PART 2

Energy

Learning Goals for Section 2Conservation of Energy

Describe how energy can be transformed from one form to another.

Explain how the mechanical energy of a system is the sum of the kinetic and potential energy.

Discuss the law of conservation of energy.

Conservation of Energy

Energy Transformations, Example #1

1. Separate a few strands of steel wool from a large wad.

2. Hold the strands with tongs. Touch each end of the steel wool strand to the battery terminals of a 9-V battery.

3. Write your observations of what happens.4. Describe the energy transformations

observed.

Conservation of Energy

Energy Transformations, Example #2

1. Take a few minutes to play with the toy popper.

2. Think about the energy transformations that take place as the toy “pops” from the table.

3. Draw a diagram of what happens as the toy pops. Label the diagram with the different forms of energy observed and the energy transformations that occur.

Conservation of Energy

Energy Transformation Examples:light energy to chemical energy (Photosynthesis)

electrical energy to heat energy (happens in light bulbs)

Chemical energy to thermal energy to kinetic energy (happens in car engines)

Conversions Between Kinetic and Potential Energy

mechanical energy = PE + KEPotential Energy Kinetic EnergyRoller coaster: 1) Energy required for ride comes from work done

by the conveyor that lifts the cars and passengers.2) Energy from initial work is stored as GPE at the top of the first hill.3) Energy transformations begin: kinetic to potential to kinetic, etc., heat energy, sound energy.

One of the tallest roller coaster’s in the world is the Fujiyama, in Fujiyama Highland Park, Japan. It spans 70 m from its highest to lowest points.

Energy Transformations: Potential to Kinetic and Kinetic to Potential

PE=354kJKE= 0kJv= 0m/s

h=70.0m

m=515kg

PE= 0kJKE= 354kJv= 37.1 m/s

m=515kg

h=35.0m

KE=354 kJPE= 0 kJv=37.1 m/s

KE=177 kJPE= 177 kJv=26.2 m/s

As a car goes down a hill on a roller coaster, potential energy transforms to kinetic energy.

At the top of this small hill, half the kinetic energy has transformed into potential energy. The rest of the kinetic energy carries the car over the crest of the hill at high speed.

The Law of Conservation of Energy

Energy cannot be created or destroyed.Energy may be transformed from one form

into another.Energy may be transferred from one object to

another.The total amount of energy never changes.