What Happens When U, Q, and W Are Negative in the First Law of Thermodynamics?

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SUMMARY

The discussion focuses on the implications of negative values for internal energy (U), heat transfer (Q), and work done (W) in the context of the first law of thermodynamics, represented by the equation dU = Q - W. When U, Q, and W are negative, it indicates that the system is losing internal energy, leading to a decrease in temperature, such as water freezing. Specifically, a negative dU signifies energy loss, while a negative Q indicates heat is being supplied to the surroundings, and a negative W means the system performs negative work, equating to positive work done on the system.

PREREQUISITES
  • Understanding of the first law of thermodynamics
  • Familiarity with thermodynamic variables: internal energy (U), heat (Q), and work (W)
  • Basic knowledge of thermodynamic processes, including heating and cooling
  • Concept of energy conservation in closed systems
NEXT STEPS
  • Study the implications of negative work in thermodynamic systems
  • Explore the relationship between temperature changes and internal energy loss
  • Learn about phase changes in thermodynamics, particularly freezing
  • Investigate real-world applications of the first law of thermodynamics in engineering
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Students of thermodynamics, physics enthusiasts, and professionals in engineering fields seeking to deepen their understanding of energy transfer and thermodynamic principles.

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Homework Statement


I am looking into the first law of thermodynamics.
But I'm not sure with some parts.

Homework Equations


dU=Q-W What does it mean when U Q and W are negatives.
Also solids with W=0

The Attempt at a Solution


So the equation will change to -U=-Q+W
Does it lose it's internal energy?
 
Last edited:
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It's

dU = \delta Q - \delta W

If dU is negative that means that the system loses internal energy. The temperature goes down, or water freezing etc.

if \delta Q is negative, the system supplies heat to its surroundings.

if \delta W is negative, the system does negative work on its surroundings, this is the same as positive work done on the system
 

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