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Homework Help: Does turning a spoon in water raises the temperature?

  1. Nov 9, 2015 #1
    1. The problem statement, all variables and given/known data
    I read about Joule's experiment proving the transformation of mechanical work into heat. But say I have a bowl with some water, and I start turning a spoon in it very fast, thus doing work - the water won't get hotter! What am I missing?
    2. Relevant equations
    conservation of energy
    3. The attempt at a solution
    I think maybe the work will simply go to movement and not to heat, but then how do you explain Joule's experiment?
  2. jcsd
  3. Nov 9, 2015 #2


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    Staff: Mentor

    How did you determine that your stirred water didn't get hotter? Did you measure the temperature of the water in your bowl with a sufficiently accurate thermometer? What is "sufficient"? How much heat would you have to put into the water in order for you to see a measurable change in the temperature? What's your estimate of the energy you put into the water by stirring? Was the bowl sufficiently insulated to prevent heat escaping before you could see its effects? Did you characterize all the ways heat could move from the bowl to its surroundings? How about heat conducted by the spoon to or from your hand?

    In what ways does Joule's apparatus differ from your bowl & spoon experiment? What steps did Joule take to minimize or damp bulk motion of the water? Did you do the same?
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