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Heat and energy

  1. Feb 21, 2014 #1
    1. The problem statement, all variables and given/known data

    Rubbing your hands together warms them by converting work into thermal energy. If a woman rubs her hands back and forth for a total of 10 rubs a distance of 7.50 cm each and with a frictional force averaging 45.0 N, what is the temperature increase? The mass of tissue warmed is only 0.100 kg, mostly in the palms and fingers.

    2. Relevant equations

    work = force * distance

    3. The attempt at a solution

    i can find the work, but after that I don't know how to connect that to temperature change.
     
  2. jcsd
  3. Feb 21, 2014 #2
    Some of the work is converted to heat, I would go with Q = cmΔT , but I have no idea what c is for human skin, tissue, cells or whatever. If you assume the process is 100% efficient, all the work done goes toward heating the skin, then all you would need is the c , the amount of energy it takes to heat up 1 kg of mass by 1 K
    It is said lots of it in our body is water, the c for water is 4.2 kJ/ kgK, the surface of the skin is sweat so water again, but I'm not a beauty salon worker :/, can't help you any further at the moment.
     
    Last edited: Feb 21, 2014
  4. Feb 21, 2014 #3

    adjacent

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    Gold Member

    Hi Naruto,
    Specific heat capacity of human body on average is 3470 J/(kg⋅°C).So I think you should use that.
     
  5. Feb 21, 2014 #4
    so does all the work convert to heat?
     
  6. Feb 21, 2014 #5
    Never does. There is no further data on the assignment, therefore I can assume the process is 100% efficient.
     
  7. Feb 21, 2014 #6
    Thanks guys I got it.
     
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