1. PF Contest - Win "Conquering the Physics GRE" book! Click Here to Enter
    Dismiss Notice
Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Entrophy question

  1. Dec 10, 2003 #1
    Entropy question

    I've got myself all confused, I don't even know if my question makes sense. But here it goes: If you have a container with X molecules just bouncing around like usual, and a container with X molecules, but none of them move, they only spin in place, which container has more entropy?
    Last edited: Dec 10, 2003
  2. jcsd
  3. Dec 10, 2003 #2
    I believe it to be the one with the particles moving around the container. as entropy is chaos.
  4. Dec 10, 2003 #3
    That is what I thought, because it seems like even though the molecules in one box spin, they don't hit anything and so it would seem like they are very cold/low entropy, but I really don't trust myself, because technically the molecules still have kinetic energy, it is just going around in circles.
    Are there any differing opinions?
    Last edited: Dec 10, 2003
  5. Dec 10, 2003 #4


    User Avatar
    Science Advisor

    kinetic energy is not directly connected to entropy. Entropy is closer to being a measure of disorder and a bunch of molecules sitting in fixed positions is about as ordered as you can get!

    (I said "closer to" because I I said "Entropy is disorder" I would get jumped on with both feet!)
  6. Dec 11, 2003 #5
    I understand, it is easy to get confused, because when I think of thermodynamics I think of gases, and cold gases are by definition orderly and have a low average kinectic energy.
    So you agree then, the spinning in one spot molecules have less entropy than the bouncing all over ones.
  7. Dec 11, 2003 #6
    I've tried to PM HallsofIvy twice, and don't know if I'm filling up his inbox more than it says it is, so I will just ask here, though it is slightly off topic. Can one draw a literal analogy between the molecules above and a small closed system of balls? If we had, say 10, balls bouncing around in a closed system, would that system have more entropy than a closed system of 10 balls just sitting and spinning in place?
  8. Dec 11, 2003 #7


    User Avatar
    Science Advisor

    Yes, balls flying around a room have more entropy than balls sitting in one location. The more random the "flying", the more entropy.
    (Apparently I haven't been deleting private messages. Now, if I can just figure out HOW to do that!)
  9. Dec 11, 2003 #8
    Good, thank you.
  10. Dec 13, 2003 #9
    check out my "Maxwell's Demon" post about entrophy and give your suggestions.
  11. Dec 13, 2003 #10
    You are making more out of entropy than it is. Entropy is only disorder.

    Hold a glass in your hand - that has a relatively low entroypy. Drop the glass on the floor - that has a higher entropy. If you take those broken peaces of glass and start shaking them up they have even a greater entropy, ect......

  12. Dec 14, 2003 #11
    Imagine entropy most simply as states (i. e., all possible arrangements) of a given physical system. Introducing a degree of freedom like linear velocity dependent kinetic energy should increase entropy due to the added configurations of states. (For an ideal gas, each degree of freedom for spin, linear velocity or rotation contributes kT/2 in energy.)
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook

Similar Threads - Entrophy question Date
Energy in a Magnetic Field (SMES Core Question) Today at 10:28 AM
I Laser Safety Glasses question Wednesday at 7:02 PM
I Question about lifting water through a water pipe Mar 13, 2018
I MRI physics question Mar 13, 2018