I am looking to replicate this eperiment

[Bluehat]

Hello everyone,

 

I am looking to replicate this experiment with my Dad as a project for the summer vacation:

 

WMV Movie File of the epxeriment

 

this experiment seems to be extremely cool!

i am especialy intrested in the 'fingers' created during the end.

 

it shows the apperance of Faraday Waves in cornstarch.

 

i have several questions:

-in the video the there are some variables:

f=120 Hz

a=25g (it goes from 0 to 25 along the video)

what do these variables mean?

 

i am guessing that the cornstarch is being shaked by some device that shakes it up and down, am i right?

 

where can i get such a device? is this an example of what i'm looking for?

 

also, here is a link i found for a PDF File which details some of the aspects of the experiment (though i still dont understand some stuff....)

Thanks!

BlueHat

[LucidDreamer]

That's a cool video. The f is frequency of the waves formed, which is the amount of waves that you generate per time. The a is the acceleration that the machine uses to create the waves. g is the acceleration of gravity which is 32 ft/s, so 25 g would be an acceleration equal to 25 times gravity. Acceleration is the increase in the amount of speed per time.

 

Yes the cornstarch is being shaken.

 

Yes those machines look like they might do the trick but don't go buy one on my advice.

 

Maybe there is another way you could create the waves without having to buy one of those machines. The only way I can think of right now is to borrow a paint shaker and try to modify it for your use. But I have no idea if that would work. Maybe someone else has some more info on this experiment or maybe they could suggest another way to create the waves without buying a machine.

[MolecularMan14]

Wow, if you replicate this experiment, let me know how it goes! Looks sweet!

[Bluehat]

Thanks guys!

 

you can bet i'll post how it goes on when i'm done!!

 

anyway, my dad suggested that i use my sounds system speaker, connected to my computer, which is running a sound generating program called sinusoid (by gemtree.com) where you can control the frequency of the sound.

 

i have tried the program through my sound system speakers, and the speaker is powerful enough to shake my hand pretty hard, so i think it's ok....

 

now, with the speaker , F is still F, but now A is Volume, right?

 

the louder the speaker the more force will be exerted on the plate, right?

 

Thanks guys!

i'm gonna buy some cornstarch now!

 

-BlueHat

[Bluehat]

okey, i got the corn starch, added water stirred, put it on the speker which was playing a 120 hz tone at MAX volume (can you say annoying?).

and....... nothing happpend.

 

i removed the casing and put the bowl directly on the cone, and still nothing happend.....

 

any ideas what to do now?

 

some notes:

-i didnt use a bowl shaped like a petri dish, it was shaped more like a cone (like a normal bowl)

 

it seems that i need to find a way to connect the bowl to the vibrating surface of the speaker, without harming it, any ideas?

[LucidDreamer]

hmm, I think a pie plate might work better than a bowl. I believe A is still acceleration; you just dont know what it is now without a machine that automatically measures it. I'm not sure how to make the speaker work better. Maybe you can attach it to a larger speaker with tape.

[Bluehat]

New Results:

 

I went to the local car shop, and got a free (100)Watt, (4)Ohm speaker.

 

this time i placed a bowl with a flat bottom (like a pie plate ).

 

 

when i fill it with 0.5 cm of water, at 120hz the faraday waves are clearly visible .

 

but.... when i put about 0.5 cm of (liquid) cornstarch, nothing happens..........

 

i'm thinking that because the density of the cornstarch, the current volume is not loud enough to make the waves in it.

 

could someone please explain some more about the acceleration part?

 

at the moment i'm imagining a surface (of the shaker) that is shaking 120 times a second (120 hz) and the farther the surface travels at each vibration, the higher the acceleration.

 

am i correct?

(if i am i'm almost certain that this translates into volume with speakers)

[mossoi]

The volume of the sound increases as the displacement of the cone increases. So, yes, a higher volume means faster acceleration as the cone is moving further at the same frequency.

 

Have you got the mix of corn starch to water correct? This looks to me like the holes and fingers effect is due to the thixotropic properties of the corn starch solution.

 

If you need more volume you can always pass the output of the PC through a hifi amp to step it up.

[Bluehat]

actualy i am putting through a hifi system, otherwise the volume is terribly low...

 

 

maybe i need a better one (i was using the standerd pc speakers that come with the pc as an amplifier )

 

Thanks!

[mossoi]

Have you got the right speaker for the frequency you are playing? I'm not too technical when it comes to this but obviously there is an optimal radius of cone for certain frequency ranges which will allow maximum acceleration.

[arydberg]

Sorry it was a solution of water and cornstarch.

[Guest gematt]

Stick a piezoelectric buzzer in the fluid.