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Thermal Energy

A.  Moving Thermal Energy
1.  Conduction
a.  The transfer of energy through matter by direct contact.
b.  Takes place in solids, liquids, and gases.
2.  Convection
a.  The transfer of energy by the movement of matter.
b.  The matter must move from one place to another.
c.  Only fluids can flow freely (liquids or gases).
3.  Radiation
a.  The transfer of energy in the form of waves.
b.  Matter is not needed for radiation.
4.  Insulators
a.  Insulators do not allow heat to move easily through them.
b.  They are assigned R values (resistance to heat flow).
c.  Examples:
1)  Gases are good insulators.
2)  Foam makes use of air pockets containing gases.
3)  Fluffy materials contain air pockets.
4)  Shiny foil reflects radiant energy.
5)  Double-pane glass windows.
B.  Heating Systems
1.  Conventional heating systems
a.  Fire
b.  Radiators
1)  Can be heated by electricity
2)  Hot water heating system
3)  Steam heating system
4)  Forced air heating system
5)  Radiant electric heating system
2.  Solar heating
a.  Passive
b.  Active - use mechanical devices to transfer heat.
C.  Using Heat to Do Work
1.  Heat engines
a.  Devices that convert thermal energy into mechanical energy by combustion (burning fuel).
b.  Internal combustion engine
1)  Fuel burns inside cylinders in the engine.
2)  Each cylinder has a piston inside that moves up and down.
3)  On each end of the cylinder is a valve.
4)  Pistons move and turn a crankshaft.
5)  The crankshaft turns and causes the axles and wheels to turn.
6)  The four stroke cycle:
a)  Intake stroke - intake valve opens and draws in a fuel-air mixture.
b)  Compression stroke - intake valve closes and the piston moves up, compressing the fuel-air mixture.
c)  Power stroke - a spark plug ignites the fuel-air mixture which forces the piston down.
d)  Exhaust stroke - the piston moves up and the exhaust valve opens to let out the waste from the burning.
7)  Diesel engines do not use spark plugs; the fuel-air mixture compresses and ignites on its own.
8)  Efficiency:
a)  Gasoline engine are about 12% efficient.
b)  Diesel engines are about 25% efficient.
c.  External combustion engines
1)  Fuel burns outside the engine.
2)  Steam engines
a)  Old fashioned ones boiled water into steam which moved pistons.
b)  New ones use steam to turn turbine blades.
2.  Heat movers
a.  Devices that remove thermal energy from one location and transfer it to another location at a different temperature (refrigerators).
b.  Heat pumps can move heat outside during warm weather and inside during cool weather.

South Carolina Physical Science standards met in this unit:

B. Conservation of Energy and the Increase in Disorder
4.  Everything tends to become less organized and less orderly over time. Thus, in all energy transfers, the overall effect is that the energy is spread out uniformly. Examples are the transfer of energy from hotter to cooler objects by conduction, radiation, or convection and the warming of our surroundings when we burn fuels.

_______a.  Understand the transfer of energy from hotter to cooler objects by conduction, radiation, and convection.