DAILY QUESTION

February 18, 2009

1. What two energy sources are often used for heating systems?

Agenda 2/18/09

• Daily Question• Ch 13 Section 3 Notes• Assignments:

1. 13-2/3 Worksheet due 2/19

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

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

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

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

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

Heating Systems

• In general, the amount of usable energy always decreases whenever energy is transferred or transformed– Insulation can minimize undesirable energy

transfers

Cooling Systems

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

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

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