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Thermal Energy
Atomic Motion   The macroscopic properties of a system are based    on the microscopic behavior of atoms.    Macroscopic ...
Ideal Gas Energy   Kinetic theory supplies the    energy for an ideal gas.     • Kav = (3/2)kT   Convert this to the tot...
Internal Energy                        The kinetic energy of an                         ideal gas is its internal        ...
Vibrations                               Mean particle speed is not                                the only source of int...
Energy Transfer                     Thermal energy changes in                      a system.                      • It fl...
Heat and Work   Work is a process that            Heat is a process that    represents the change in the       represent...
Mechanical Equivalent   In the 1800’s James Joule    demonstrated that    mechanical work could    cause a change in    t...
Calorie   Heat was measured by a                Since SI has a unit of energy    change in temperature.                 ...
Burn It   You gobble too much ice            Convert to joules from kcal.    cream and decide to walk up          • W = ...
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P210 13a

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P210 13a

  1. 1. Thermal Energy
  2. 2. Atomic Motion The macroscopic properties of a system are based on the microscopic behavior of atoms. Macroscopic Microscopic equation of state: laws of motion: pressure, position, volume, velocity, temperature energy
  3. 3. Ideal Gas Energy Kinetic theory supplies the energy for an ideal gas. • Kav = (3/2)kT Convert this to the total system energy. • U = (3/2)NkT • U = (3/2)nRT Energy based on temperature and This energy is internal to the number of molecules gas.
  4. 4. Internal Energy  The kinetic energy of an ideal gas is its internal energy. • Also called thermal energy vCM  Internal energy does not include energy from external measures. • Center of mass translation • Rigid body rotation Fext • Potential from external force
  5. 5. Vibrations  Mean particle speed is not the only source of internalRotation energy.around centerof mass  Real molecules can have internal motion. • Rotation • Vibration  These effects add to internal energy. Vibration at center of mass
  6. 6. Energy Transfer  Thermal energy changes in a system. • It flows in and out • Due to changes in macroscopic properties Heat flow  When it is due to temperature changes it is called heat.
  7. 7. Heat and Work Work is a process that  Heat is a process that represents the change in the represents the change in the mechanical energy. thermal energy. • Force acting through a • Due to a difference in distance temperature • Measured in joules like • Measured in joules like energy energy
  8. 8. Mechanical Equivalent In the 1800’s James Joule demonstrated that mechanical work could cause a change in temperature. Heat, like work, represented a change in energy.
  9. 9. Calorie Heat was measured by a  Since SI has a unit of energy change in temperature. (J) it remains the unit for all • 1 calorie (cal) is the amount forms of energy. of heat needed to raise 1 g • Work of water by 1 °C. • Mechanical energy • 1 kcal = 1000 cal, and is • Potential energy what we call a “Calorie” for • Dissipative energy food. • Heat • Thermal energy Calories (or kcal) are often • Internal energy used to measure heat or internal energy.  1 cal = 4.186 J
  10. 10. Burn It You gobble too much ice  Convert to joules from kcal. cream and decide to walk up • W = (500 kcal)(1000 stairs to burn the additional cal/kcal)(4.186 J/cal) 500 Calories. • W = 2.1 x 106 J. If your mass is 60 kg, what  Work climbing is W = mgh. vertical height must you • h = W / mg = (2.1 x 106 J) / climb? (60 kg)(9.8 m/s2) • h = 3600 m.  Real humans are inefficient and h is closer to 700 m. next

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