1. Objectives: (ACOS 8)
Distinguish between kinetic and potential energy.
Apply the law of conservation of energy to familiar situations.
Identify the relationship between thermal energy and the temperature of a sample of matter.
Explain how thermal energy is transferred by radiation, conduction, and convection.
Describe the flow of thermal energy.

2. Section 1: The Nature of Energy
Energy is the ability to cause change.
There are many different forms of energy:
chemical
thermal
kinetic
potential
electrical
Read “An Energy Analogy” on page 101.

3. Potential and Kinetic Energy

4. Kinetic Energy energy in the form of motion
KE = ½ mass x velocity2 KE = ½ m x v2
SI unit—Joule (J)
After 2nd bullet—The more mass a moving object has, the more kinetic energy it has. Also, the greater an object’s velocity is, the more kinetic energy it has. (Figure 3 page 102)
After 3rd bullet—It is named after the 19th century British scientist James Prescott Joule.

5. Potential Energy stored energy due to position
types of potential energy
elastic: energy stored by something that can stretch or compress (ex. rubber band, spring)
chemical: energy stored in chemical bonds (ex. gasoline, food)
gravitational: energy stored by objects that are above Earth’s surface (ex. apple or leaf in tree)
Before 1st bullet—Read the first paragraph on page 103.

6. Gravitational Potential Energy (GPE)
GPE = mass x 9.8 m/s2 x height
SI unit—Joule (J)
Bjorn is holding a tennis ball outside a 2nd story window (3.5 m from the ground) and Billie Jean is holding one outside a 3rd story window (6.25 m from the ground). How much more GPE does Billie Jean’s tennis ball have? (Each tennis ball has a mass of 0.06 kg).
Read 1st paragraph on page 104.
Bjorn: kg x 9.8 m/s2 x 3.5 m = 2.06 J
Billie Jean: kg x 9.8 m/s2 x 6.25 m = 3.68 J
Difference = 3.68 J – 2.06 J = 1.62 J more energy than Bjorn’s
Read 1st paragraph on page 105.
Go over CH 4-1 Notes Handout.

7. Section 2: Conservation of Energy
Energy is most noticeable as it transforms from one form to another.
mechanical energy = total energy (kinetic + potential)
Read 1st paragraph on page 107.
Look at Figure 7 on page 108.
Bonus: How do your kinetic and potential energy relative to an elevator change as you go up?

8. Energy Conversion

9. Law of Conservation of Energy
Energy cannot be created or destroyed.
The total amount of energy in the universe remains constant.
Read the 1st paragraph under Law of Conservation of Energy on page 111.
Read last paragraph on page 111.
Read “Following Energy’s Trail” on page 112.

10. Work (Chapter 5-1)
Work is the transfer of energy that occurs when a force makes an object move.
Two conditions must be met for work to be done on an object:
the object has to move
the movement must be in the direction of the force
Read 1st paragraph on page 126.
Look at Figures 1 and 2 on pages Read the captions. After Figure 2, read the 1st paragraph on page 127.

11. Work and Energy When work is done, a transfer of energy always occurs.
Read the last paragraph on page 127.

12. Calculating Work Work = force x distance W = F x d SI unit: Joules (J)
One joule is about the amount of work required to lift a baseball a vertical distance of 0.7m.

13. Example Problems
You move a 75 kg refrigerator 35 m. This requires a force of 90 N. How much work was done while moving the refrigerator?
3150 J
When you and a friend move a 45 kg couch to another room, you exert a force of 75 N over 5 m. How much work did you do?
375 J
See page 128.

14. Bonus
Suppose you used a force of 50 N to shoot an arrow, and the arrow flew 25 meters. As you shot the arrow, the bow string moved the arrow 1 m. Did you do 1250 J of work or 50 J of work? Explain.
You did 50 J of work, because after the arrow left the bow, it was flying loose in the air and was not experiencing any force from you.
Read 1st paragraph on page 129.

15. Power
Power is the amount of work done in a certain amount of time (the rate at which work is done).
Power = work / time P = W / t
SI unit: watts
Example: How much power is required to push a car for 10 s if the amount of work done during that time is 5,500 J?
550 W
Read 1st paragraph under Power on page 129.
After 3rd bullet—named for James Watts, who helped develop the steam engine in the 18th century
A watt is fairly small—about equal to the power needed to raise a glass of water form a table to your mouth in 1s.
Because the watt is so small, large amounts of power are measured in kW. If you were to run up a flight of steps in about 1.5 s, it would take about 1kW of power.

16. Temperature and Heat (Chapter 6)
All matter is made up of tiny particles in constant motion, meaning that they have kinetic energy.
temperature: average kinetic energy of the particles

17. thermal energy: total energy of all the molecules in an object
A larger mass has more thermal energy than a smaller mass at the same temperature, because there are more particles in the larger mass.
When the temperature of an object increases, the average kinetic energy of the molecules increase, so the thermal energy increases.

18. Heat
heat: energy that is transferred from an object at a high temperature to one at a lower temperature
Heat and work are similar. Both are energy being transferred. Both are measured in joules.
calorimeter: instrument used to measure changes in thermal energy
Suppose your hands are cold. You put them against your warm cheek. Your hands become warmer. At the same time, your cheeks become colder, their temperature decreases. Energy flows from your warm cheeks to your cold hands.
After 1st: Another way to warm your hands is to rub them together. Energy is changed from kinetic energy of your moving hands into thermal energy. Remember that energy that is transferred at the result of motion is work.

19. Transferring Thermal Energy

20. Conduction
conduction: transfer of energy through matter by the direct contact of particles
Conduction occurs because of the collisions between particles.
insulators: material that doesn’t allow heat to flow through it easily
Examples: snow in handsnow melts, hand becomes colder
hot chocolatehand becomes warm, cup cools off
Why do solids conduct heat better than liquids or gases?
The particles are closer together so they collide more often.
Good conductors are poor insulators.

21. Convection fluid: anything that flows (liquids, gases)
convection: transfer of energy in a fluid by the movement of the heated particles
Convection currents are rising-and-sinking actions that transfer heat from warmer to cooler parts of a fluid.
In convection, more energetic particles move from one location to another carrying their energy with them.

22. Radiation radiation: transfer of energy by electromagnetic waves
Electromagnetic waves can travel through space even when no matter is present.
When radiation strikes a material, some of the energy is absorbed, some is reflected and some may be transmitted through the material.
Light colored materials reflect more radiant energy.
Dark colored materials absorb more radiant energy.