Download Energy Conservation Notes

Bell work
Jason 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
Notes
Objectives
• 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.
Question
• What do you think Energy Conservation
is?
Conservation 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 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 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.
Objectives
• 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.
Question
• 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 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 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.
Question
• What are some ways the we can make
these conversions more efficient?
Objectives
• 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.