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Defining Heat

Holt Physics, Chapter 10 Section 2. Defining Heat. Heat and Energy. Heat – energy transferred between objects because of a difference in their temperatures. It is helpful to shift attention to the behavior of atoms and molecules.

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Defining Heat

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  1. Holt Physics, Chapter 10 Section 2 Defining Heat

  2. Heat and Energy • Heat – energy transferred between objects because of a difference in their temperatures. • It is helpful to shift attention to the behavior of atoms and molecules. • Mechanics can be used to explain much of what is happening at the molecular, or microscopic, level. • This in turn accounts for what you observe at the macroscopic level.

  3. Energy is transferred between substances as heat. • Macroscopic viewpoint: always from higher to lower temperature. • The direction of heat travel can be explained at the atomic level.

  4. Higher temperature juice has higher avg. KE than the water. • Collision of particles transfers energy from high to low. • Net transfer continues until avg. KE is the same between the juice and the water. • With same avg. KE, juice and water at thermal equilibrium (i.e., at the same temperature).

  5. The transfer of energy as heat alters and object’s temperature. • When two object are in thermal contact, there is no net gain or loss of energy, even though energy is transferred. • Difference between heat and temperature.

  6. The amount of heat transferred depends on the temperature difference between the two objects. • Greater the difference, greater the amount of energy transferred as heat. • Concepts of heat and temperature can help explain hot and cold sensation.

  7. Because heat, like work, is energy in transit, all heat units can be converted to joules (J) • Heat is symbolized with the letter Q.

  8. Heat and Work • Hammer nail into wood, then pry out. • Nail feels hot. • Work done on nail was resisted by friction. • Friction increases internal energy of nail  temp. increases. • Temperature difference between hand and nail results in transfer of heat. • Deforming solids can increase internal energy.

  9. Total energy is conserved • Not all work done to overcome fiction is converted to mechanical energy. • If changes in internal energy are taken into account, along with changes in mechanical energy, energy in a closed system is a conserved property

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