ENGINES AND REFRIGERATORS8TH GRADECHAPTER 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

Electrical Energy-lightning

Radiant Energy—heat from a fire

Thermal Energy-energy in a hot cup of tea

Nuclear Energy– splitting atoms in a power plant

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 REFRIGERATORS8TH GRADECHAPTER 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 ENERGY8TH 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.