If temperature is motion, why doesn't stirring water make it boil?

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Discussion Overview

The discussion revolves around the relationship between temperature and molecular motion in fluids, specifically questioning why stirring or shaking water does not lead to boiling or a significant temperature increase. Participants explore various aspects of this concept, including historical references and practical applications in engineering.

Discussion Character

  • Exploratory
  • Technical explanation
  • Debate/contested
  • Historical
  • Mathematical reasoning

Main Points Raised

  • One participant questions why stirring a fluid does not cause it to boil, suggesting that molecular motion should increase temperature.
  • Another participant challenges this assumption, implying that stirring could indeed raise the temperature due to internal friction, although they doubt it can be achieved by human effort alone.
  • A historical reference is made to James Joule, who measured temperature increases through mechanical work, implying that stirring could have similar effects.
  • Participants discuss engineering projects involving heating water through mechanical means, sharing anecdotes about prototypes and efficiency considerations.
  • Some participants mention the potential for machines to generate significant heat through vigorous stirring, citing examples from industrial processes.
  • There are humorous remarks about unconventional methods of heating water, including a reference to a hot tub heated by a treadmill setup.
  • Technical discussions arise regarding the efficiency of mechanical systems, such as bevel gears versus cables for transferring energy in windmill designs.
  • Concerns are raised about the effects of torque and resistance in mechanical systems, questioning how to maintain proper orientation in wind-driven devices.

Areas of Agreement / Disagreement

Participants express a mix of agreement and disagreement regarding the effects of stirring on water temperature. While some suggest that stirring can raise the temperature, others remain skeptical about the practicality of achieving boiling through this method. The discussion includes competing views on the efficiency of different mechanical systems and their implications for heating fluids.

Contextual Notes

Participants reference historical experiments and practical engineering projects, but there are unresolved questions about the efficiency of energy transfer and the specific conditions required for significant temperature changes through stirring.

Who May Find This Useful

This discussion may be of interest to those studying thermodynamics, fluid dynamics, mechanical engineering, and anyone curious about the practical applications of temperature and motion in fluids.

Bradley in SD
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If the temperature of a fluid is a result of the molecules bumping into one another, why doesn't stirring or shaking a glass of water make it boil? Or at least raise its temperature?

Thanks for any help with this!
 
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How do you know it doesn't? That's a Joule of a question!
 
If you (:-p TVP; I'm ignoring you) shake or stir a container of liquid vigorously enough, it will boil as a result of internal friction raising the temperature. I don't believe that it's humanly possible to do so, but a machine might be able to pull it off.
 
when i was an undergrad at the U of North Dakota (the 1970s), one of my high school classmates chose engineering at our arch-rival, North Dakota State. anyway i visited him once at his school (NDSU) where he showed me a project he was working on (he was ME, even though i am EE) about heating with wind power. here is how two different engineering (students) think: i thought "windmill shaft connected to generator with electric cables connected to resistance heating in the living space." these MEs were thinking: "windmill shaft connected to tough-a ss lubricated mechanical cable that goes into living space where it churns up some big vat of water." they had a 1/10th-size prototype where they could drive the shaft with an electric motor for demonstration/testing purposes. i was surprized how quickly the water in that 10 gallon tank heated up.
 
Who'd a thunk...? Interesting.
I wonder how much extra heat was lost to internal friction of the cable. A bare driveshaft probably would have been even more efficient.
 
The guy that invented most of thermodynamics had a job drilling the big hole down the middle of brass cannons - which was done in a bath of water to keep them cool.
 
rbj said:
when i was an undergrad at the U of North Dakota (the 1970s), one of my high school classmates chose engineering at our arch-rival, North Dakota State. anyway i visited him once at his school (NDSU) where he showed me a project he was working on (he was ME, even though i am EE) about heating with wind power. here is how two different engineering (students) think: i thought "windmill shaft connected to generator with electric cables connected to resistance heating in the living space." these MEs were thinking: "windmill shaft connected to tough-a ss lubricated mechanical cable that goes into living space where it churns up some big vat of water." they had a 1/10th-size prototype where they could drive the shaft with an electric motor for demonstration/testing purposes. i was surprized how quickly the water in that 10 gallon tank heated up.

That's how they heat the hot tub at Slippery Art's Saloon in Dodge. They put the barman, Lars, on a treadmill and put a picture of the Lennon sisters on the other end.

Takes a while, but what the heck else can you do when it's -28 outside?
 
Danger said:
Who'd a thunk...? Interesting.
I wonder how much extra heat was lost to internal friction of the cable. A bare driveshaft probably would have been even more efficient.

in fact, that was another design they were working on with a shaft. but how do you connect the driveshaft going up the middle of the windmill tower, to these blades? with a 90o bend, that can't be too awful efficient. also, how do you keep the windmill pointing toward the wind when there is constantly this torque on the windmill platform that wants to turn it? i don't know the answers, it's what came to my mind then as it intrigues me now.

BTW, Bradley, ND beets SD anyday! :smile:
 
Bradley in SD said:
If the temperature of a fluid is a result of the molecules bumping into one another, why doesn't stirring or shaking a glass of water make it boil? Or at least raise its temperature?

Thanks for any help with this!

This is exactly what Joule did some 150 years ago. He did not make it boil but he DID measure a rise in the temperature (and the reason he could do that was that he was a brewer, meaning he had access to good thermometers).

wiki
http://en.wikipedia.org/wiki/James_Joule
 
  • #10
rbj said:
in how do you connect the driveshaft going up the middle of the windmill tower, to these blades?
... also, how do you keep the windmill pointing toward the wind when there is constantly this torque on the windmill platform that wants to turn it:

Bevel gears are probably more efficient than a cable. Hypoids would keep it fairly quiet, as well. Orientation is simply a matter of putting a 'tail' on the nacelle.
What the hell do beets have to do with this? They're one of the most disgusting vegetables on the face of the planet.
 
  • #11
Danger said:
If you (:-p TVP; I'm ignoring you) shake or stir a container of liquid vigorously enough, it will boil as a result of internal friction raising the temperature. I don't believe that it's humanly possible to do so, but a machine might be able to pull it off.
Might? We did a chilled water plant for a cocoa processing company. They use 160kW motors in their grinders (think: giant blender, with knives that could...well...think: "Charlie and the Chocolate Factory" meets "Saw"...) -- where do you think all that energy goes? The cocoa goes into the grinder at 100-110F and leaves at 140-160F. The cocoa acutally acts as a coolant for the grinder. The rest of the heat is absorbed by jacket water or dissipated into the room (they keep it at 110F year-round to keep the cocoa liquid). When they were commissioning the plant, they had a flow problem and the cocoa in one of the grinders actually caught fire.

http://www.wiener.nl/CocoaLiquor/Index.asp
 
Last edited by a moderator:
  • #12
Quick answer... It does. Even if you stick your finger into a glass of water that is perfectly matched to your body temperature and stir it, the water is hotter. If you want to boil it, just stir faster...lol. BTW, stirring a cup of coffee with your finger will work, but is incredibly inefficient, not to mention painfull.
 
  • #13
Speaking of accelerating liquids causing rises in temperatures, if you have connect the input to the output of a high head pump you can heat up the water and destroy the pump rather quickly.
 
  • #14
Danger said:
Orientation is simply a matter of putting a 'tail' on the nacelle.

well, something is twisting the vertical drive shaft, and because it is doing work, there has to be a resisting torque to that twist. two every (rotational) action there is an equal and opposite reaction. what would otherwise be a freely rotating platform (that would, if there were no other torques, orient the windmill to point to the wind) now has a shaft trying to turn it. it needs to have an opposite torque and the tail wouldn't be enough.

i think it needs two vertical shafts turning in opposite senses to cancel the torrques allowing for the wind and the tail to orient the windmill.
 
  • #15
Danger said:
Bevel gears are probably more efficient than a cable. Hypoids would keep it fairly quiet, as well. Orientation is simply a matter of putting a 'tail' on the nacelle.
What the hell do beets have to do with this? They're one of the most disgusting vegetables on the face of the planet.

Put a little sugar on them. Helps the vegetable go down.
 

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