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Re-added zeroth law section, not sure wh yit was removed
James Joule in 1849 made a precise determination of the mechanical equivalent of heat into work. His stirring of water in a pot (work input with a mechanical stirring rod, caused by the motion of a 1-kg weight falling 42.4 cm) caused a temperature increase (heat output); his homemade, yet very-precise thermometers recorded the conversion factor. The unit of energy is now called the ''[[International_System_of_Units#Joule|joule]]''. 4.2 joules of energy can raise one gram of water 1 degree Celsius, an amount called one calorie. (The large-C "Calorie" used in nutritional measure is 1000 small-c calories.)
James Joule in 1849 made a precise determination of the mechanical equivalent of heat into work. His stirring of water in a pot (work input with a mechanical stirring rod, caused by the motion of a 1-kg weight falling 42.4 cm) caused a temperature increase (heat output); his homemade, yet very-precise thermometers recorded the conversion factor. The unit of energy is now called the ''[[International_System_of_Units#Joule|joule]]''. 4.2 joules of energy can raise one gram of water 1 degree Celsius, an amount called one calorie. (The large-C "Calorie" used in nutritional measure is 1000 small-c calories.)
==Zeroth Law of Thermodynamics==
The zeroth law was formulated after the first and second laws, but is more fundamental, so was named "zeroth" as to avoid renumbering the other laws. It can be stated in terms of three systems, A, B and C. It states that if A is in thermal equilibrium with B, and B is in thermal equilibrium with C, then A must also be in thermal equilibrium with C. It allows us to define [[temperature]]. By bringing one body (our thermometer) into contact with another body, eventually they will reach thermal equilibrium and be at the same temperature. If we can measure a physical property of our thermometer such as its length and know how that varies with temperature, we can calculate the temperature of the body in question.
==[[First Law of Thermodynamics]]==
==[[First Law of Thermodynamics]]==