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second law of Thermodynamics?

 
 
Reply Thu 23 Oct, 2008 06:52 pm
Suppose a pregnant rabbit is placed in a sealed capsule with food, water and oxygen and CO2 dispersal equipment. The capsule is weighed just before it is launched into space.

On return from Space about 2 months later, two baby rabbits are present plus the mother.

What is the change in weight of the capsule? What physical law is illustrated by this question?
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Type: Question • Score: 3 • Views: 868 • Replies: 5
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rosborne979
 
  1  
Reply Thu 23 Oct, 2008 07:18 pm
@drlarry01,
Is the co2 dispersed into space or is it contained in the capsule?
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Mr Stillwater
 
  1  
Reply Thu 23 Oct, 2008 07:33 pm
@drlarry01,
The second law states that energy can't be created or lost, only converted into a different form. If the capsule was a sealed environment and nothing - not even sunlight or electricity derived from sunlight intruded - there would be no change in the mass of the capsule.

What would have changed was that the energy present had been degraded ie entropy had increased. This would be in the form of heat produced as the animals respired. The second form would be found in the conversion of the calories in the feed into a low-value waste-product. Without the addition of more electrical energy or calorific inputs the system would degrade to the point that it would not longer support life.

Its mass would not change.
Thomas
 
  2  
Reply Thu 23 Oct, 2008 07:37 pm
@Mr Stillwater,
Mr Stillwater wrote:
The second law states that energy can't be created or lost, only converted into a different form.

That's actually the first law of thermodynamics. The second law of thermodynamics is the one that states that enthropy in a closed system can never decrease.
patiodog
 
  1  
Reply Thu 23 Oct, 2008 07:45 pm
I'm assuming some small amount of dust was accumulated on the capsule and therefore the mass increased by a miniscule amount, according to the law of "even space needs some sweeping up."

Probably not going to get you full credit, though.
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Mr Stillwater
 
  1  
Reply Sat 25 Oct, 2008 01:16 am
@Thomas,
Quote:
That's actually the first law of thermodynamics. The second law of thermodynamics is the one that states that enthropy in a closed system can never decrease


Correct, correct. I was a little bit pre-occupied with the concept of how entropy would be expressed via rabbits (I have issues.... you can check on the appropriate threads).

Entropy will increase, but it can't be 'reset' without the addition of more energy in the form of sunshine or food.
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