# Note 2 - Topic 2 Thermal Energy and Heat Thermal Energy and Power Transforming Energy Energy in Humans Temperature Heat Heat Transfer Home Heating

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1 1 Topic 2: Thermal Energy and Heat • Thermal Energy and Power • Transforming Energy • Energy in Humans • Temperature • Heat • Heat Transfer • Home Heating Penguins in a huddle during a snow-storm Penguin Huddle 2 Thermal Energy and Power ; Transforming Energy; Energy in Humans; Temperature; Heat; Heat Transfer; Home Heating 3 Thermal Energy and Power ; Transforming Energy; Energy in Humans; Temperature; Heat; Heat Transfer; Home Heating • Atoms are bound in a solid but they vibrate near their equilibrium position. • Molecules in a liquid only weakly bound. Thermal energy in a liquid is mostly in (linear) motion of molecules but also in vibrations and rotations of molecules. • Thermal energy in gas is mostly equal to the total kinetic energy of the atoms or molecules

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2 4 Thermal Energy and Power ; Transforming Energy; Energy in Humans; Temperature; Heat; Heat Transfer; Home Heating • Power = Energy flow per unit time Unit: 1 watt. 1W = 1J/s • Energy unit used by power companies: 1kWh 1 kilowatt = 1000J/s so 1000J = 1kWs How much energy (in J) is 1 kilowatt-hour? • 1 Calorie (food) = 1000 calories = 4200 J (1 Cal = 1kcal = 4.2 kJ) t E P Δ Δ = 5 i>Clicker Question A kWh in B.C. costs currently ~ 6.5 cents. The total energy consumption in a 1000 ft 2 large apartment is approximately 200 MJ/day. If the apartment is heated electrically, what’s the energy cost each day? A. \$ 11 B. \$ 3.60 C. \$ 2.30 D. 71 c E. 48 c 6 Thermal Energy and Power ; Transforming Energy; Energy in Humans; Temperature; Heat; Heat Transfer; Home Heating • Power: Rate of Energy Transfer Computer: ~ 200 W TV on standby: a few W Electrical stove: 3 – 5 kW Refrigerator: 1.2 kWh/day (What is this in watts?) (50 W)
3 7 Thermal Energy and Power; Transforming Energy ; Energy in Humans; Temperature; Heat; Heat Transfer; Home Heating • Energy can be transformed from one form to another (e.g., potential into kinetic). • In addition not all of the available energy can be transformed: Wind or water going through a turbine must still have some speed going out. • These limitations are expressed as efficiency . It describes how much of the available energy can be transformed into a useful form: e = useful/available . 8 A car engine has typically an efficiency of 20%. How much gasoline is used just to accelerate a 1500 kg car from rest to a speed of 15 m/s? The available chemical energy from gasoline is 34.6 MJ per liter (Wikipedia). A. 0.010L B. 0.024L C. 0.17L D. 0.84L E. 1.42L i>Clicker Question 9 Thermal Energy and Power; Transforming Energy ; Energy in Humans; Temperature; Heat; Heat Transfer; Home Heating • Kinetic energy of a solid object can be transformed into thermal energy or heat. • Example: Book sliding on a table top. While the book

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## This note was uploaded on 11/03/2009 for the course PHYSICS PHYS 100 taught by Professor Lioudmila during the Spring '09 term at The University of British Columbia.

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Note 2 - Topic 2 Thermal Energy and Heat Thermal Energy and Power Transforming Energy Energy in Humans Temperature Heat Heat Transfer Home Heating

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