 26, 2011

### SugerQueen

1. The problem statement, all variables and given/known data
I calculated some wavelengths for a wine glass I am using in an experiment and they came out in meters just like they should but the wave length out does the diameter of the glass(~9cm) by about 46cm.... Is this ok or is there another way to calculate for a wine glass?

2. Relevant equations

λ =ν/f
and the v being used is 346m/s. ( I am using this because at the time of the eqperiment we didn't think to measure the temp and are just is the speed of sound at 25oC.)

3. The attempt at a solution
Wavelength at the different water levels for glass one:
λ =ν/f λ =ν/f
λ =346/630 λ =346/500
λ =0.55m λ =0.69m

I am only at a very low level of physics so try and keep it relatively simple or I am going to get very lost :) Thank you for any help.

2. Aug 26, 2011

### wukunlin

could you please restate the original question or experiment? I'm not sure how a wine glass has a wavelength.

My guess of your experiment is that either you have detected sound waves from a vibrating wine glass or you have shatter a wine glass at its resonant frequency?
If that is the case then you shouldn't worry about the wavelength of the sound waves being much longer than the size of the glass.

3. Aug 26, 2011

### SugerQueen

Oh sorry,
the experiment is to find out the relationship between the sound produced by running a finger around a wine glass and the frequency of that sound.
Observation: the frequencies of the wineglasses with only a small amount of water decreased very slowly where as lots of water decreased the frequency greatly.
I assumed this is because the bottom part of the wineglass has the stem to reduce the distance the glass can vibrate as well as the level of the water. There is more space for the glass walls to vibrate the further up the water level goes, so the frequency will decrease and the wavelength will increase.
The wavelength is therefore smaller when the water is low, and according to the equation, λ =ν/f the frequency will become larger the smaller the wavelength. Which is why I was doing the calculations to help prove this....
Sorry if that doesn't make sense......

4. Aug 27, 2011

### wukunlin

oh ok, I get what is going on now.

There is nothing wrong in your calculations at all.
I suggest having another look at your assumption

5. Aug 27, 2011

### PeterO

The wavelength of the sound produced by a guitar string doesn't have to relate to the string - otherwise tightening the string wouldn't do anything??

The size of the glass vs the frequency at which it vibrates need not also be directly related.

Having said that, if you could put a strobe light on the vibrating glass, you would probably be looking at the circumference of the glass if anything - not that that determines the frequency either.

6. Aug 27, 2011

### SugerQueen

Alright thank you :)

7. Aug 27, 2011

### PeterO

It is only in "sound producers" that are based on an air column, that the frequencey of the sound in the air is related to a dimension of the "sound producer".
eg: flute, trumpet, organ, clarinet, oboe, ...

8. Aug 27, 2011

### SugerQueen

oh and thank you for the strobe light idea although I don't have one to try the idea out I can still use it as an improvement/ follow on experiment :)

9. Aug 27, 2011

### SugerQueen

The persons finger slides and sticks along the surface of the glass as they trace it around the rim. This passes energy on to the glass and the glass resonates. The vibrating glass forces air molecules to vibrate at the same frequency as the glass and therefore produce the sound waves that can be heard by listeners. When water is added to the glass the sound herd is sometimes very different to the original sound made. As the sound waves/air moves around the glass, they move the water molecules as well, creating a tremor of water which is visible to the human eye at the edge of the glass. The dragging water molecules increase the mass of the glass as an object and therefore reduce the energy of the wave traveling through the glass as the energy is taken when forcing the water to move. When the energy is reduced, the frequency of the wave in the glass are also lowered, this is then reflected in the pitch of the sound wave that can be heard?

Is this explanation any better then the one above? or am I still not on the right track?

10. Aug 27, 2011

### PeterO

Look at this.

Last edited by a moderator: Sep 25, 2014
11. Aug 27, 2011

### wukunlin

that sounds like what I would say if i'm writing a report for that experiment, so I would say you are on the right track