[thedoc (OP)]

For this week's kitchen science I took some high speed footage of some cello strings but there were some fascinating effects which didn't really fit into the kitchen science, so I thought I would post them here.

 Read more about this experiment.


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

 

[RD]

If you don't mind getting flour/talc on your cello you could try to obtain Chladni patterns...

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http://en.wikipedia.org/wiki/File:Chladni_guitar.png

http://en.wikipedia.org/wiki/Ernst_Chladni#Chladni_plates

[Chemistry4me]

Neat little new Board you've got here. []

[daveshorts]

I had a go at looking for the chaladni patterns directly with the high speed camera but I think the movements were far too small to be visible. My housemate who owns the cello wouldn't be keen on covering it with sand...

[BenV]

I've got a 'spare' acoustic guitar you can test it on...

[RD]

It may be possible to use interferometry to record the minute movements of the cello's surface e.g. reflecting a laser off it, (use a diverging lens to create a cello sized disc of monochromatic light), and record the changing interference patterns on camera...

http://www.wim.ma.htwg-konstanz.de/de/inhalt/50_Studierende/20_Studien-,%20Bachelor%20und%20Projektarbeiten/Poster_Speckle_Interferometrie_Grundler_2.pdf

http://www.h.amu.cz/zvuk/studio/dokumenty/Lit145.pdf

http://en.wikipedia.org/wiki/Laser_Doppler_Vibrometer

(No sand, talc or flour required)

[daveshorts]

Yes a guy I know who does some science lectures called Mark Lewney did a PhD on this subject. However It would require quite a powerful laser to make it work - or I guess a strobed much less powerful laser and a long exposure time.

[RD]

No indication of the power of the laser used on this guitar, (image published 1983)...

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http://books.google.co.uk/books?id=iiCZwwFG0x0C&pg=PA225

[daveshorts]

From Mark Lewney

"
Since you ask about their origin, they were made in the Cardiff Uni
acoustics lab using a powerful green YAG laser (can't remember the exact
power - think it averaged a few kW). In fact, I once blew the power amp
on it: holograms need silence, since if the whole object shakes more than
a quarter wavelength you see diddly squat. The fan on this thing was
making quite a racket, so I muffled it with my coat during exposure, then
remembered to remove it afterwards.

Until the time I forgot. Those big capacitors make a hell of a mess when
they get so hot they explode."