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Notation for work done

  1. Jul 2, 2010 #1
    My mechanics lecturer uses W for work done. My thermodynamics lecturer uses [tex]\Delta\x[/tex]When asked about this, I have been told that W actually refers to energy. I am not sure whom to believe.

    Also, in mechanics W is the work done by the system on the surroundings. In thermodynamics, work is defined the other way round. Why is that so? Won't that lead to mathematical errors when we use concepts from both branches to solve problems?

    Thanks in advance for any help!
     
  2. jcsd
  3. Jul 2, 2010 #2
    It's true that work is energy. Whether you represent it with "W" or a "Q" or a "[tex]\zeta[/tex]" or a ":tongue2:" or whatever, you measure it in Joules (or some other unit of energy). As far as work being defined as "on the system, by the surroundings" or the reverse, it doesn't really matter. You just have to understand what's going on in the problem to get your signs right. If I lift a boulder to the top of a hill, I have lost chemical energy, and the boulder has gained an equal amount of potential energy. I have done x joules of work on the boulder. Or, if you want, the boulder has done -x joules of work on me. You can use it however you like, so long as you're consistent. Sometimes, teachers make definitions more specific than they need to be, for simplicity's sake. Like always putting the x axis in the direction of motion and the y axis along the normal force. You don't have to do that.
    Just think your signs through. If you're asked to find the work done on a gas when a piston pushes in, you should have a positive answer, etc.
     
  4. Jul 2, 2010 #3
    Nice ":tongue2:" Archosaur...

    :wink:
     
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