Energy

1
Energy

• The ability to do work.
• An object has energy if it is able to produce
  change in itself or its surroundings.

2
Energy exists in different forms

• Mechanical energy (moving objects and their
  positions)
• Radiant energy (light and solar energy)
• Chemical energy (including the food you eat and
  fuels we burn)
• Thermal or heat energy (molecules moving faster
  means more heat)
• Electrical energy (electrons moving through a
  wire)
• Nuclear energy (energy locked in the nucleus of
  an atom)

3
Energy can be transferred

• Fossil fuels like coal and oil can be burned to
  heat water that boils into steam that turns a
  turbine to generate electricity that you use to
  operate a stereo.
• Chemical energy ? Thermal energy
• Thermal energy ? Kinetic energy
• Kinetic energy ? Electrical energy

4
Energy cannot be created or destroyed.

• In the example of riding a bicycle down a steep
  hill, you begin with a lot of potential energy at
  the top of the hill and gain kinetic energy as
  you coast down the hill.
• If you are not making the kinetic energy
  (movement down the hill), where does it come
  from? The answer is simple your potential
  energy at the top is transformed into kinetic
  energy as you speed along.

5
Mechanical Energy

• Kinetic Potential
• Kinetic is the energy of moving objects.
• Potential Energy is stored energy.
• Gravitational PE is energy due to position.

6
Potential Energy

• Energy that is a result of an objects position
  or condition.
• All potential energy is Stored Energy.
• Pull back on a bow string and bend the bow. The
  object then possesses potential energy.

7
Potential Energy

• A rock on a table top has more potential energy
  than when it is on the ground due to its
  position.
• This is a form of gravitational potential energy.

8
Gravitational Potential Energy

• Depends on mass and height.
• GPE m(g)h
• m mass
• g acceleration due to gravity
• h height
• -What are the Units of GPE? Joules

9
SI units?

• m kg
• g m/s2
• h m
• PE J

10
Question 1

• A man lifts a 2 kilogram book from the floor to
  the top of a 1.25 meter tall table. What is the
  change in the books gravitational potential
  energy?

1. 0 joules
2. 2.50 joules
3. -2.50 joules
4. 24.525 joules
5. -24.525 joules

11
Answer 6 (d) 24.525 J

• A man lifts a 2 kilogram book from the floor to
  the top of a 1.25 meter tall table. What is the
  change in the books gravitational potential
  energy?

12
Question 2

• A mouse now pushes a book (2 kg) off the table
  (1.25m). What is the change in the books
  gravitational potential energy?

1. 0 joules
2. 2.50 joules
3. -2.50 joules
4. 24.525 joules
5. -24.525 joules

13
Answer 7 (e) -24.525 J

• A man lifts a 2 kilogram book from the floor to
  the top of a 1.25 meter tall table. What is the
  change in the books gravitational potential
  energy?

14
Kinetic Energy

• Energy that appears in the form of motion.
• Depends on the mass and speed of the object in
  motion.

15
Kinetic Energy

• KE (1/2)mv2
• m mass v velocity
• Unit for energy is Joule (J)

16
Kinetic Energy

• Energy due to motion.
• A brick falling at the same speed as a ping pong
  ball will do more damage.
• KE is dependent on mass.
• KE also depends on speed (v)

17
Which would affect the kinetic energy of an
object more, doubling its mass or its velocity?
Kinetic Energy

• doubling the mass would result in a doubling of
  the KE.
• doubling the velocity would quadruple the KE.

18
Question 8

• What is the KE of a 1140 kg (2513 lb) car driving
  at 8.95 m/s (20 mph)?

1. 0 joules
2. 5101.5 joules
3. 10203 joules
4. 4.57x104 joules
5. Im lost

19
Answer 8 (d) 45658.4 J

• What is the KE of a 1140 kg (2513 lb) car driving
  at 8.95 m/s (20 mph)?

20
Recall, Law of Conservation of Energy

• Energy can not be created nor destroyed.
• Energy can change from one form to another.
• The total energy in the universe is constant.

21
Conservation of Energy

• In a roller coaster all of the energy for the
  entire ride comes from the conveyor belt that
  takes the cars up the first hill.