Why do all wine glass have four nodes (4th harmonic)?

[06mangro]

Why do all wine glass have four nodes (4th harmonic)??

Why do wine glass have four nodes... or four anitnodes... (4th harmonic)?

 

[mfb]

Every circular thing has a 4th harmonic, I think, together with many other modes. Why do you expect any difference for wine glasses?

 

[06mangro]

http://infoscience.epfl.ch/record/112607/files/poster.pdf

 

[mfb]

... and what?

 

[TSny]

o6mangro, are you asking "why does the fundamental mode have 4 nodes" (as shown here )?

 

[06mangro]

yes that is what I am talking about!
you got it!
Why is it that wine glasses have four nodes on fundamental frequency?

and also does the fundamental frequency of the object (wine glass + water) change when water level is changed.

The actual wine glass' fundamental frequency won't but is that affectively what is happening ?

Thanks

 

[mfb]

Ah, that question makes more sense.
The "easiest" oscillation which keeps the length of the ring of the glass constant* is a compression in one direction, and an expansion in the other one. This leads to 4 nodes and 4 anti-nodes.

and also does the fundamental frequency of the object (wine glass + water) change when water level is changed.

If the glass has to move more water in the oscillation, it needs more time for the same displacement (at the same elongation => same force).

*changing the length would need much more force, and give a higher frequencyCan we restrict the discussion to one thread instead of two, please?