# Heat - Heat We saw that when two bodies are not in thermal equilibrium and are in contact with each other the temperatures of the objects changes

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Heat We saw that when two bodies are not in thermal equilibrium and are in contact with each other, the temperatures of the objects changes until equilibrium is established. Obviously some sort of interaction takes place, and as in all interactions, something is exchanged between the two systems. That something is heat . We call the exchange of heat between the two systems heat transfer . Heat transfer has been shown via experiments by Rumford and Joule to be an energy transfer between the systems. We define heat transfer as energy transfer that takes place solely because of a temperature difference . This does not mean that heat transfer is the only method of transferring energy. We have seen many examples of other forms of energy transfer throughout this course. The unit of the quantity of heat transferred with reference to the temperature change of any particular material is called the calorie. It is defined to be the amount of heat required to heat one gram of water from 14.5°C to 15.5°C. Since heat is really energy transfer, we can relate the calorie to the joule, and experimentally we find that 1 cal = 4.186 J What happens when a heat is transferred to an object of mass m ? We expect that the temperature will rise. The amount that the temperature changes should also depend on the mass of the object; it takes more heat to change the temperature of a massive object than of a non-massive object. This lets us write dQ = cmdT (20.1) where dQ is the amount of heat added and c is a constant of proportionality. It varies from material to material, and is called the

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## This note was uploaded on 07/24/2009 for the course PHY 092342 taught by Professor Knott during the Spring '09 term at Cosumnes River College.

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Heat - Heat We saw that when two bodies are not in thermal equilibrium and are in contact with each other the temperatures of the objects changes

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