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On the Lighter Side => Science Experiments => Topic started by: thedoc on 13/07/2010 14:44:24

Title: Acoustic Levitation - Garage Science
Post by: thedoc on 13/07/2010 14:44:24

Here is an interesting effect I noticed a couple of years ago. I was actually attempting to smash a wineglass using sound. I was using a piece of paper to detect when the glass was nearing resonance, and accidentally discovered something altogether more fascinating, the paper started to levitate.

 Read more about this experiment. (http://www.thenakedscientists.com/HTML/content/kitchenscience/garage-science/exp/acoustic-levitation/)


Garage science is a blog of science experiments you probably can't or shouldn't do at home

 

Title: Acoustic Levitation - Garage Science
Post by: LeeE on 23/02/2009 21:37:20

Interesting.  I don't think that thinking of air rushing in and out of the glass is the answer though.  The only air that will be moving in to and out of the glass will just be the air in the immediate vicinity of the mouth of the glass; I don't think there'll be any air-flow, as such, and the air movement will be more like that of A.C. current rather than D.C. current.  Resonation is certainly playing some part though, whether it be the glass putting energy in to the air, and in turn, in to the piece of paper, or whether the air is resonating directly.

The first thing that comes to my mind is that you're setting up standing waves in the air column within the glass that aren't perfectly tuned and so advance up the column.  That's just a guess though.

It would have been interesting to have had a small ball-bearing in the glass too - that would have given a good indication of the glass resonating but wouldn't react to the air resonating very much.

Title: Acoustic Levitation - Garage Science
Post by: daveshorts on 24/02/2009 10:28:38

I am not saying that there is any net air flow, just that something which is more dense than the air will feel a net force because it can move.
Chaldni plates (http://www.physics.ucla.edu/demoweb/demomanual/acoustics/effects_of_sound/chladni_plate.html) move sand around because the antinodes are moving more than the nodes, so a particle of sand will bounce a long way at an antinode but not move at a node, and so it will tend to move down the gradient of amplitude.

Another explanation I have heard is that it is waves reflecting off the piece of paper, which I think may be equivalent.

The glass was definitely not resonating, I managed to get glasses resonating nicely later, and that was a very different effect, and didn't make the paper float.

Title: Acoustic Levitation - Garage Science
Post by: lyner on 24/02/2009 21:07:41

This is just a demonstration of the fact that there is no such thing as 'suck'.
It happens all the time with powerful loudspeakers. When the cone moves forwards, the air is actually pushed forwards by the cone. The air molecules are actually given momentum in a forward direction by impacts with the cone. When the cone moves backwards, air rushes in from a whole hemisphere due to the reduced pressure. This generates a net flow of air at right angles to the cone and in from the sides. You can see a candle flame 'pushed' outwards.
The glass in the experiment behaves in just the same way.

Title: None
Post by: opus on 24/06/2009 08:54:52

just look up Acoustic Levitation on Youtube - you'll find a lot more.  this technique is already being used in silicon wafer manufacturing.

Title: None
Post by: Dr. David Deak on 16/12/2009 14:56:48

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