ENGINES AND REFRIGERATORS
8TH GRADE
CHAPTER 21 SECTION 3
DO NOW…
•In order to heat a room evenly, should
heating vents be placed near the floor or
near the ceiling? Explain.
OBJECTIVES
• Students will…
• Describe what a heat engine does.
• Explain that energy can exist in different forms, but is never created or
destroyed.
• Describe how an internal combustion engine works.
• Explain how refrigerators move thermal energy.
HEAT ABSORPTION
• Specific Heat- is the amount of thermal energy needed to
raise the temperature of 1kg of the substance by 1
degree C.
• More thermal energy is needed to change the temperature
of a material with a high specific heat than one with a low
specific heat.
• Ex: sand on a beach has lower specific heat than ocean
water
THERMAL POLLUTION
• Thermal pollution- increase in the temperature of a body of water
caused by adding warmer water.
• Effects: organisms need more oxygen and warmer water has less
dissolved oxygen=organisms die due to low oxygen. Also
organisms are more sensitive to chemical pollutants, parasites and
disease.
• Reducing: Cooling warm water produced by factories, power plants
and run off.
HEAT ENGINES-DEVICES THAT CONVERT THERMAL
ENERGY INTO MECHANICAL ENERGY.
Types of Energy
Chemical Energy—burning
fuel
Radiant Energy—heat from a
fire
Nuclear Energy– splitting
atoms in a power plant
Electrical Energy-lightning
Thermal Energy-energy in a
hot cup of tea
Mechanical energy-Moving
Train
THE LAW OF CONSERVATION OF ENERGY
• When energy is transformed from one form to another, the
total amount of energy doesn’t change.
• Energy cannot be created or destroyed.
• Energy only can be transformed from one form to another.
• No device (even a heat engine) can produce or destroy
energy.
INTERNAL COMBUSTION ENGINE
• A heat engine in which fuel burns in a combustion chamber inside
the engine.
• Examples: cars, airplanes, buses, boats, trucks and lawn mowers.
• Most modern cars are powered by fuel-injected internal combustion
engines that have a 4 stroke combustion cycle.
• Inside the engine, thermal energy is converted into mechanical
energy as gas is burned under pressure inside the chambers known
as cylinders.
STEPS IN THE FOUR-STROKE CYCLE (FOLDABLE)
• 1) Intake Stroke
• - The piston moves downward.
• -Air fills the cylinder through the intake valve.
• -A mist of fuel is injected into the cylinder.
• 2) Compression Stroke
• -The piston moves upward, compressing the fuel-air mixture.
STEPS IN THE FOUR-STROKE CYCLE
• 3) Power Stroke
• -A spark from the spark plug ignites the fuel-air mixture.
• - The hot gases expand, pushing the piston down and turning
the crankshaft.
• 4) Exhaust Stroke
• - The exhaust valve opens as the piston moves up. Exhaust gases
are forced out of the cylinder.
VIDEOS
• Heat as Energy (eureka)
• 4 Stroke Cycle
FOR NEXT TIME…
•Read pgs. 619-623
•Define work, heat engine, and internal combustion
engine.
ENGINES AND REFRIGERATORS
8TH GRADE
CHAPTER 21 SECTION 3
DO NOW…
•Name the steps in the 4 stroke cycle.
•Heat as Energy (eureka
OBJECTIVES
•Students will…
•Explain how refrigerators move thermal energy.
REFRIGERATORS (GIVE OUT WORKSHEET)
• A refrigerator is a heat mover.
• It absorbs thermal energy from the food inside the fridge and then it carries
the thermal energy to outside the refrigerator where it is transferred to the
surrounding air.
• A refrigerator contains a material called a coolant that is pumped through
the pipes inside and outside the fridge.
• The coolant is the substance that carries thermal energy from the inside to
the outside of the refrigerator.
AIR CONDITIONERS AND HEAT PUMPS
• AC units cool in a similar manner to refrigerators.
• Thermal energy from inside the house is absorbed by the coolant
within the pipes inside the air conditioner.
• The coolant becomes compressed by a compressor and becomes
warmer.
• Then the warmed coolant travels through pipes that are exposed to
the outside air.
HEAT PUMPS (HEATING/COOLING)
• A heat pump moves thermal energy from one place to another.
• Heating mode: coolant absorbs thermal energy through outside
coils. The coolant is warmed when it is compressed and transfers
thermal energy to the house through the inside coils.
• Cooling mode: It removes thermal energy from the indoor air and
transfers it outdoors.
BILL NYE: ENERGY
• Bill Nye Energy
FOR NEXT TIME…
• Read pg. 626
• Answer: What factors need to be considered when
planning expansion of cities?
REVIEWING THERMAL ENERGY
8TH GRADE
DO NOW…
• What factors need to be considered when planning
expansion of cities?
• Review homework
OBJECTIVES
•Students will…
•Begin to review chapter 21 thermal heat
CHAPTER 21 REVIEW PACKET
• Begin working on review packet for Chapter 21.
• Review packet (all 3 pages) needs to be completed by
Tuesday.
• Reminder guest speakers on Monday.