Presentation on theme: "Engines and refrigerators"— Presentation transcript:
1Engines and refrigerators 8th GradeChapter 21 Section 3
2Do Now…In order to heat a room evenly, should heating vents be placed near the floor or near the ceiling? Explain.
3Objectives 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.
4Heat AbsorptionSpecific 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
5Thermal PollutionThermal 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.
6Heat Engines-devices that convert thermal energy into mechanical energy. Types of EnergyChemical Energy—burning fuelElectrical Energy-lightningRadiant Energy—heat from a fireThermal Energy-energy in a hot cup of teaNuclear Energy– splitting atoms in a power plantMechanical energy-Moving Train
7The 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.
8Internal 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.
9Steps 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.
10Steps 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.
12Define work, heat engine, and internal combustion engine. For Next Time…Read pgsDefine work, heat engine, and internal combustion engine.
13Engines and Refrigerators 8th GradeChapter 21 Section 3
14Name the steps in the 4 stroke cycle. Heat as Energy (eureka Do now…Name the steps in the 4 stroke cycle.Heat as Energy (eureka
15Explain how refrigerators move thermal energy. ObjectivesStudents will…Explain how refrigerators move thermal energy.
16Refrigerators (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.
17Air 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.
18Heat 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.