How does one suck in a piece of spaghetti?
Alan "Uncle Al" Schwartz
edz...@aol.com wrote:
>Someone has raised the question: how does one suck in a piece of cooked
>spaghetti? It can't be as simple as, say, sucking milk through a straw,
>where sucking causes the air pressure over the milk to force the liquid
>up. If you push on the end of the spaghetti strand it just buckles.
>Perhaps one sucks in air AROUND the spaghetti, and the friction drags the
>strand along with it, but one has little sensation of taking in a lot of
>air when eating pasta. CCs by E-mail appreciated. For a newspaper column.
>-Ed
Alas, it is as simple as sucking milk through a straw. Air pressure
inside your mouth is lowered relative to that outside, your lips form a
suitably conformal orifice about the strand, the sauce is the lubricant,
and the differential air pressure drives it in.
Try sucking in a cooked strand without sauce (butter, olive oil, or other
grease). "Moving parts in contact require lubrication," Heinlein.
You can also entrain a strand within an airstream. As its contact with
your lips in this case is minimal, it will work on sticky spaghetti.
--
Alan "Uncle Al" Schwartz
Uncl...@ix.netcom.com ("zero" before @)
http://www.ultra.net.au/~wisby/uncleal.htm
(Toxic URL! Unsafe for children, Democrats, and most mammals)
"Quis custodiet ipsos custodes?" The Net!
edz...@aol.com
Joel Singerman
Alan "Uncle Al" Schwartz wrote:
> inside your mouth is lowered relative to that outside, your lips form a
> suitably conformal orifice about the strand, the sauce is the lubricant,
> and the differential air pressure drives it in.
>
> Try sucking in a cooked strand without sauce (butter, olive oil, or other
> grease). "Moving parts in contact require lubrication," Heinlein.
>
> You can also entrain a strand within an airstream. As its contact with
> your lips in this case is minimal, it will work on sticky spaghetti.
>
> --
> Alan "Uncle Al" Schwartz
> Uncl...@ix.netcom.com ("zero" before @)
> http://www.ultra.net.au/~wisby/uncleal.htm
> (Toxic URL! Unsafe for children, Democrats, and most mammals)
> "Quis custodiet ipsos custodes?" The Net!
Nice experiment to show that differential air pressure drives in the
lubricated spaghetti is to have a very very close personal friend suck on
the other end of the strand, and see how much harder you have to work to
get the strand into your mouth. The limits to this experiment involve
the tensile strength of cooked spaghetti and the limits of friendship.
Joel Singerman
fols...@aol.com
edz...@aol.com wrote:
>Someone has raised the question: how does one suck in a piece of cooked
>spaghetti? It can't be as simple as, say, sucking milk through a straw,
>where sucking causes the air pressure over the milk to force the liquid
>up. If you push on the end of the spaghetti strand it just buckles.
>Perhaps one sucks in air AROUND the spaghetti, and the friction drags the
>strand along with it, but one has little sensation of taking in a lot of
>air when eating pasta. CCs by E-mail appreciated. For a newspaper column.
There's a big difference between pushing on the end of a strand of
spaghetti and pushing equally on all of the surface that lies outside your
mouth. If you pressurized a limp strand of spaghetti to 100,000 psi all
over it wouldn't buckle, but both ends would experience a big force. If
one end were in a lower pressure area the strand would start moving in
that direction. The important thing to remember is that, under uniform
pressure, all sections of the spaghetti strand are subject to axial and
lateral compression and so reducing the pressure on one end creates a
*local* imbalance of forces where your lips seal around the strand.
Outside the seal, there is high pressure (including internal axial
compression) and inside the seal, there is low pressure and that results
in a net force sucking the stuff into your mouth.
You would be able to tell if you were sucking in air around the
spaghetti--it doesn't happen.
Mark Folsom, P.E.
Consulting Mechanical Engineer
lb...@aol.com
Im Artikel <57ia3s$a...@sjx-ixn8.ix.netcom.com>, Alan \"Uncle Al\" Schwartz
<uncl...@ix.netcom.com> schreibt:
>Alas, it is as simple as sucking milk through a straw. Air pressure
>inside your mouth is lowered relative to that outside, your lips form a
>suitably conformal orifice about the strand, the sauce is the lubricant,
>and the differential air pressure drives it in.
That of course is right for the knowing, but IMHO will not help the asker.
What is missing is the explanation where and why the difference in air
pressure "drives" the spaghetti, when it is neither rigid (so you could
push on the one end) nor a liquid in a straw. The obvious explanation
(which I suppose Uncle Al had in mind) is, that the cooked pasta 'feels'
the air pressure around it at every point of every slice you would look
at. You may imagine, that the surrounding air pressure tries to 'squeeze'
the spaghetti, but as the neighbouring slices to the right and the left
are 'squeezed' just the same anything stays in place. So if you only look
at the one slice that is exactly in the middle of the different fields of
air pressure (which is the orifice made by your lips), it gets more
sideways pressure from the outside, than from the inside, thus moves
inside. As it is tangled up with the next 'slice' it will drag the next
part of pasta into its old position and there happens the same again.
It is true, that there is some confusion, when you look at the usual
picture explaining the straw/fluid example. You usually see little arrows
of pressure pointing vertically down on the fluid in the glass 'pressing'
the liquid into the straw and up in your mouth etc. This of course is a
bit misleading. The fact is, that any pressure is equally distributed
throughout a liquid. Thus from the beginning of the straw to it's end any
particle 'feels' some more pressure from the glass side and a bit less
from the mouth side (under the assumption, that the rigidness of the
straw can stand the difference in pressure, otherwise it'll collapse), so
they all start moving. In the case of the spaghetti, this pressure
distribution works only locally as explained above.
Cheerio
The most dangerous untruths are truths slightly deformed.
Lichtenberg, Sudelbuecher
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Russell Blackadar
edz...@aol.com wrote:
> Someone has raised the question: how does one suck in a piece of cooked
> spaghetti? It can't be as simple as, say, sucking milk through a straw,
> where sucking causes the air pressure over the milk to force the liquid
> up. If you push on the end of the spaghetti strand it just buckles.
> Perhaps one sucks in air AROUND the spaghetti, and the friction drags the
> strand along with it, but one has little sensation of taking in a lot of
> air when eating pasta. CCs by E-mail appreciated. For a newspaper column.
It isn't friction, and you don't suck air.
Let's do a little thought experiment:
Consider what would happen if you chopped through the spaghetti
strand 1 mm outside your lips. The knife would create two new
circular surfaces in the spaghetti, and air would move into the
gap. Since the air would push equally on each new surface, and
in exactly opposite directions, the net force in the system
would be unchanged.
But clearly, the net force on the 1 mm stub in your mouth is
inward; this stub is so short we don't need to consider any
complications due to bending.
Just as clearly, the net force on the limp other piece is zero;
the air pushes on it from all directions with no imbalance, and
so it doesn't move (absent gravity, etc.).
In other words, we started with a system, altered it slightly
while introducing no new net force, and ended up with a system
of net inward force + zero force. By the law of conservation
of momentum, we must have started with a system of net inward
force. Q.E.D.
Of course, the original inward force was distributed over
entire strand, mostly on the outsides of whatever curves
were there, and transmitted down its length by the strand's
resistance to compression. That's why it's hard to visualize;
but nevertheless, it is there.
The strand does not buckle because there would be no reduction
of free energy in doing so -- the force would simply redistribute
itself to different curves. This differs markedly from the
situation where you push on the end with your finger.
--
Russell Blackadar, rus...@mdli.com
Doug Craigen
edz...@aol.com wrote:
>
> Someone has raised the question: how does one suck in a piece of cooked
> spaghetti? It can't be as simple as, say, sucking milk through a straw,
> where sucking causes the air pressure over the milk to force the liquid
> up. If you push on the end of the spaghetti strand it just buckles.
Think for a minute about what you've just wrote. What would happen if you
were to push on the milk. If you push on one spot, your finger goes inside,
nothing goes into the straw. This is much like trying to push the end of
limp spaghetti.
You recognised that it is the pressure over the whole surface of the milk
that is important. The same is true with spaghetti. There is pressure on
it from all sides. When you suck, the pressure is lower inside your mouth,
hence there is a net force on the spaghetti towards the inside of your
mouth.
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