What's the relation with Gravity & Laws of Thermodynamics

  • #1
Here's a thought from other thread
Gravity have been keeping us firmly on the ground, without gravity we would have been "floating" around, and we never give anything back to gravity.

A reply
As we go about our business in the earth gravity well we are constantly shifting between potential energy and kinetic energy and generating heat energy as a result. We don't get a free lunch and we don't violate the laws of thermodynamics.

So what's the relation between gravity and the laws of thermodynamic, or should it be conservation of energy?
 

Answers and Replies

  • #2
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The fact that the density of the air particles as we go up becomes smaller and smaller is the effect of thermodynamics on gravity. Low energy states are populated more by particles than high energy states. Also heating up of atmosphere due to radiation and friction is also due to thermodynamic principle. As such there is no direct relation. Gravitational force acts on every molecule of air but thermodynamic principles apply to macroscopic variables which have meaning for aggregates of molecules. Pressure, temperature, density are such variables.

Conservation of energy is a general principle applicable everywhere even in thermodynamics. But principle of increase of entropy of universe as whole or what you designate as Universe in a local manner is a valid principle which is obeyed is a principle applicable only in the field of thermodynamics.
 
  • #3
The fact that the density of the air particles as we go up becomes smaller and smaller is the effect of thermodynamics on gravity.
What about the effect of thermodynamics on human bones density if gravity is increased by double?
Do you consider gravity doing work by pulling almost every objects onto the surface, and how does thermodynamics or conservation apply in this situation?
 
  • #4
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No free lunch refers to getting something from nothing as would happen if perpetual motion machines were real. We as a machine must convert chemical energy which we've accumulated from eating, breathing and drinking into kinetic energy of motion in order to counteract gravity. The byproduct of this conversion is heat.

I would suggest everyone here read Benjamin Crowell's book on Conceptual Physics:

http://lightandmatter.com/cp/

before discussing this matter further.

Since there is nothing more to say then this thread is now closed.
 
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