# 2nd law of thermodynamicsWatch

#1
Ok so i have learnt this as part of A-level physics but there seems to be a different definition everywhere!

the heat engine version states
" No continually working heat engine can take heat from a source and convert it completely into work"

the heat-pump version says that
" heat cannot be transferred continually from one body to another at a higher temperature unless work is done by an external agent"

Then there is the whole thing which states that the entropy of the universe always increases, with entropy being defined as the meausre of disorder.

If you were to define the 2nd law, how would you do it concisely?

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9 years ago
#2
(Original post by sonic23)
Ok so i have learnt this as part of A-level physics but there seems to be a different definition everywhere!

the heat engine version states
" No continually working heat engine can take heat from a source and convert it completely into work"

the heat-pump version says that
" heat cannot be transferred continually from one body to another at a higher temperature unless work is done by an external agent"

Then there is the whole thing which states that the entropy of the universe always increases, with entropy being defined as the meausre of disorder.

If you were to define the 2nd law, how would you do it concisely?

dS dt >0
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9 years ago
#3
heat generally cannot spontaneously move from a lower temperature body to a body with higher temperature body
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9 years ago
#4
Heat cannot of itself move from a cold body to a hotter body. There are lots of different statements - it can be proven that they are identical.
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9 years ago
#5
(Original post by sonic23)
Ok so i have learnt this as part of A-level physics but there seems to be a different definition everywhere!

the heat engine version states
" No continually working heat engine can take heat from a source and convert it completely into work"

the heat-pump version says that
" heat cannot be transferred continually from one body to another at a higher temperature unless work is done by an external agent"

Then there is the whole thing which states that the entropy of the universe always increases, with entropy being defined as the meausre of disorder.

If you were to define the 2nd law, how would you do it concisely?

Flanders and Swann put it quite succinctly: http://uk.youtube.com/watch?v=Cb2kBFqrZx8
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9 years ago
#6
Aaah, flanders and swann. We had that played in our lectures.
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#7
(Original post by motoroller)
Aaah, flanders and swann. We had that played in our lectures.
please dont tell me anyone found it funny
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9 years ago
#8
(Original post by sonic23)
funny
The lecturer got a standing ovation at the end of his lecture course.
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9 years ago
#9
OP, if u think about it carefully, they all mean the same thing, the entropy of the universe increases over time.
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9 years ago
#10
(Original post by wizz_kid)
OP, if u think about it carefully, they all mean the same thing, the entropy of the universe increases over time.
he probably realises that but just wants to know how to express it in a simple yet understandable form i guess?
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