Bell workBell workJason held a basketball over his head and then

threw it toward the floor. The ball hit the floor and bounced back up into the air. Eventually, the ball stopped bouncing and rested on the floor.

When did the ball have the greatest amount of potential energy in this example?

• A. when it was high in the air, but not moving• B. when it was falling through the air towards the floor• C. when it moved back into the air after bouncing off the

floor• D. when it finally rested motionless on the floor

Energy Conservation Energy Conservation NotesNotes

ObjectivesObjectives

• Explain how energy is conserved within a closed system.

• Explain the law of conservation of energy.

• Give examples of how thermal energy is always a result of energy conversion.

• Explain why perpetual motion is impossible.

QuestionQuestion

• What do you think Energy Conservation is?

Conservation of EnergyConservation of Energy

• Energy is conserved in all cases.

• Law of conservation of energy- energy cannot be created or destroyed.

• All of the different forms of energy in a system always add up to the same total amount of energy.– It doesn’t matter how many energy

conversions take place.

Closed SystemClosed System

• A closed system is a group of objects that transfer energy only to each other.

• The total amount of energy in a closed system is always the same.

Conversion to ThermalConversion to Thermal

• Some energy is always converted to thermal energy due to friction.

– Friction is a force that opposes motion between 2 surfaces that are touching.

• The thermal energy due to friction that results from energy conversions isn’t useful energy.

– Thermal energy is not used to do work.

Where Does the Energy Go?

• For a roller coaster car to move, energy must be used to overcome the friction between the car’s wheels and the track.

• As a result, not all of the car’s potential energy changes into kinetic energy and not all of the car’s kinetic energy changes back into potential energy.

ObjectivesObjectives

• Explain how energy is conserved within a closed system.

• Explain the law of conservation of energy.

• Give examples of how thermal energy is always a result of energy conversion.

• Explain why perpetual motion is impossible.

QuestionQuestion

• Can a machine be built that would work forever without adding any more energy?

No Conversion Without Thermal Energy, continued

• Perpetual Motion? No Way! A perpetual motion machine is a machine that would run forever without any additional energy.

• But perpetual motion machines are impossible because some waste thermal energy always results from energy conversions.

No Conversion Without Thermal Energy, continued

• Making Conversions Efficient Some systems transform energy with less loss of heat than others do. Such systems are more efficient than others are.

• Improving the efficiency of machines is important because greater efficiency results in less waste. If less energy is wasted, less energy is needed to operate a machine.

Efficient Energy ConversionsEfficient Energy Conversions

• Energy efficiency- a comparison of the amount of energy before a conversion with the amount of useful energy after a conversion.

• Energy conversions that are more efficient end up wasting less energy.– Fuel efficient cars, energy efficient light bulbs.

Efficient Energy ConversionsEfficient Energy Conversions

• Improving the efficiency of machines, such as cars, is important because greater efficiency results in less waste.

• If less energy is wasted, less energy is needed to operate a machine.

QuestionQuestion

• What are some ways the we can make these conversions more efficient?

ObjectivesObjectives

• Explain how energy is conserved within a closed system.

• Explain the law of conservation of energy.

• Give examples of how thermal energy is always a result of energy conversion.

• Explain why perpetual motion is impossible.