Lecture_22

# Lecture_22 - This is what we mean by heat: It is a measure...

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This is what we mean by heat : It is a measure of the total internal energy of an object. eat is transferred between two objects that have different temperatures. Heat is transferred between two objects that have different temperatures. It “flows” from the hotter object to the colder object. As heat flows from the hot object to the cold object, that means that the internal jj , energy of the hot object decreases, and the internal energy of the cold object increases. Heat can flow from one object to another, but an object does not have or contain heat. An object has an internal energy. It wasn’t until the mid 19 th century that scientists recognized the flow of heat as an exchange of internal energy. Before, they thought of it as an invisible fluid called “caloric”. They defined heat in terms of the temperature change it produced in an object. he traditional unit of heat is the alorie (cal) Lower-case c The traditional unit of heat is the calorie (cal) It is the amount of “heat” needed to raise 1 gram of water by 1 o C. 1 kcal = 1000 cal 1 btu = 0.252 kcal

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The calories marked on food are actually kcal, or “Big Calories”. 1 Cal = 1000 cal The more massive an object is, the more heat that is required to change its temperature, and the greater the change in temperature of an object, the greater the heat that is required. This leads to the following relationship: T cm Q Δ = In words, this says that Q is the amount of heat that must be added or removed from an object of mass m to change its temperature by an amount Δ T . j gp y The proportionality constant, c , is called the specific heat capacity, or just specific heat. c is the heat necessary to raise the temperature of 1 kg of material by 1 o C. Thus, c is material dependent, and it has units of [J/kg· o C].
We can raise the temperature of an object by adding heat to it, which means increasing the internal energy of the object. But we know that energy is equivalent to work. Thus, we should be able to do work on an object nd raise its temperature and raise its temperature.

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## This note was uploaded on 09/25/2011 for the course PHYS 2002 taught by Professor Blackmon during the Spring '08 term at LSU.

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Lecture_22 - This is what we mean by heat: It is a measure...

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