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Amazing cornstarch speaker monster: Not as easy as it looks

Who knew that cornstarch can be used for so much more than just a decent lemon meringue pie? This science demonstration is just so cool that I rushed home to try it myself.

The video above shows the reaction of a cornstarch paste on a speaker with a steady tone applied to it. My photos below show how to make a complete mess of a kitchen and home theater, with absolutely zero results. I mixed up the cornstarch paste, found a speaker I didn't mind destroying, and set out to make magic. I tried to protect the speaker at first, so I stuck the speaker inside a baggie. No reaction at all, no matter what what signal I played or the volume. I started with a little portable player, but quickly moved onto a real amplifier. I ended up sacrificing the speaker after all and poured the paste directly onto the driver. Again, no movement of the paste. I needed more power, and an oscillator to generate lower frequencies.

Finally, I didn't want to destroy my subwoofer driver, but I put the paste on top of the sub's enclosure and blasted it as loud as I think the foundation of my home could withstand. Alas, the paste just sat there, taunting me with its stillness.

Go ahead and watch the video again. Lord knows that's the only way I'm going to see magical dancing cornstarch. If you get it to work, let me know your secret.






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(8) Comments

152iq:
As a "non-newtonian" liquid, the corn starch liquid acts solid when impacted directly. A sound wave in the air has ...More »


Comments

By Reverend at 12:23 PM ON 02/05/09

Given the texture of the cornstarch mix I think the most important part of this is not only the steady tone but also him breaking up the initial form of the paste at the beginning of the video. For example you can roll it into a ball in your hand, and as long as you keep rolling it its solid state remains. As soon as the motion stops it turns back into a liquid. So with the constant tone it will take on the form of the subwoofer in a solid state until it is broken up by the stick and forced to try to find a new form… Just a thought… Otherwise it may have just been too thick.

By StuckOnStupid at 1:28 PM ON 02/05/09

If i understand the properties of the past right, made in a big enough batch you can actually run across the surface. But if you stop you sink, so that being said the past is going to act like a solid and just transfer the sound or vibrations straight through it. you might, like the Reverand mentioned, just not make it so thick next time.

By jmp478 at 2:58 PM ON 02/05/09

You obviously understand the properties of spam, as well...

By CJ at 3:23 PM ON 02/05/09

There was an episode of Mythbusters where they walked on a water/corn starch mixture.

The good Reverend is likely correct, you need to break it up. The frequency probably isn't important, walking would be very low frequency.

By Felipe 058 at 3:58 PM ON 02/05/09

The substance in the video seems to be more the consistency of silly putty rather than a thick paste. The mixture you made and photographed looks more the consistency of a thick paste, similar to toothpaste but not quite as thick.

By kamisama at 5:09 PM ON 02/05/09

I have done this for open day (I am a science teacher) and I confirm it works. You need to get the mixture to a point where you can pick a bit out of it and roll it into a ball with your hands, and then put it on a table and watch it turn into liquid again. You should be able to stir it slowly, but not quickly.

Then you need a speaker. Any should work really, bearing in mind the next bit: You need to produce a constant low-frequency sound. We had something at school that did the job, but I don't know how you'd produce it at home. Maybe connect the speaker to a PC and use a sound editing program...

Anyway, I put cling-film over the speaker and poured the cornstarch directly into it and it worked fine. When you find the right frequency (you need to be able to vary the frequency) the fingers will climb out of the goo on their own. It is quite a sight. You can pick one off and it'll melt in your fingers. Once they get going you can change the frequency to change the behaviour of the fingers.

By Dalhimar at 5:32 PM ON 02/05/09

Ok for you folks i will explain this.
The cornstarch when mixed with "SMALL" amounts of water will create a STF, or shear thickening fluid. This is a special type of fluid that when stressed will actually harden. This is because when the molecules are stressed in this fluid like state they realign themselves to a rigid and sometimes crystaline structure depending on the materials added. This is actually being used in some experimental Kevlar armor to reduce the amount of damage per layer of kevlar.
Think of sillyputty, you can mold it but if you yank hard it actually breaks instead of flowing. or go throw it on a hard cold surface, it can explode.
Now to get this to work right you need to have it so you can stick your finger in slowly but if you tap the fluid, your finger will not enter. This should be about the right consistency to work.

By 152iq at 9:47 AM ON 02/06/09

As a "non-newtonian" liquid, the corn starch liquid acts solid when impacted directly. A sound wave in the air has not enough energy to affect change, which is why in the video the goop is placed on the speaker cone itself.

One optical illusion of the video that is hard to identify is the motion of the speaker. The cone is moving fully three fourths of an inch. "no it's not", you say. The sound wave is at 60 hertz which is very near the frame rate of 59.94 fields per second of NTSC video. This means that the cone movement is being captured in nearly the same position in every frame. You can only perceive a shift in the position of the speaker over a couple seconds. It is most noticeable at the end when the speaker stops moving and returns to rest. That violent interaction is why it works.


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