Lecture214Week9

Lecture214Week9 - This Week Heat and Temperature Water and...

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This Week Heat and Temperature Water and Ice Our world would be different if water didn’t expand Engines We can’t use all the energy! Why is a diesel engine more efficient? Geysers: You have to be faithful 12/09/11 Physics 214 Fall 2011 1
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12/09/11 Physics 214 Fall 2011 2 Heat Heat is a form of energy and any object has internal energy in the form of kinetic energy of the atoms or molecules and in potential energy connected with the molecular structure and the electromagnetic forces among the constituents. If we add energy to an object the internal energy increases. Energy can be added in many ways. For example we can do work such as the frictional forces on a moving object. electromagnetic radiation from the sun. a source of heat like a hair dryer.
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12/09/11 Physics 214 Fall 2011 3 First Law of Thermodynamics The increase in the internal energy of a system is equal to the amount of heat added to the system minus the amount of work done by the system. U = internal energy Q = heat that is added or removed W system = is the work done by the system Looking at the pictures you can see that the force pushing on the piston does positive work and therefore is putting energy into the gas. The work done by the gas is negative because the force the piston exerts is to the right and the movement of the piston is to the left. ENERGY CONSERVATION ΔU = Q – W system or ΔU = Q + W external
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12/09/11 Physics 214 Fall 2011 4 Temperature Heat flows from a hot body to a cold body until they reach thermal equilibrium. Temperature is the quantity that measures whether one body is hotter than another and at thermal equilibrium both bodies have the same temperature. The simplest picture is a gas of free molecules where the energy is kinetic. A higher temperaturemeans higher velocities and more stored energy. Increase U and T increases http://jersey.uoregon.edu/vlab/Thermodynamics/index.html http://www2.biglobe.ne.jp/~norimari/science/JavaApp/Mole/e-gas.html
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12/09/11 Physics 214 Fall 2011 5 Measuring temperature Physical properties of an object change with temperature. For example mercury expands as the temperature increases and we can use that expansion to measure T. There are three temperature scales, Celsius, Fahrenheit and Kelvin Mixture of ice and water 0 0 C 32 0 F 273 0 K Boiling point of water 100 0 C 212 0 F 373 0 K T c = 5/9(T f – 32) T f = 9/5T c + 32 T K = T c + 273 Note that the temperature at which water boils depends on the value of the atmospheric pressure so that at higher altitudes water boils at a lower temperature
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12/09/11 Physics 214 Fall 2011 6 Absolute zero An ideal gas obeys the law PV = constant x T if we keep V constant the pressure is proportional to T. If we
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Lecture214Week9 - This Week Heat and Temperature Water and...

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