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Styrofoam Slide (May 2015)

Posted May 01, 2015 12:00 AM
Pathfinder Tags: challenge question

This month's Challenge Question: Specs & Techs from IHS Engineering360:

Try this experiment: slide a Styrofoam cup full of water across a smooth (finished) wood surface. Make sure the speed is around 10 cm/s. You will notice that at this speed droplets of water from the cup shoot up to about 20 cm. Explain why.

And the answer is:

As you slide the cup at this speed, energy couples into the sliding cup. The almost-flat bottom of the cup slips and sticks to the surface, producing nonlinear vibrations. This is exactly a relaxation oscillator (producing a non-sinusoidal repetitive signal) that immediately produces standing waves in the surface of water. As you continue pushing the cup the water crests of the standing wave increase in height, causing drops of water to break from the surface and be projected into the air.

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#1

Re: Styrofoam Slide (May 2015)

05/01/2015 2:38 AM

I suppose it is vibration sound created by movement of the uneven surface of the cup which result in standing and conflicting waves at the surface. The Same effect would be seen if the cup is placed on a vibrating table and the frequency is varied.

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#2
In reply to #1

Re: Styrofoam Slide (May 2015)

05/01/2015 3:01 AM

I have noticed the same effect on a CNC router where the combining and opposing sounds created by the router and the independent X and Y steppers produce a resultant sound and varying patterns on a cup of coffee placed on the cutting table. Most noticeable when cutting curves or circles.

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#3

Re: Styrofoam Slide (May 2015)

05/01/2015 6:48 AM

Resonant frequency.

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#4

Re: Styrofoam Slide (May 2015)

05/01/2015 7:29 PM
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#5
In reply to #4

Re: Styrofoam Slide (May 2015)

05/01/2015 10:23 PM

Chinese have a 'dancing bowl' (or some other name) - when you rub your hands around the rim, the water can put on quite a spectacular performance.

Resonances, standing waves, etc etc -

Some tricks to it, tho -

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#7
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Re: Styrofoam Slide (May 2015)

05/02/2015 2:36 AM
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#6

Re: Styrofoam Slide (May 2015)

05/02/2015 1:17 AM

From Wiki :- Styrofoam is a trademarked brand of closed-cell extruded polystyrene foam currently made for thermal insulation and craft applications. It is owned and manufactured by The Dow Chemical Company.[1]

In the United States and Canada, the word styrofoam incorrectly refers to expanded (not extruded) polystyrene foam, such as disposable coffee cups, coolers, or cushioning material in packaging, which is typically white and is made of expanded polystyrene beads.[1] The term is used generically although it is a different material from the extruded polystyrene used for Styrofoam insulation. The Styrofoam brand polystyrene foam, which is used for craft applications, can be identified by its roughness and the fact that it "crunches" when cut. Additionally, it is moderately soluble in many organic solvents, cyanoacrylate, and the propellants and solvents of spray paint. Another tradename for polystyrene foam is thermacol, originated by BASF for expanded polystyrene.

Should we outside of the US work on the surface angle and properties of a White Polystyrene cup?

I have disposed of all my disposable polystyrene cups.

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#10
In reply to #6

Re: Styrofoam Slide (May 2015)

05/02/2015 10:48 AM

I take exception to this Wiki article as it is somewhat misleading.

1. Both Styrofoam® and polystyrene foam are the same thing. The ONLY difference is the process used to make the end product.

2. The correct term is pre-expanded polystyrene beads. Coffee cups are made by putting a predetermined quantity of pre-expanded beads in a mold and injecting steam to expand the beads into a single mass.

3. Many inexpensive, clear "plastic" boxes are injection molded polystyrene.

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#11
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Re: Styrofoam Slide (May 2015)

05/02/2015 11:28 AM
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#8

Re: Styrofoam Slide (May 2015)

05/02/2015 7:08 AM

I suspect it's due to slip-stick; a little like bowing a musical instrument. Has to do with static and dynamic coefficients of friction.

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#9
In reply to #8

Re: Styrofoam Slide (May 2015)

05/02/2015 7:18 AM

More specifically, I believe slip-stick provides the non-linear exciting force, and the bowl vibration is caused by the object's response to to that non-linear exciting force.

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#27
In reply to #8

Re: Styrofoam Slide (May 2015)

05/04/2015 2:10 PM

But, but, if you put slip-stick on a pig, it is still a pig, and the slip-stick is still a slide rule.

A agree that this is similar to the build-up of stresses in a fault zone, where during a seismic event, the stresses overcome the "stick" part, and undergo rapid "slip", and continues to do so, until a sufficient stress releiving motion has taken place.

In the styrofoam cup, the reason the droplets travel so high is that the wavelet amplitudes undergo constructive interference at the cup's center of mass, and project this pressure upwards.

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#28
In reply to #27

Re: Styrofoam Slide (May 2015)

05/04/2015 4:17 PM

Thanks; although I was hoping for a GA, I guess I should appreciate that someone knew what I was talking about.

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#12

Re: Styrofoam Slide (May 2015)

05/02/2015 7:47 PM

Does the effect change using a short and wide cup versus a tall and narrow cup ? / Or a cup with a thick base or a thin base ? / Should the water be distilled or mineral water ?

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#13
In reply to #12

Re: Styrofoam Slide (May 2015)

05/02/2015 7:52 PM

Sounds like an excellent test for you to perform.

Let us know the results, with pictures.

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#14

Re: Styrofoam Slide (May 2015)

05/02/2015 7:59 PM

I still cant post pictures yet, send me your email and I will send you the pics and we can share the credit for the experiment.

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#15
In reply to #14

Re: Styrofoam Slide (May 2015)

05/02/2015 8:06 PM

Doesn't the green camera at the top of the reply window work for you?

Try it with any .jpg picture.

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#18
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Re: Styrofoam Slide (May 2015)

05/02/2015 11:22 PM

I take a picture, save it to the gallery, or to several other " file " ( whatchamacallits, like drop box, is that a program or a software ?) . When i try to load a picture to cr4, I get a message something like " nicht versten" or I cant understand your jpg. picture so too bad sucker, I ain't uploading it no matter how many times you cuss me out.

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#17
In reply to #14

Re: Styrofoam Slide (May 2015)

05/02/2015 8:48 PM

Your pictures may be too big. You can just wait longer or resize them with windows picture manager and 'save as' etc.

Jim

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#16

Re: Styrofoam Slide (May 2015)

05/02/2015 8:46 PM

When you first move the Styrofoam cup the water in side wants to remain where it is, the water then moves setting up a reactive force, this force resonates with the cups sides generating waves towards the centre that produces the droplets.

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#19
In reply to #16

Re: Styrofoam Slide (May 2015)

05/03/2015 4:26 PM

That explanation suggests that the same phenomena should occur even if the cup is made of something else, like paper or glass.

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#20
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Re: Styrofoam Slide (May 2015)

05/03/2015 5:28 PM

Yes it does? though I had not thought of it perhaps the hollow cavities in Styrofoam? have a effect on the production of the droplets?

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#21

Re: Styrofoam Slide (May 2015)

05/03/2015 7:51 PM

Vibration is at resonant frequency setting up standing waves in the liquid.

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#22
In reply to #21

Re: Styrofoam Slide (May 2015)

05/04/2015 8:52 AM

BINGO!! Now all we need is a non-linear forcing function, like the wetted plastic cup being wiped across the glass, to produce that resonant forcing function.

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#23

Re: Styrofoam Slide (May 2015)

05/04/2015 11:06 AM

The bottom of the cup does not set flat on table. It's is suspended above it. Styrofoam is flexible. Any vibrations will cause the bottom to flex up and down. Causing waves in the water up and down.

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#24

Re: Styrofoam Slide (May 2015)

05/04/2015 11:18 AM

This is really an exciting thread (groan)

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#25
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Re: Styrofoam Slide (May 2015)

05/04/2015 11:39 AM

Thanks for the help! ;-)

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#26

Re: Styrofoam Slide (May 2015)

05/04/2015 11:54 AM

I cant seem to get the table to move at that speed and the cup just stays in one spot

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#29

Re: Styrofoam Slide (May 2015)

05/04/2015 5:18 PM

Seriously, wouldn't the point on the cup at which you applied the force make difference?

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#30
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Re: Styrofoam Slide (May 2015)

05/04/2015 5:26 PM

If you apply the force on the side of the cup by whacking it with a baseball bat the contents really dance about

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#31
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Re: Styrofoam Slide (May 2015)

05/04/2015 5:43 PM

Wood or aluminium?

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#32
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Re: Styrofoam Slide (May 2015)

05/04/2015 5:51 PM

Maybe this will help.

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#33

Re: Styrofoam Slide (May 2015)

05/05/2015 10:15 PM

electrostatics, friction induced . Triboelectrification

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#34
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Re: Styrofoam Slide (May 2015)

05/05/2015 10:29 PM

Welcome.

It is not electrical.

Strictly mechanical.

Someone mentioned resonance.

Have you ever made a wine glass "sing" by rubbing a wet finger around its top rim?

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#35
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Re: Styrofoam Slide (May 2015)

05/06/2015 12:32 AM

If you like singing glasses, you are in good company. Ben Franklin like singing glasses enough to invent a musical instrument around the process, called the hydrocrystalophone, or the glass armonica.

.

https://youtu.be/eQemvyyJ--g

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#36

Re: Styrofoam Slide (May 2015)

05/06/2015 3:19 AM

What is creating resonance? There is the first action of motion. Second there is the calorific value of heat due to the coefficient of friction, and also the resonance of the Styrofoam cup. So, a velocity has been stipulated, on a smooth wooden surface, so does the friction of Styrofoam in motion generates some heat? which affects the coefficient of friction? which affects the resonance of the cup, which affect the resonant motion of the liquid to produce droplets? YES?

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#37

Re: Styrofoam Slide (May 2015)

05/08/2015 2:13 PM

the styrofoam cup swings (perhaps by resonance) by the resistance of the Wood surface

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#39
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Re: Styrofoam Slide (May 2015)

05/28/2015 1:18 PM

size of the styropor balls

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#40
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Re: Styrofoam Slide (May 2015)

05/28/2015 4:41 PM

Well sir, if someone were scooting yours across a wooden surface, you might make a vibration as well.

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#49
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Re: Styrofoam Slide (May 2015)

06/27/2015 2:17 PM

like chalk on teachers table!

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#38

Re: Styrofoam Slide (May 2015)

05/27/2015 12:05 AM

G'day. I know zip about this question but wondered if there might be a static charge build up in the cup and polarize the water? like charges repel and shoot the water out of the cup.

Not even 2c worth I know, but I did say I knew nothing.

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#41

Re: Styrofoam Slide (May 2015)

06/02/2015 9:56 AM
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#42
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Re: Styrofoam Slide (May 2015)

06/03/2015 4:15 PM

LOL!

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#43

Re: Styrofoam Slide (May 2015)

06/04/2015 1:30 PM

"The answer to this challenge will be posted later this month, right here on CR4".

Where?

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#44
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Re: Styrofoam Slide (May 2015)

06/05/2015 12:34 PM

That is the ultimate question - anyone who answers that challenge should be awarded Swami guru, or Ramakrishna Swami guru.

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#45
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Re: Styrofoam Slide (May 2015)

06/05/2015 1:03 PM

That and what happened to "Caption this"? Although it may be just me that is banned, due to stupidity.

Thanks, SlamiSlami Baloney.

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#46
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Re: Styrofoam Slide (May 2015)

06/05/2015 3:32 PM

I don't think you have been banned, and certainly not for stupidity.

I could be banned for thinking that my wife has become more nagative, for various reasons.

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#47

Re: Styrofoam Slide (May 2015)

06/26/2015 10:53 AM

Another challenge question without an answer. Maybe it should be required to provide the answer along with the question which would then be posted at the end of the month.

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#48

Re: Styrofoam Slide (May 2015)

06/26/2015 11:03 AM

I found the answer, I think...

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