Does Work Depend on the Displacement of an Object?

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    Evaporation Heat
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Discussion Overview

The discussion revolves around the concept of work in physics, specifically whether work is done when a system absorbs energy during processes such as evaporation and compression. Participants explore the definitions and conditions under which work is considered to occur, with a focus on the relationship between force, displacement, and energy absorption.

Discussion Character

  • Conceptual clarification, Debate/contested, Homework-related

Main Points Raised

  • Some participants propose that both evaporation and compression involve energy absorption, questioning the distinction made in the answer key.
  • Others argue that evaporation does not involve work because there is no force acting over a displacement in that process.
  • A participant suggests that while energy is absorbed during evaporation, the system (water) may cool down, implying a different energy transfer mechanism.
  • Definitions of work are discussed, emphasizing that work requires a force acting over a distance, with examples illustrating when work is done versus when it is not.

Areas of Agreement / Disagreement

Participants do not reach a consensus on whether work is done during evaporation, with competing views on the definitions and conditions for work being presented.

Contextual Notes

There are unresolved assumptions regarding the definitions of work and energy transfer in different processes, as well as the implications of cooling in the context of energy absorption.

cp255
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Homework Statement


For which process does the system absorb energy in the form of work?
a) Water Evaporates into steam.
b)Air is compressed by a bicycle pump.
c) Both


Homework Equations





The Attempt at a Solution



I though the answer was both. However, the key says the correct answer was just B. Why would it not be A as well? I thought evaporation required the input of energy.
 
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Work is a specific form of energy. While (a) needs energy, it will not use work.
 
I was thinking that maybe although the energy went into the steam they system is the water which would have cooled.
 
Usually the water will cool down, indeed.
 
So what exactly is work then?
 
Work
A force acting over some displacement. There is no such force or displacement involved in evaporation.
 
cp255 said:
So what exactly is work then?

Force applied over some unit of distance. If you push against a car and it moves, you've done work.

If you push on a wall, and the wall doesn't move or fall over, then you've done no work. The displacement of the wall here is 0. Now if the wall does fall over then you've done work. Good work!

(Or bad)
 

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