# Joules in a Calorie

1. Jun 25, 2012

### Dunce

I can find the conversion easy enough, but I want to understand the fundamentals behind it. How do we KNOW that 4.184 J are in a cal? I'm learning thermodynamics and my book neglects to mention this(yet), and I'm getting hung up on it.

I am having difficulty understanding how temperature translates into work this way. Temperature is the average kinetic energy of the system, I can see how they are related, but I'm just not understanding how you can experimentally show that 4.184 kg m2/s2 would raise the temperature of 1g of water 1°C.

2. Jun 25, 2012

### Staff: Mentor

3. Jun 26, 2012

### Andrew Mason

Temperature is a statistical average of the translational kinetic energy of the molecules.

One way to do this would be to pass an electric current through a heating coil to heat water. That is what your kettle does. If you pass 1 ampere at 120 volts through the coil for 1 second, you will add 120 J. to the water. If you also have an ammeter and a measuring cup you should be able to do the experiment with your own kettle.

AM