Is a Zero Efficiency Machine Possible and Thermodynamically Stable?

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Discussion Overview

The discussion revolves around the concept of a machine with zero efficiency, particularly in the context of motors connected in series where energy losses accumulate. Participants explore whether such a machine can exist and if it can be thermodynamically stable when all input energy is converted to heat.

Discussion Character

  • Exploratory
  • Debate/contested
  • Technical explanation

Main Points Raised

  • Some participants propose that a machine can have zero efficiency if it does not perform useful work, suggesting that energy losses can be maximized through a series of motors.
  • Others argue that friction can serve as a mechanism for achieving zero efficiency in a machine.
  • A participant humorously suggests that using sand instead of gasoline in a car would lead to zero efficiency.
  • Concerns are raised about the diminishing power supply to each subsequent motor, leading to potential failure of the last motor to operate.
  • Some participants mention that while 100% of work can be converted to heat, the reverse is not possible, indicating a distinction between work and heat in thermodynamic processes.
  • There is a discussion about the implications of a machine being thermodynamically stable if it converts all input energy to heat, with some suggesting that this could be viewed as a heater with 100% efficiency in terms of heat output.
  • One participant notes that running a motor without a load could demonstrate the concept of zero efficiency through various losses.

Areas of Agreement / Disagreement

Participants express multiple competing views regarding the feasibility of a zero efficiency machine and its thermodynamic implications. The discussion remains unresolved with no consensus on the definitions or implications of efficiency in this context.

Contextual Notes

Participants highlight limitations in understanding the thermodynamic stability of such a machine, particularly regarding the definitions of efficiency and the conversion of energy forms. There are unresolved questions about the implications of 100% conversion of work to heat and the nature of work and heat as process quantities.

sodaboy7
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Lets say if we have an induction motor or any motor whose rotating shaft acts as a source of alternating emf to another motor and rotating shaft of this motor again acts as a source of alternating emf to third motor and so on... We connect such a finite number of motors and we call it as a single "machine". At each step there will be some losses which will get added up at end and after finite number of such motors all the INPUT ENERGY will be converted into LOSS. The efficiency of such a machine will be zero. Is this possible?? I mean can there be a situation of zero efficiency ?? And if all the energy loss is dissipated as heat then ALL the electrical energy is converted to heat. Is this thermodynamically stable machine?
 
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Efficiency of a machine is simply defined as the useful work out divided by the heat you had to put in. All you need to do to have a zero efficiency machine is make sure it does not useful work.
 
Friction is an excellent zero-efficiency conversion mechanism.
 
Put sand instead of gasoline in your car's gas tank and it will become a zero efficiency machine very quickly.
 
sodaboy7 said:
Lets say if we have an induction motor or any motor whose rotating shaft acts as a source of alternating emf to another motor and rotating shaft of this motor again acts as a source of alternating emf to third motor and so on... We connect such a finite number of motors and we call it as a single "machine". At each step there will be some losses which will get added up at end and after finite number of such motors all the INPUT ENERGY will be converted into LOSS. The efficiency of such a machine will be zero. Is this possible?? I mean can there be a situation of zero efficiency ?? And if all the energy loss is dissipated as heat then ALL the electrical energy is converted to heat. Is this thermodynamically stable machine?

Not sure about the thought of the question, but the supply of power to the first unit would reduce through each of the next units, until the last one received so little power it would likely not turn, but would displace the energy as resistance loss.

"thermodynamically stable machine", I can't quite see the value of that in a context. Can you add more about your thoughts ?
 
I don't think it would have a zero thermal efficiency which is n=1-Tc/Th. If there was no change in tempature than it would be zero percent efficient... which seems rather obvious.
 
RonL said:
Not sure about the thought of the question, but the supply of power to the first unit would reduce through each of the next units, until the last one received so little power it would likely not turn

The last motor will receive almost no power so it won't rotate. Energy at each motor is lost as heat. So if we use this "machine" as a heater, we will get a heater of 100% efficiency! as ALL the input energy is converted to heat energy (in form of loss). This will happen only and only when the efficiency of this machine with respect to mechanical energy is zero. But 100% efficiency is not valid in thermodynamics.
 
I think its a known fact you can convert 100% of work into heat, but you can't convert 100% of heat into work.
 
sodaboy7 said:
Lets say if we have an induction motor or any motor whose rotating shaft acts as a source of alternating emf to another motor and rotating shaft of this motor again acts as a source of alternating emf to third motor and so on... We connect such a finite number of motors and we call it as a single "machine". At each step there will be some losses which will get added up at end and after finite number of such motors all the INPUT ENERGY will be converted into LOSS. The efficiency of such a machine will be zero. Is this possible?? I mean can there be a situation of zero efficiency ?? And if all the energy loss is dissipated as heat then ALL the electrical energy is converted to heat. Is this thermodynamically stable machine?

You can simply run a motor without a load excepting the winding resistance, bearing friction, the hysteresis losses, and other minor things. That's how to do it.
 
  • #10
clearwater304 said:
I think its a known fact you can convert 100% of work into heat, but you can't convert 100% of heat into work.

You can't convert 100% of mass-energy into heat, nor vice-versa.

Work is not something that "converts". Like heat, it is a process quantity, not a substance. "Work" and "heat" both act as verbs in thermodynamics.
 
  • #11
kmarinas86 said:
You can't convert 100% of mass-energy into heat, nor vice-versa.

Work is not something that "converts". Like heat, it is a process quantity, not a substance. "Work" and "heat" both act as verbs in thermodynamics.

I can't look up a reference becuase I'm studying for a final right now, but it's something I heard a few years ago. I was in a physics lab and we were running an expiriment where a a rope turned a pulley when a bucket fell. The pulley had a friction bearing and the TA said this cuased the work to be converted into heat, that you could have 100% conversion of work to heat but not vice versa.
 
  • #12
Thermodynamics is the study of the inter-relation between heat, work and internal energy of a system.

Thanks,
engagement rings
 

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