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Old Oct 24th 2013, 06:42 PM   #1
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Steel balls vibration

When steel balls are touched lightly, they produce a chirping sound, we are to consider why this happens.
We have come up with 3 ideas:
1)it is influenced by the curvature of the ball and the sound waves passing through the balls
2)it is the hand/ball interface that creates chirp
3) chirp is influenced by the region of air above and below the ball
We are unsure which it could be and would like some help.
Any ideas?
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Old Oct 25th 2013, 08:13 AM   #2
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Originally Posted by jijilulu View Post
When steel balls are touched lightly, they produce a chirping sound, we are to consider why this happens.
We have come up with 3 ideas:
1)it is influenced by the curvature of the ball and the sound waves passing through the balls
2)it is the hand/ball interface that creates chirp
3) chirp is influenced by the region of air above and below the ball
We are unsure which it could be and would like some help.
Any ideas?
Put any two rigid surfaces together and you will get some kind of "click" sound, so your chirp is going to be when you put the two metal surfaces together. I would think that the two balls will bounce off each other and then be put right back together by the force the hands are exerting, causing quick series of clicks which makes your chirp.

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Old Oct 25th 2013, 10:47 PM   #3
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We have to consider why it occurs to perfectly spherical balls, yet why it does not occur with cubes and why it occurs to varying degrees between shapes - such as ellipsoids. Any ideas?
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Old Oct 30th 2013, 11:22 AM   #4
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Just a Guess

I would suggest that this might be due to the size of the contact area
and with the change in contact area due to small changes in relative position of the objects.

I am guessing that cubes touching face to face dont exhibit this phenomenon,
What about cubes touching corner to corner, or corner to face?

What about spheres touching cubes?
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Old Oct 30th 2013, 11:35 AM   #5
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Am I misinterpreting?

I have just re-read your original post,
It does not actually mention more than one ball...

If you are describing a situation with only a single ball,
then this could be similar to making a wine glass sing by running a finger round the rim...

We are then talking about a resonance,
The sound wave moves around the object and meets itself coming back!
If the frequency is just right then the sound waves will reinforce and just the lightest touch will produce a surprisingly loud sound.

Setting up resonance in a sphere is easier than in other shapes.
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Old Oct 30th 2013, 05:00 PM   #6
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I apologise for that, the experiment does indeed concern two balls
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Old Dec 25th 2013, 06:31 PM   #7
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you should attempt looking up the physics of the chirping sound itself- a chirp is a sound of which the frequency increases over time resulting in a change in pitch. If it is a characteristic of the steel balls you might want to check out how the sound waves created by the balls' contact interact with their spherical forms.
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Old Feb 10th 2014, 09:52 PM   #8
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Im wondering whether the chirp may be produced due to elastic interactions between the balls (Restitution coefficient Is high). Could this create the high pitched chirp heard? If so, why do spheres produce this particularly well?
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Old Feb 11th 2014, 11:19 AM   #9
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Sounds Plausible?

I am still supporting a resonance idea.

If one were to watch at the balls in super slow-motion (under high magnification) one would see the balls flexing in quite clearly defined modes.
For example (relatively) tall and thin moving to (relatively) short and fat and back again.
(note the actual movement will be tiny)

As each ball flexes, the contact points will perhaps come apart, then meet again.
This will happen in concert with the resonant frequency, tending to reinforce it.

Note that I have no idea if this is correct, but it seems plausible to me.
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