# Heat and energy

1. Feb 21, 2014

### narutoish

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. Feb 21, 2014

### lendav_rott

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
3. Feb 21, 2014

Hi Naruto,
Specific heat capacity of human body on average is 3470 J/(kg⋅°C).So I think you should use that.

4. Feb 21, 2014

### narutoish

so does all the work convert to heat?

5. Feb 21, 2014

### lendav_rott

Never does. There is no further data on the assignment, therefore I can assume the process is 100% efficient.

6. Feb 21, 2014

### narutoish

Thanks guys I got it.