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Chapter C10

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

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

  2. 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 18th century.

  3. 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.

  4. 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)

  5. Caloric today • Caloric (heat energy) absorbed/released is given as = mcΔT where 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

  6. What is heat energy? • Heat energy is kinetic energy of the molecules • The average kinetic energy per molecule is 3/2 kBT • kB 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.

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

  8. 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?

  9. 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

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

  11. Pre-lab • A hot metal cylinder of mass Mcy is added to Mw grams of water in a can of mass Mc. • Write the principle for what happens to the energy in this problem can Metal cylinder Heatenergy Water

  12. Write the following energy equations • Write the equation for the energy lost by the cylinder: • Consider the specific heat of the cylinder to be ccy, that of the water and the can to be cw and cc. The initial temperature of the cylinder is Tcy, the initial temperature of the water and the can is Ti. The final equilibrium temperature is Tf.

  13. Write the equation for the energy gained by the water and can. • ΔUwater=Mwcw(Tf-Ti) • ΔUcan=Mccc(Tf-Ti) • 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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