Laws of Thermodynamics

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Laws of Thermodynamics

The laws of thermodynamics in action

HowStuffWorks

The British physicist and novelist C.P. Snow once said that a nonscientist who didn't know the second law of thermodynamics was like a scientist who had never read Shakespeare [source: Lambert]. Snow's now-famous statement was meant to emphasize both the importance of thermodynamics and the necessity for nonscientists to learn about it.

Thermodynamics is the study of how energy works in a system, whether it's an engine or the Earth's core. It can be reduced to several basic laws, which Snow cleverly summed up as follows [source: Physics Planet]:

  • You can't win.
  • You can't break even.
  • You can't quit the game.

Let's unpack these a bit. By saying you can't win, Snow meant that since matter and energy are conserved, you can't get one without giving up some of the other (i.e., E=mc²). It also means that for an engine to produce work, you have to supply heat, although in anything other than a perfectly closed system, some heat is inevitably lost to the outside world, which then leads to the second law.

The second statement -- you can't break even -- means that due to ever-increasing entropy, you can't return to the same energy state. Energy concentrated in one place will always flow to places of lower concentration.

Finally, the third law -- you can't quit the game -- refers to absolute zero, the lowest theoretical temperature possible, measured at zero Kelvin or (minus 273.15 degrees Celsius and minus 459.67 degrees Fahrenheit). When a system reaches absolute zero, molecules stop all movement, meaning that there is no kinetic energy, and entropy reaches its lowest possible value. But in the real world, even in the recesses of space, reaching absolutely zero is impossible -- you can only get very close to it.

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