The Spaghetti Incident?

[Irishman]

from Jinx:

Then, I assumed my pucker has a diameter of 1/4".

I believe this is an unfounded assumption. What makes you think your mouth is open and not closed tight around the noodle?

While recently sucking on a straw to enjoy a thick shake, I discovered I could breathe normally through my nose yet still create a partial vacuum in my mouth itself…“pulling up” the shake into the mouth (without swallowing). This shouldn’t be, and it indicates there may be some valving in the anatomy permitting this.

I think that valving would be your tongue. If you push the back of your tongue up against the roof of your mouth, you create the vacuum seal, allowing your mouth to hold the contents of the straw, while breathing through your nose. Experiment with this a little - but be careful, as you might choke if done improperly. The risk is your’s to take, so no lawsuits.

I don’t discount pneumatic conveying, but I don’t think it plays any role in sucking a noodle. I think you can generate the same effect with a boiled egg - it’s a similar consistency in a much greater diameter.

I guess I’ll have to break down and slurp some spaghetti some time soon. (I quit that when I left elementary school.)

[Jinx]

Irishman, while I agree the 1/4" pucker “annulus” model is liberal, I am not so sure the seal between lips and spaghetti is an air-tight seal. And, regarding the milkshake and suction, I didn’t happen to notice the tongue’s position…you may be correct.

I’m not so sure this subject will ever be laid to rest!

[The_Ryan]

Originally posted by Jinx:
Well, in closing, all I can say is that while a small differential in air pressure may motivate the air, we are often observing the supplemental effects of velocity - not just dP.

Well, I think that dP is the ultimate cause, since it’s dP that would be causing the velocity.
And don’t you think that 700 ft/hour is an incredibly low velocity? That’s about .059 m/s, or 5.9cm/sec.

[Irishman]

In order to prove my point, I was forced to eat pasta and suck it.

I had pasta for lunch today - it was fettucine (rectangular cross section), not spaghetti, but it serves the purpose.

First, I could suck the noodles dry or with sauce. There was more friction when dry, and the sauce aided as a lubricant, but I was successful with dry noodles.

Second, I sucked successfully when lips closed around the noodle. I tried with my lips parted, allowing an air gap, and was unsuccessful. In fact, it was hard to keep the noodle from falling out of my mouth without holding it with my lips.

Third, if you squeeze your lips tightly on the noodle, you can affect the sucking by squeezing too tight and increasing friction.

Fourth, I observed it is not easy to judge how your lips shape. I think they more easily conform to the shape of the noodle than some people realize. Even though your pucker is an annulus shape (donut), the lips have some give in the flesh around the muscles. That tissue conforms around the noodle without conscious control.

I invite you to try these experiments yourself, like I did - in a public place. (I don’t think anyone noticed, or at least they didn’t say anything.)

As for the entrained air concept, perhaps someone could follow up with an experiment testing how much air flow it takes to float a noodle. I’m thinking something in a wind tunnel, variable speed air. But I think I’ve done my bit.

The answer is "Your lips seal around the noodle, the air pressure pushes the noodle at the cross section that blocks the opening, and the noodle slides into the mouth.

[Jinx]

To “The Ryan” and “Irishman”: Combining your remarks, the wind speed is NOT supposed to be high enough to “float the noodle such as in a wind tunnel”. The image you have is full entrainment, but partial entrainment is also possible at low velocities between 500-1000 ft/hr. But, I will go back and double check my sources to verify…just for you!

In regard to dP, Ryan, I was trying to say that dP is the indirect and underlying cause. But, it is not strictly THE cause IMHO.

(This topic really sucks!)

[Jinx]

I know it’s been a good while since we’ve kicked this question around. However, I had an additional thoughts about the partial vacuum we can create in our mouths. The answer to the puzzle is “aspiration”!!! This is the same effect that pulls fumes from a chimney. The effect of “aspiration” is created when air moves across an opening. (In technical terms, the air’s velocity vector is perpendicular to the opening’s area vector - which is always normal to the surface, by definition.)

The truth is our nose, mouth, pharynx, and lungs are arranged in such a fashion that can create the aspiration of foods into the mouth. With the mouth closed around a piece of spaghetti, we create “sucking” by drawing air in through our nose into the lungs. At the point when the air passing through the pharynx, the “chimney effect” (aspiration) occurs. The stream of moving air in the pharynx is perpendicular to the air particles within the mouth. (The moving stream of air passing from the nose to lungs forms a tee with the mouth cavity.)

Hence, the stagnant air in the mouth becomes entrained with the moving air stream. The moist spaghetti noodle becomes easily entrained as well. If you think about it, when we drink a soda or a thick milkshake, the same thing occurs. With soda being of low viscosity, it seems like a no-brainer. But, what about the thick milkshake? I’d wager the moist spaghetti noodle is quite easily entrained…esp. in comparison to a thick milkshake! When drinking soda from a straw, I’ve never observed any appreciable trouble eating (sucking) spaghetti noodles! But, give me a strawful of a thick milkshake, and I’ll always feel a need for stronger lungs! Perhaps many can relate to this…

Anyhow, in brief, it is the effect of aspiration inducing entrainment (as I described in greater detail previously within this thread) allowing the spaghetti and thick shake, alike, to be “sucked”.

Of course, this will spark more debate rather than settling the issue! - Jinx

[Jinx]

*Originally posted by Jinx *
…When drinking soda from a straw, I’ve never observed any appreciable trouble eating (sucking) spaghetti noodles! But, give me a strawful of a thick milkshake…

This SHOULD have read:
…Like drinking soda from a straw, I’ve never observed any appreciable trouble eating (sucking) spaghetti noodles! But, give me a strawful of a thick milkshake…

• Jinx

[Irishman]

I don’t think aspiration is involved. Try sucking in while pinching your nose closed.

In the efforts of science, I just tried sucking a raw piece of spaghetti. Almost no movement whatsoever. However, I’m pretty sure this is the result of friction. In order to close my pucker tight enough to seal around the “stick”, I’m creating too much pressure with my lips and thus creating too much friction for it to slide.

I’m not convinced entrained air or fluid drag from the sauce plays any roll. If you have any part in your pucker to allow space around the noodle, the noodle does not move in and the air flows past it. Seal around the noodle, the noodle moves.

Before there were comments about not being able to push a rope, etc. Funny, I can thread a needle. Thread is essentially a rope. However, it has some rigidity for the length involved. Similarly, I can push a rope of reasonable diameter, within a small length from the point of holding. The trick is to be within the structural integrity of the rope. This has to do with fiber type, weave, and probably some other factors, but within a certain range you can push a rope. I submit it is something on the order of a few diameters, depending on the aforementioned factors. Same thing with the limp noodle. While pushing from the end will cause bending just like a rope, pushing within a couple diameters of the opening of the mouth will likely be in the structural integrity range to push the noodle as a stiff object. The rest of the noodle dangling to the plate gets pulled along, till it is the part near the opening.

I think there’s a difference between the thick milkshake and a noodle. The milkshake is a highly viscous fluid trying to move through the straw, giving a long region of friction. The noodle is a solid moving through a short region of friction (the pucker).

[zut]

Spaghetti-sucking has nothing to do with air entrainment. If it did, you should be able to part your lips slightly and suck hard (drawing in air at high velocity), and pull in the spaghetti more effectively than you can close-mouthedly. In addition, there’s already a perfectly good explanation for how the spaghetti gets into your mouth: the pressure difference. Let me quote, with a little updating, from my own post in another spaghetti thread:

Quoted with some alterations.
First, let’s look at Cecil’s answer (which moght look a lot like “entrainment”). Cecil’s answer was that “Those particles striking the spaghetti close to the point where it entered the mouth, and whose vector had some inward-pushing component, would force it in.” However, this explanation is, well, silly. Any place on the surface where air particles strike has air particles striking in all directions. The force from any particle having an inward-pointing velocity is (statistically) canceled by a nearby particle having an outward-pointing velocity. So: forget this answer for the time being.

Next, let’s look at entrainment. Hopefully it’s obvious that any air drawn into the mouth is drawn in because of the pressure difference from outside to inside the mouth. The shear force transmitted from air to spaghetti is a function of the air velocity and of the viscosity of the air…which is pretty low. Low enough that very little force can be transferred from air to spaghetti. So forget entrainment for the time being.

Third, I think the confusion here arises because people tend to misapply their intuition (which is usually reliable) to this problem. Any thought of “forces” and “pushing” leads to the inevitable “you can’t push on a rope” argument. People forget that air pressure is not equivalent to a single force; it is a pressure exerted everywhere. So: forget your intuition for the time being.

Finally, where does the air pressure force act? Or, more properly, how does the force act? Thought experiment: an astronaut floats a piece of spaghetti in front of him in the Space Shuttle (no gravity = easier thought experiment). Does the spaghetti move? No; the air pressure forces are balanced (No Force, no massXacceleration). Now imagine a tiny cubic chunk of the surface of the spaghetti. There is air pressure on one side of the cube; the other sides are buried in the spaghetti. Does the cube move? No; the air pressure force is balanced by compressive forces within the spaghetti material.

Under air pressure (a hydrostatic load), these compressive forces (stresses, really) are equal in all directions within the spaghetti. You can slice the strand in any place at any angle, and the internal stresses are all equal to the air pressure. You can prove this by another thought experiment: The aforementioned astronaut cuts the spaghetti in some random place at some random angle. Do the two halves suddenly fly apart? No; the forces still balance; the air pressure now between the two halves is equal to the internal stress that was there before the cut. No change.

Now, for the sucking of the spaghetti. Another thought experiment: The astronaut gently places the strand in his mouth and lightly closes it. Air pressure everywhere is constant; internal stresses are constant. Cut the spaghetti just outside the astronaut’s mouth. There’s no change except air pressure has now replaced internal stresses in one plane. But, here’s the key: There is no place in the spaghetti strand that is affected by the cut. All the forces are still the same.

It should now be intuitively obvious that when the astronaut starts sucking, the very very short strand of spaghetti will be pushed into his mouth by the difference in air pressure. And this case having a short strand is equivalent to the case of a long strand.

Or, if you prefer, it’s the difference in compressive stresses outside and inside the lips that causes the strand to suck in: the stresses are caused by the air pressure.

Does that make sense? The explanation is perhaps a little more convoluted than Cecil’s, but it is (ahem) correct.

And, I should point out, there is entrainment (of sauce, if nothing else). But it’s an effect of the spaghetti being sucked in, not a cause.

[zut]

Even though it’s three years old, I probably ought to comment on this, too:

Originally posted by The Ryan (in two consecutive posts)
I believe I have already explained why [a spaghetti strand] won’t, under certain circumstances, buckle. If two opposing forces have the space between them completely filled with noodle, they will be transmitted through the noodle, cancel, and cause no net force and no buckling. Would you care explaining why you think it would buckle, or do you expect us to just take it on faith?

[…]

And another thing to consider: if all forces, even when canceled, cause buckling, why is it that a noodle laying on a plate, with forces cancelling all over the place, doesn’t buckle? Why doesn’t it just fold up under all the pressure?

Buckling is not caused by uncanceled forces (in fact, if the forces are uncanceled, there’s an acceleration). Buckling is caused by instability. If you consider the simplest case of a slender vertical column (made of spaghetti, or wood, or concrete, or what-have-you), and ignore all the air pressure and gravity forces, and then apply a load on the end of the column, you wind up with a two force member: a force on the top, and an equal and opposite force opposing it at the base.

If the column load is above some critical value (usually denoted P[sub]cr[/sub]), then any infinitesimal horizontal deflection of the column causes an off-center moment, which will increase the bending of the column, overcoming the resistance of the column. This is an unstable system, and the column buckles. If the column load is below P[sub]cr[/sub], then the stiffness of the column will tend to correct any infinitesimal horizontal deflection. In a real column, things are more complicated of course, but the bottom line is that columns buckle even if the forces are perfectly aligned.

Now, experiment time: hold a piece of spaghetti vertically between your forefinger and the table. Press lightly, and the spaghetti buckles, correct? Now pinch the middle of the spaghetti with your other hand, effectively bracing it in place. Try again to buckle the strand. It ought to be harder to do (four times harder, as a matter of fact). In the same way, if air pressure affected only the ends of the spaghetti, then it would buckle on the plate. But the air pressure also supports the circumference of the spaghetti, just like your hand does. And that’s why the noodle won’t buckle on your plate.