What Unique Variables Can Affect the Resonant Frequency in a Physics Experiment?

[asu04]

Hi all.

I am planning to do an IB extended essay on physics but unfortunately I am having some problems with coming up with a good research question that will allow me to conduct an experiment with high school equipment but involve theory and maths at the IB level. Originally, I intended to do the following research question:

An investigation in the relationship between the depth of water in a wineglass and the resonant frequency of the glass

However, after consulting my teacher, I found out that this topic is too common, and we actually conduct the investigation anyway in an internal assessment.

I would still like to do a question on resonance but the issue now is identifying a good independent variable that allows me to approach the topic in a more unique angle. Are their any other variables (preferably quantifiable) that I can alter and investigate that would affect the resonant frequency? I'm looking more for a nudge in the right direction rather than an explicit explanation.

Thanks in advance for any help

 

[Stonebridge]

Welcome to Physics Forums.
There is a very interesting experiment involving a cup/mug with a handle.
here
http://www.physics.umd.edu/lecdem/services/demos/demosh3/h3-62.htm
How about investigating what's going on here and what factor or factors affect the difference in the two resonant frequencies.
There is certainly something that can be quantified that might be causing this.

 

[asu04]

Hmmm this experiment is exactly the kind of thing I'm looking for and plus since its got two resonant frequencies I can even possibly explore the relationship between the two and any independent variable I'm changing.

Thanks for the suggestion :D

problem is now though I have to identify one variable that I'm going to be changing (as IB really stresses that a focussed specific topic is a good one!) and I'm not really sure what variable(s) could cause a change. I supposed I could change the thickness of the mug (hence the 'spring constant' of the mug) and alter it that way but I'd be hard pressed to find a mug that's the same material, tallness and width with the same type of handle but a different thickness at the rim.

Would changing the density of a liquid I put in there have a significant effect on the resonant frequency? In theory some of the liquid inside gets dragged along and hence decreases the frequency of the resonance right? If I changed the density of some liquid inside, would that cause a significant enough change in the mass that the oscillations of the rim drag around?

 

[Stonebridge]

First you need to identify why there are two different frequencies, and the quantity that is causing the lower one. Another clue I would give is that there is no need to add water or any liquid to the cup to investigate this. You could also do this with just one mug.
What do you suppose the significance of the handle is?

 

[asu04]

Hmm i understand that the lower frequency is produced when the handle coincides with the antinode of the standing wave produced hence increasing the mass vibrating and reducing the frequency. But at most, the very same coffee mug will only produce 2 different resonant frequencies right? If I hit the cup at, say, at a 4 o clock position with 12 o clock being the handle, does the mass of the handle still have an effect on the frequency produced? If it doesn't, then I don't think I can generate enough data to analyze for the IB...D: (if I only use one mug that is)

 

[asu04]

Hmmm unless i change the mass of the handle by say, sticking blu tak on to it?

 

[Stonebridge]

Good idea.
Yes, it's when the handle is at an antinode (there are 4 antinodes equispaced around the rim) that you get the lower frequency. When the handle is at a node it has little or no effect.
You could also use a mug with no handle of its own, and create a mass of blutak or something stuck or clamped to the side near the top.
The main experimental concern I imagine, will be accurately measuring the two resonant frequencies.
In the video clip on the web page link, the difference is about a semitone.
The aim would be, as you say, to investigate the effect of changing the mass of the "handle".

You need to discuss this with your teacher to see if it looks possible to do this successfully.