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You did work against friction, where did the energy go?

You did work against friction, where did the energy go?. Thermal Energy. Thermal Energy. Thermal Energy: The total internal Energy Internal Energy: The sum of the kinetic and potential energies of the internal motion of particles that make up an object. Heat Flow. Warm. Warm.

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You did work against friction, where did the energy go?

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  1. You did work against friction, where did the energy go? Thermal Energy

  2. Thermal Energy • Thermal Energy: The total internal Energy • Internal Energy: The sum of the kinetic and potential energies of the internal motion of particles that make up an object.

  3. Heat Flow Warm Warm What is Heat? • Heat is energy in transfer from an object of higher temperature to one of lower temperature. • The quantity of energy transfer from one object to another is because of a difference in temperature. Cold Hot Thermal Equilibrium

  4. Change of Phase of State • States of matter • Solid • Liquid • Gas • What happens to the temperature when matter is changing states?

  5. C F 100 212 0 32 40 40 Substances in Phase Transfer

  6. D E C B A Phase Change • Between A-B: The ice is warming to 0oC • Between B-C: Thermal energy melts the ice at 0oC • Between C-D: The water is warm to 100oC • Between D-E: The water boils and changes to vapor at 100oC • After E: The temperature of the vapor increases

  7. Thermal Energy Transfer • Conduction: • Transfer of Kinetic Energy by contact • Convection: • Heat transfer by the motion of a fluid (e.g. air) • Radiation: • Electromagnetic waves carry energy Note: Conduction and Convection require matter

  8. Conduction • Conduction is the transfer of heat through molecular collisions. • This form of heat transfer best occurs in solids where molecules are closely packed. • Materials that conduct heat well are called conductors. (Eg. metals such as copper and iron) Magnification

  9. Convection • Convection is the transfer of heat though moving fluids. • A fluid is any substance that flows, which includes all liquids and gases. • Examples include convection ovens and cloud formation. Convection ?

  10. Radiation(not radioactivity) • Radiation is the transfer of heat via electromagnetic waves. • These waves include visible light, but are mostly infrared. • No matter is required for this type of heat transfer. • Examples include the sun’s heat and warmth felt from a flame. Open Space ? Radiation

  11. Heat Transfer Question • Consider a camp fire burning vigorously. • How is heat normally transferred while warming its viewers? • Radiation • How is heat transferred when you put a hand in the smoke? • Convection • How is heat transferred to a stick when it is placed in the hot coals? • Conduction • Some situations involve multiple heat transfer types like this.

  12. Specific Heat Heat: The energy that flows as a result of a difference in temperature Q: The symbol for heat. Measured in Joules (J) C: the symbol for Specific Heat. The amount of energy needed to raise a unit of mass one temperature unit. (J/kg K)

  13. Heat gained Q: Heat m: mass ΔT: Change in Temperature

  14. Sample Heat Problem • How much heat is required to raise the temperature of a 2.4kg gold ingot (c = 129J/kgK) from 23°C to 45°C? Light 2.4kg

  15. Calorimerty Calorimeter: A device used to measure changes in thermal energy. Calorimerty depends on the conservation of energy. Qgained + Qlost = Zero

  16. Calorimerty Example #1 A .4kg block of zinc @115°C is placed in .5kg of water @15°C. Find the final temperature.

  17. Heat of fusion Example #1 If 5,000J is added to ice at 0oC, how much ice is melted? Q=mHf Q=mHv Water Hf=3.34x105J/kg Water Hv=2.26x106J/kg Specific Heat Phase Change

  18. Calorimerty Example example #2 A .1kg block of brass @90°C is placed in .2kg of water @20°C. Find the final temperature.

  19. Heat of fusion example #2 How much heat must be transferred to 100g of ice at 00C unit the ice melts and the temperature of the resulting water rises to 200C? Water Hf=3.34x105J/kg

  20. Heat TransferExample 1 A 0.40kg block of iron is heated from 295K to 325K. How much heat is absorbed by the iron? C=450J/kg K

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