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Chapter C10 Thermal Energy B.5, B.6, S.1, S.5 - Due Friday

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Caloric (Explaining where heat comes from) A colorless, orderless liquid that is in most substances. When a substance burns the caloric in it is given off as heat This theory explained heat until the 18 th century.

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Benjamin Thompson An American who fled the U.S. in 1773 because of British sympathies. Became a military consultant (mercenary) Took the name of Count Rumford Made cannon Discovered that heat is a form of energy Set up the first public school for the children of his workers.

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Benjamin Thompson 1 calorie is the amount of heat necessary to raise the temperature of one gram of water one degree Celsius. James Prescott Joule showed how many joules (unit of energy) were in a calorie (unit of heat). 1 calorie = 4.186 joules (put on formula sheet)

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Caloric today Caloric (heat energy) absorbed/released is given as = mcΔTwhere m = mass c = constant that depends on the substance (called specific heat) ΔT = change in temperature caused by the addition/release of the caloric (heat) For water c=1 cal · g -1 · (Cº) -1

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What is heat energy? Heat energy is kinetic energy of the molecules The average kinetic energy per molecule is 3/2 k B T k B Boltzman’s constant = 1.38 x 10 -23 j/K T is the absolute temperature T=0 when all K.E. is gone from molecules. This is -273º C. This is the Lowest possible temperature.

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Work and heat Hot plate Work (+) Work(-) Heat (+) ice Heat (-) system Heat is energy that flows because of a temperature difference Work is any other type of energy that crosses a boundary.

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Energy that is “lost” often ends up as heat For example in friction, kinetic energy of the center of mass is transformed into the kinetic energy of the energy of the surfaces in contact When a moving object hits something (such as the ground) the energy ends up as heat in the same way. Hit your hand hard on the table, can you feel the heat?

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Internal energy U = internal energy dU=McdT dU is the change in internal energy M is the mass c is the specific heat (see page 183) dT is the temperature change For a finite temperature change this becomes: ΔU=Mc ΔT

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Problems due Monday B.5, B.7, S.1, S.5 –Due Friday Lab for Tuesday = Begin new lab set.

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Pre-lab A hot metal cylinder of mass M cy is added to M w grams of water in a can of mass M c. Write the principle for what happens to the energy in this problem Metal cylinder Heat energy can Water

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Write the following energy equations Write the equation for the energy lost by the cylinder: Consider the specific heat of the cylinder to be c cy, that of the water and the can to be c w and c c. The initial temperature of the cylinder is T cy, the initial temperature of the water and the can is T i. The final equilibrium temperature is T f.

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Write the equation for the energy gained by the water and can. ΔU water =M w c w (T f -T i ) ΔU can =M c c c (T f -T i ) In your lab you will measure and know everything except the specific heat of the cylinder. Set the above equations equal and solve for the specific heat of the can.

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