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

1. Mar 22, 2013

### 06mangro

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

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

2. Mar 22, 2013

### Staff: Mentor

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

3. Mar 22, 2013

### 06mangro

4. Mar 22, 2013

### Staff: Mentor

... and what?

5. Mar 22, 2013

### TSny

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

Last edited by a moderator: Sep 25, 2014
6. Mar 22, 2013

### 06mangro

yes that is what im 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 wont but is that affectively what is happening ?

Thanks

7. Mar 22, 2013

### Staff: Mentor

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.

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 frequency