Coffee Talk

I meant to add...

Some people think that the mass of the water is what changes the tone, and I think that it does so by altering the rate that the ceramic vibrates where the water is in contact with the glass.

This sounds similar to the mechanism behind quartz crystal microbalances (QCM). Crystal microbalance instruments or sensors use a piezoelectrically vibrated quartz crystal resonator to measure thickness and deposition rate in thin film or plating processes. As a film deposit builds up on the crystal sensor's surface, the vibration frequency changes providing an indication of the mass deposition rate.

Wikipedia Info on QCMs

The Wafer and Thin Film Instrumentation area on GlobalSpec provides a place to parametrically search for crystal microbalances and other thin film instruments.

Hello Hero! You were first and you're right.

The difference I hear is not slight - I would an octave. But you have to stir the coffee really fast.

Yes you're right. It's funny coincidence I just had enjoyed a coffee when noticed your post . I should be type answer at once but I can't as I adore coffee.

Have a nice day.

I suppose the coffee as any liquid is damper. So owing to excentric spinning forces level of coffee is some up and makes square of dry strip of cup (resonator) some less. It makes mass of resonator and therefore it's own frequency higher.

I have notice something similar only iI did not stir at all. It was only the mug heating up. Also note that that only 2 of my 3 mugs I have in the office does that.

The pitch went up by more than a octave.

you may tyhink this is nuts but consider the air volume that is chaged within the molecules of the cup as the liquid is rotated. faster moving in a circle liquid will produce a different sound level than liquid being stired in a strip like motion when it is held in a cup . french cooks have known about this for a few years the difference in making french style pastry is tasted in opposite to the stirring methods used in other countries. hitting the side of the liqid jar they stir the liquids in using thier system makes a different sound to the one made using the stirin methods of pastry chefs from other countries methods.

sparky i am sorry if the language is not too clear in this post what is left of my brain is working in a double stress mode for the past week

'da ber

I'm not going to be much help here, but this was set as an option for a physics project in my 1st year (BSc). I was tempted, but chose anharmonicity in vibrating steel strings. 'Fraid I don't know the outcome of the coffee-cup project - or even whether anyone took it as an option.

I've been wondering about the frequency-shift phenomenon (on & off!) since I was about 15.

If I started tapping on my coffee cup while stirring, the first noticable rise in pitch would be in my wife's voice !

Same thing happens when you tap with your spoon (inside) on the bottom of the (full) cup. And you don't have to stir ...

Same question : Why ?

C'mon boys ... keep tapping and refilling that cup ...

Beware of the sugar/caffeine high!

Basically, you are altering the resonance frequency of the cup by adding mass (liquid) to the cup. You can do the same thing if you glue appendages to the cup. However, anything you add needs to be pretty tensile or it acts as a dampening agent.

That begs the question of why water doesn't dampen the oscillations of the cup. Well, water is a pretty good acoustic transmission media. However, it still contains mass and when in contact with the cup wall changes the resonance of the cup wall's oscillation frequency by slowing it down. The more water in contact with the cup wall, the lower the resonance frequency and the lower the note it makes.

But the effect is observed after the cup has been filled! No extra is being added, and the stirring is such that the surface profile of the liquid is more-or-less constant - but the pitch still changes. I've found it difficult to reproduce - I tried last night with an initially cold cup filled quickly with water from a boiled kettle to within about 10mm of the top, then rapidly stirred. I didn't notice any change - tho' I'll swear there's been a change while stirring the makings of instant coffee (incl. sugar) in otherwise similar circumstances in the past.

This clearly needs a lot more research!

I was able to reproduce it with cold water. Part of the issue may be the cup itself. I would not use a styrofoam cup. ;-)

Essentially, when the liquid is stirred, the liquid will cover a greater amount of the cup's surface and increase the area coupled between liquid and cup; thus changing the frequency of resonance for the cup.

The better the cup's quality, the better it will ring. Crystal glass does extremely well. Ceramic usually works very well, too, but if the grade is poor or it has a crack, it will not resonate well at all.

I would bet that you could get the same effect if you struck a tuning fork and partially submerged it in water. Somewhere I have one and if I think of it tonight I may give it a try.

"This clearly needs a lot more research!"

Lets set up a Six Sigma DMADV methodology immediately.

THAT is an excellent idea! ;-)

this is discussed in "How to fossilize your hamster" which I don't have to hand.

Hamster with or without the bell?

Empty vessel thunders much louder.

Ceramic is a poor conductor of heat. The tension will change as the heat spreads through the wand.

I wonder if the pith of a porcelain dinner bell will change with temperature?

Maybe the menu can be determined by the sound.

I have a stainless steel mug at home and will sound test it tonight.

Hi bhankiii,

I'm a heavy coffee drinker, so I'll try this: it has to do with the Doppler effect. The spinning liquid is elongating the sound wavelength directly proportional to its speed. After the initial tap, each point on the cup sends a wave to the center but the reflected wave has a lower frequency because the liquid is in a different reference system that moves away. Another thing is that the mentioned point on the cup never gets back the wave generated by it but a different wave generated by another point upstream. Under certain conditions (phase and amplitude), the combination of the ceramic oscillation and water oscillation (if they are close) could result in a beat frequency transmitted to the air from where our ear is picking it up.

Congratulations for your sense of observation.

Regards,

Michael

That's an interesting idea.

That would imply that there are two effects that cause frequency shift.

1. The static level of liquid in the cup (remember: pitch changes relative to the amount of fluid in the cup).

2. The dynamic motion of the fluid.

If number two has merit, can we think of another scenario where this happens? The first thing that comes to mind is free air. If I listen to a guitar string that is plucked in my living room, will it have the same pitch outside on a windy day as it does inside?

In the case of the guitar string; yes, they sound the same.

However, I recall many times when I was a kid how my mother's voice would sound much higher when she was calling for me when I was outside rather than when I was inside the house. ;-)

"That would imply that there are two effects that cause frequency shift.

1. The static level of liquid in the cup (remember: pitch changes relative to the amount of fluid in the cup).

2. The dynamic motion of the fluid.

If number two has merit, can we think of another scenario where this happens? The first thing that comes to mind is free air. If I listen to a guitar string that is plucked in my living room, will it have the same pitch outside on a windy day as it does inside?"

Well one way to see if number 2 has any effect is if you have two similar cups with similar coffee, and similar so on, and your variable is the amount of coffee in the cup, with one cup still, the other cup being stirred so it covers the same amount of surface area as the still cup, and if the two have different sounds, then yes there would be the "doppler" coffee effect.

I can just do that with the same cup by adding water after I stirred it.

However, how does that prove that the effect is due to doppler?

Hi Anonymus,

The natural frequency of resonance is given by the inertial mass of the system. In this case, the slightly increased level of liquid due to rotation cannot change that frequency as the mass is unchanged. Only the mass distribution is different (parabolic concavity).

The coffee experiment generates a cyclic recombination of waves during the ping-pong between the wall of the cup and its center where all are reflected. I find this experiment quite fascinating and a mathematical model of it could be a little bit complicated. There are three mediums of sound propagation, boundary layer conditions, speed and temperature gradients, phase shifts, etc. The output sound frequency and amplitude are the product of several processes. But overall, I still think that Doppler effect is the dominant phenomenon involved.

Your wind example has nothing cyclic but could lead to an indirect measurement of wind speed similar to a Doppler flow-meter.

Hi Hottech,

the mass will change considerably - not the total mass - as the effective mass is given by the incremental small mass element times its effective (radial?) amplitude².

This is a continuous system where on any mass element there is an equilibrium of forces: inertial, elastic and viscous (to be neglected).

So the surface will move in a i,k pattern with i half waves in diameter and k half wavelengths in circumference.

(Similar to the TEM i,k modes of a laser beam or the similar modes of a vibrating disk.)

So the mass that is added by rotating the fluid is given by the shape (paraboloidal) that takes the surface upon rotation and the square of the amplitude (think about radial in direction).

In the simplest mode the velocity is highest at the rim and zero in the center.

And the amplitude is higher at the boundary of coffee and air than below near the center.

So estimate the velocity distribution and integrate ....

But don't forget the coffee.

Doppler effect can be effective only at very high modes that will be damped to non- existence.

You can think it also as the elastic energy of the coffee-pots deformation coupled to the kinetic energy of the moving masses (cup plus coffee plus a little air) will give the natural frequency.

RHABE

P.S. we shall start an effort to build a new and better coffee-machine:

First part: roasting green coffee beans with hot air,

second part: grinding

third part: brewing

fourth part: pipeline to me.

Stirring my coffee will never be the same again.

Hi Rhabe,

I like the idea with the coffee pipeline. However, making coffee is one of my favorite rituals.

Let's see first what is making the audible sound here. The "loudspeaker membrane " is the lateral outside wall of the cup. Up to a point, I would compare this experiment with this one:

take a loudspeaker and measure it's resonance frequency when having it's axis in a horizontal position. Then put some gel or other sticky substance on the membrane, in a concentric symmetrical pattern and measure it again. The new frequency will be lower than the first one as more mass was added to the resonator. Another thing is that the new frequency is not influenced by the distance of the gel from the rim, similar to the hight of the liquid in the cup (better said by the distribution of gel mass) as long as it preserves a cylindrical symmetry, but only by the quantity.

The coffee itself is not making any sound but is a better sound transmission medium than air. When the coffee is at a standstill, the cup is oscillating like a heart (just a visual representation). Inside it, all combinations of direct and reflected sound are made in a perfectly symmetrical pattern visualized by the small circular waves on the coffee surface. The coffee is acting like the gel on the loudspeaker's membrane, lowering the resonance frequency of an empty cup.

When the coffee is stirred, the equilibrium of the symmetrical pattern of sound combinations inside the cup is ruptured in a cyclonic pattern. Additional radial and tangential forces are acting on the oscillating water molecules. Among them, the radial ones are more important as they "press" the inside wall of the cup from inside to outside. The effect on the "loudspeaker membrane" is similar to adding more mass to the resonator.

Overall, the centrifugal forces combined with the Doppler effect inside the coffee make the resonator to lower it's frequency of oscillation. From my point of view, this might be the most complete answer. Everything depends on the dynamic influence of water on the contact with the inside cup wall.

I think we both had a convergent view of the process.

Regards

Hi Hottech,

the loudspeaker may or may not be a good example.

Most loudspeakers I did put to pieces had a rigid (lightweight) cone supported in a flexure at the rim.

This will act like a piston so any mass added is moving with the same amplitude regardless the position.

This is not like the coffee cup.

If you take a membrane that is elastic in itself and attach it rigidly at the rim then the resonance frequency will change with the position of the added mass.

RHABE

Actually, adding mass to the cone of a loudspeaker will lower its resonance frequency.

The piston excision of the cone will change with added mass and no loudspeaker is flat across the frequency range, so amplitude does change.

However, adding mass also adds some distortion to the waveform as the inertia of the mass prevents the cone from moving perfectly true to the electrical waveform.

Can you think of other factors that will change the resonance frequency of a loudspeaker?

Hi AH

"adding mass to the cone of a loudspeaker will lower its resonance frequency"

Naturally, nobody doubts.

"no loudspeaker is flat across the frequency range, so amplitude does change"

I did not think about amplitude as function of frequency but of amplitude as function of radius and circumferential angle.

So if you think of the first resonance when the rim (outermost) has the biggest amplitude of the vibration then any mass added where the amplitude is maximum then the influence on resonance is biggest.

If there is a "vibration knot" - a zero amplitude of displacement - then adding mass there has little if any influence.

But if on stirring the coffee the mass of water is partially displaced towards the outer rim those resonances with maximum amplitude of displacement at the rim will go down in frequency but those resonances with nearly no amplitude at the rim will go up in frequency as the coffee added there is missing at the regions of maximum amplitude.

"However, adding mass also adds some distortion to the waveform as the inertia of the mass prevents the cone from moving perfectly true to the electrical waveform."

I don't believe in this except you think about the same amplitude of motion which would require much more force if mass is added thus more current and this higher current will generate distortions as to the permanent magnetic flux is superimposed the additional magnetic flux generated by the current in total nearer to saturation and thus having more harmonic distortions.

"change the resonance frequency of a loudspeaker"

I did not really measure these but I would estimate that the temperature dependency of the elastic properties of the material used to mount the cone: the "spring" in this system will give a considerable influence. Similar will act the temperature coefficient of the magnetic flux that is generated by the permanent magnet.

There will be also some minor changes from the expansion of the coil with temperature and the expansion of the magnet assembly with temperature resulting in radially stressing the mounting screws or glue of the magnet.

RHABE

Why don't we just be done with it and use a conical loudspeaker for our coffee cup. Of course we'll have to hold it by the magnet however.

Better yet lets just use a really big loudspeaker such that we can put on our "speedos" and get in so we can "feel" the frequency changes. In other words, lets get right on down and feel the music.

O.K. Roy! I.m ready! Plug it in and turn on the power....

While we're in there we can tap the rim of the speaker (with our paddle) to the tune of "tap, tap, tap that speaker rim". <sung to the tune of "smoke, smoke, smoke that cirgarette">.

Come on guys, don't you think a coffee cup (with all the implied wisdom in the bottom of a teacup) has gotten just a little bit silly?

Hey, JJ, let's get that frequency sorted out - we can heat the coffee while we're listening (2 x ultrasonic channels, one fixed, the other modulated so the sum/difference gives us the music - combined power sufficient to heat the brew.)

KrisDel™ - We'll cut you in.

I think we can rule out the doppler effect. I was just kidding about that.

The speed of sound in a warm liquid is about 1500 m/s.

If you stir a liquid in a cup with an inside diameter of 7.5 cm at a rate of 1 revolution per second you get a speed of the fluid along the inside edge of the cup of about .24 m/s.

A change of .24 m/s is something like 0.016%, which is nowhere near enough to account for the change in pitch we hear, don't you agree?

"The spinning liquid is elongating the sound wavelength directly proportional to its speed."

Seems to me that if a doppler shift is involved the net effect would be cancellation and no change in frequency. For example:

Suppose I'm stirring the coffee in a clockwise direction (looking down at it). Now I tap the cup at, say, point A on the rim. Wavelength would be increasing to the left of point A, but would be decreasing to the right of point A, hence cancellation.

And if true, stirring it anti-clockwise should change the pitch in the other direction?

True story Anonymous,

When I was maybe 3 or 4 yrs old I would watch my dad put sugar in his coffee then stir it to sweeten it. I asked him if he stirred it in the other direction would the coffee get unsweetened. Don't remember what he told me for an answer.

If we stir it in a random fashion; figure 8, oval, clockwise then anti-clockwise, etc., maybe we could modulate the tone produced by the tap and have a new kind of musical instrument. (don't let KrisDel™ hear about this)

Hi JohnJohn,

Waves cancellation is quite a rare exception. They have to be 180° out of phase, to have identical amplitudes and frequencies. Their direction of propagation/collision is also important and defines the limited region of space in which cancellation could occur. Ask someone experienced in active noise cancellation who can tell you how complicated is and what deceiving results are often obtained.

All these are very unlikely to happen in this experiment, mainly by the fact that sound propagation in water is dragged on curved trajectories converging to the center of rotation. In fact, what I find most complicated to describe is the propagation of sound in the spinning water and the recombination of reflected waves.

A rigorous measurement of sound could reveal that is not a pure tone but a complex sound that can be dismantled in a Fourier transform. Again, it's about a multitude of simultaneous processes, but only one of them is dominant: Doppler effect. As I explained earlier, this experiment resembles to a Doppler flow-meter. The flow through a radial section of the cup is a function of rotational speed and is measured with sound! Q.E.D.

I think we all drink to much coffee

how to fossilize your hamster page 46; anonymous hero came close when he mentioned air before anyone else. "when you pour hot water on instant coffee many of the volatile components form tiny bubbles.. also water has dissolved air and when added to powcers such as coffee nucleation sites form around the sites and more bubbles are generated. The air bubbles lower the speed of sound in the liquid by making it more compressible..it takes longer for the sound wave to travel between the botton and the surface.. then as the bubbles rise to the surface and burst the sound travels faster and the pitch rises... greatest different in pitch is noted when the spoon is tapping the bottom of the mug."

I don't drink instant coffee. And I'm very offended by your suggestion.

I agree. Instant "coffee" is not coffee! (from a coffee connoisseur)

I don't either, which is why I have not noticed this. It's either Lavazza Rossa from my espresso machine (which I even take on a cycling tour) or Douwe Egberts (£1 for 250g from Nettos) in a filter at work. I was just passing on the info. - don't shoot the messenger.

How do you repair a porcelain dinner bell that broke while hitting it with a spoon to test the frequency change due to hot water?

(My wife inherited the thing from her Granny - she will kill me dead )

Rut-ro.

Hi Hendrik,

Now you understand why Einstein was doing only thought experiments!

All I can do to help you in this desperate situation is to suggest:

Plan A: bring bhankiii to court and take him the money for damage, including your hospitalization after you're telling your wife the news... Now you understand why all of us here are hiding behind false names!

Plan B: try to explain to her that Science is asking (sometimes) for sacrifices. Bag her to spare you as you didn't mean the supreme sacrifice...

Plan C: call CNN and tell them you've been abducted by aliens exactly when you were drinking your coffee and they broke the cup while doing a strange experiment. All you could understand from their language was: bhankiii, bhankiii...

I happen to have a set of 10 Norman Rockwell porcelain bells that I picked up in a garage sale for $10. They are at your disposal.

Two drops of super glue and the problem is solved.

hottech I did not even have to use one of your plans.

bankii thanks for the offer, maybe I can experiment again.

My wife came to me with the bell and the handle in her hands and asked if I had some glue. She accidentally dropped it the other day and the glue she used did not last.

I think it dissolved in the hot water.

Again thanks for the brotherly support in my darkest day.

Nobody has cited the Coriolis effect yet.The mention of Coriolis when discussing spinning thingies usually truncates the argument as no one will admit they're not sure what it is.

I've a coriolis based flowmeter about 1M diameter so I'm going to bang it with a hammer while varying the motor speed. Results later if I'm not carted off to the funny farm.

I have noticed the Coriolis effect - but that usually comes a while after I've had my coffee.

oldeng,

I have wondered about the coriolis effect. Especially since moving to my present property. My kitchen sink has two basins. Upon emtying them simultaniously, one flows clockwise and the other counter-clockwise. It is my understanding that north of the equator it should be clockwise and south counter-clockwise (or is it the reverse of that, I can't experiment right now).

According to received wisdom the equator runs between your two sinks.Bet you didn't realise that! However,to exclude other factors,please uninstall the sinks,and reinstall after rotating 180deg,i.e.you and the sink,or just the sink,all in the interests of science so you can't refuse.Use your GPS to ensure that they are installed exactly at the same latitude.We await your report.

Apologies to those waiting patiently for the results of the 1M coriolis 'coffee cup' hammer bonging,the weather in sunny Scotland has precluded attempts,the howl of the wind obscured the ring of the bong.Forecasts are for gales with rain, moderating to severe storm.Perhaps somebody with an indoor plant could have a go?

Afraid I can't do that right now. I did, however, move the trailer that contained the sink (as well as the rest of the accessories contained therein) to another spot. The sinks now both drain properly counterclockwise. Sorry to hear about your inclement weather. Perhaps you too should move to another spot. Seriously though, the area I live in has quite a mixture of mineral deposits due to a combination of volcanic action (long, long ago) and glacial deposits (also long ago, duh) so I am wondering about the possibility of a large chunk of magnetite near the surface. The trees (lodgepole pine) growing right around the former site are all stunted, crooked and die off early. This is an area of about 1/2 acre.

Any UFO activity in your area?

Absolutely rife with it. Bigfoot, however, is not seen as often.

Hahahahaha... ROFLOL!!!

Good one.

I think that's just an old engineer wives tale. I would be curious to know, though, do they empty in the same direction when they drain separately?