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Practical Heat Energy Calculations for Physics Enthusiasts

Explore heat energy calculations in physics, including rotational kinetic energy, heat gained during heating processes, energy transfers, and changes of state. Learn about conduction, convection, radiation, sensible and latent heat energy.

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Practical Heat Energy Calculations for Physics Enthusiasts

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  1. PT Unit Five Subunit four

  2. 1 calorie = 4.184 J or 3.086 ft x lb • 1 kilocalorie = 4184 J or 3086 ft x lb • 1 Btu = 778 ft x lb or 1054 J

  3. A 180 kg reel of wire rotates at 350 rpm (about 37 rad/sec). The effective radius of the reel (sh • aped like a cylinder) 0.41 m. The rotating reel is brought to a stop by a mechanical friction brake with a drum and brake lining. • Find a. Rotational kinetic energy of reel. • B. Heat energy equivalent of rotational kinetic energy.

  4. B. Assume all the kinetic energy goes into heat energy developed during the stopping action of the brake. • Total heat energy developed = • 10.356 J X 1kcal/4184J = 2.475 kcal

  5. Subunit four • Calculate the heat gained by a 15 Kg mass of copper when it is heated from 10°C to 125°C

  6. Subunit four • Calculate the heat gained by a 15 Kg mass of copper when it is heated from 10° • C to 125 °C. • H = mcT • H = 15 kg (.093 kcal/(kg ● °C)) (115 °C) • H = 160.42 kcal

  7. Heat Gained = Heat lost • Heat = mc∆t • Heat = Heat energy transferred • M = Mass • c = specific heat • ∆t = temperature

  8. To harden a steel sledgehammer, a manufacturer heats the 4.5 kg hammer to 650 °C and quenches it in an insulated oil container. The hammer cools to 250 °C. Oil temperature increases from 200 °C to 250 °C. The specific heat of steel is: • c= 0.11 kcal/kg C° • Find amount of heat energy removed from the hammer and added to the oil bath. • Find the specific heat of the oil bath if the mass of the oil is 70 kg.

  9. Three ways to transfer energy • 1. Conduction • 2. Convection • 3. Radiation

  10. Conduction is the transfer of thermal energy from a hot region to a cold region by direct transfer of molecular virbation from molecule to molecule.

  11. Convection is the transfer of thermal energy by movement of a fluid medium from one region to another

  12. Radiation is the transfer of heat energy by motion of electromagnetic radiation. (NO medium required)

  13. Changes of State • Melting = Change from solid to liquid • Freezing = Change from liquid to solid • vaporization = change from liquid to gas • Condensation = change from gas to liquid • Sublimation = change from solid to gas

  14. Sensible heat energy involved when a substance gains energy producing a temperature change. Change in kinetic energy. • Latent heat energy involved when substance undergoes a change of state. • There is no temperature change. Means hidden energy. Change in potential energy.

  15. Latent heat of Fusion: Heat required to melt a gram (kilogram) of a substance. • Latent heat of vaporization: Heat required vaporize a gram (kilogram) of a substance.

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