Cornstarch Monsters - Non-Newtonian shear-thickening fluid in a speaker cone

Non-Newtonian shear-thickening fluid in a speaker cone subjected to periodic forcing. This was the first test and is just a preliminary video - better one(s) to come. The speaker was an 800W Mutant 30cm dia. subwoofer (£24). The sound box was a sealed enclosure at optimum volume (as given in manual) made by myself out of 15mm MDF, glued (butt-join), sealed and screwed together. The speaker was connected to a signal generator passed through a 12dB power amplifier. An oscilloscope was put in line to check the power going to the speaker (knowing its impedance is 4ohms). The frequency was around 50Hz and the power was somewhere in the range 75-100W (so an 800W subwoofer was overkill, hehe). I was so pre-occupied trying to stop all the equipment shaking itself off the table that I didn't record the actual power ;-( - something to get right next time. I started it at 250W and that made a great mess! The tiny microphone on my camera does no justice to the loudness of the sine wave at 100W! The video is so short thanks to my old memory stick having low capacity at high quality ;-(

As for the fluid, pure cornstarch (a.k.a. cornflour in the USA) with cold tap water mixed at a mass ratio 1 part water to 1.25 parts cornstarch. You can start to notice the shear thickening (Non-Newtonian) effect at 1:1 mass ratio. The harder you stir it, the more it resists you exponentially. This experiment actually had 100g of water in the cone, so that required 125g of cornstarch.

A non-Newtonian fluid is simply classed as one whose stress / strain-rate curve is not linear. In one dimension, a Newtonian fluid obeys the relationship tau = mu * dU/dy. tau is the stress, mu the viscosity and dU/dy the local velocity gradient (or strain rate by units 1/s). In 3D the stress tensor is given by [tau] = mu * (grad(U) + grad(U)_transpose). A non-Newtonian fluid may have higher order velocity derivatives, power laws and even temporal terms (i.e. a thixotropic fluid has time-varying viscosity where the viscosity reduces under continued constant rate of shear). Paint is made to be shear thinning so it does not run down vertical walls once applied.

Category:

Education

Tags:

• Cornstarch
• Non-Newtonian
• Shear-thickening
• speaker
• fluid

[ohheycrystalhey]

How exactly did you create the soundbox? Do you need it for this particular experiment? I'm trying to do this for a school project but I'm not sure how.

[khyar]

@ohheycrystalhey Hi, I used 15mm thick MDF board and PVA wood glue + nails. I cut the wood on a band saw and used simple butt-joins. It is just a simple empty box with optimal internal volume for bass resonance (the volume was given in the instruction manual). For the top part I used a jigsaw to cut the round hole for the speaker to sit in and then screwed the speaker into it. This part was screwed and silicone-sealed on to the box in case I ever needed to get inside.

[khyar]

@ohheycrystalhey The sound box is not absolutely necessary, although you get FAR louder sound! What is necessary is some way of holding the speaker still otherwise it will shake itself off the table! Also, this particular speaker has a plastic cone with butyl rubber lips and is sealed, so there is no need to cover it with anything. I see some commenters are worried about this - the speaker is still working just as new, just wipe it dry after the experiment.

[whymewhyherewhynow]

Being a mom, the first thing I thought was "Oh my god, the speakers! Put some plastic wrap on it first!"

[tjigg1]

Is it wrong if I say I want to eat it?

[EliCross]

Looks like albino wrestling.

[TehlioNN]

IT'S ALIVE

[standalonefighter]

rofl it looks like a spider is coming out that white stuff and trying to escape xD

[AceSpade09]

its like the dancefloor of a nightclub

[dMATTYb]

flubber

[MrGouwenaar]

IT'S ALIVE!!

[ShyFx8]

cool .. try to make mudshake?  :p