1. DAILY QUESTION February 18, 2009 1. What two energy sources are often used for heating systems?

2. Agenda2/18/09 Daily Question Ch 13 Section 3 Notes Assignments: 1. 13-2/3 Worksheet due 2/19

3. Using Heat Two Main principles –First law of thermodynamics: Total energy in conserved. (Law of conservation of energy) –Energy that is transferred as heat always moves from an object at a higher temperature to an object at a lower temperature

4. Heating Systems Work can increase average kinetic energy –Mechanical processes: processes that involve energy transfer by work Rubbing hands together Stick and stone method of lighting a fire

5. Heating Systems Some of the energy from food is transferred as heat to blood moving throughout the human body –Skin transfers heat to cool air –Nutrients break down to warm blood –Blood warms skin

6. Heating Systems Heated water or air transfers energy as heat in central heating systems –Building transfers heat to cool air –Energy from furnace warms water, steam, or air –Pipes warm the building

7. Heating Systems Solar heating systems also use warmed air or water –Building transfers heat to cool air –Solar collector gathers energy –Energy is used to heat water or air –Hot water or air is moved through house warming it up

8. Heating Systems In general, the amount of usable energy always decreases whenever energy is transferred or transformed –Insulation can minimize undesirable energy transfers

9. Cooling Systems Energy is transferred as heat from one substance to another, leaving the first substance with less energy and thus a lower temperature

10. Cooling Systems Refrigerator: –Uses evaporation of a refrigerant to transfer energy from their surroundings Heat pumps: –A refrigeration unit in which the cooling cycle can be reversed Cools in the summer and heats in the winter

11. Heat Engines Convert potential chemical energy and internal kinetic energy to mechanical energy by using the process of combustion –Internal combustion engines (burn fuel inside the engine) Car and truck engines –External combustion engines Steam engines