1. ENERGY
Sabar Nurohman,M.Pd

2. Energy as a tool in physics
The Flow of Energy
4/11/2005
Energy is a very abstract notion, but it is a very useful and quantifiable notion
We use the conservation of energy to predict behavior
by setting E = mgh + ½mv2 = constant we can elucidate the value of the velocity at any height:
v2 = 2g(height fallen from rest)
We rely on the fact that energy is not created out of nowhere
Where did the energy we see around us come from?
most of what we use derives from the sun
some derives from other, exploded stars (nuclear fission)
ultimately, all of it was donated in the Big Bang
but surprisingly, the net energy of the universe can be (and looks to be) zero!
Lecture 4

3. Energy is Conserved
The Flow of Energy
4/11/2005
Conservation of Energy is different from Energy Conservation, the latter being about using energy wisely
Conservation of Energy means energy is neither created nor destroyed. The total amount of energy in the Universe is constant!!
Don’t we create energy at a power plant?
No, we simply transform energy at our power plants
Doesn’t the sun create energy?
Nope—it exchanges mass for energy
Lecture 4

4. The Flow of Energy
Energy Exchange
4/11/2005
Though the total energy of a system is constant, the form of the energy can change
A simple example is that of a pendulum, in which a continual exchange goes on between kinetic and potential energy
pivot
K.E. = 0; P. E. = mgh
K.E. = 0; P. E. = mgh
height reference h
P.E. = 0; K.E. = mgh
Lecture 4

5. Perpetual Motion Why won’t the pendulum swing forever?
The Flow of Energy
4/11/2005
Why won’t the pendulum swing forever?
It’s impossible to design a system free of energy paths
The pendulum slows down by several mechanisms
Friction at the contact point: requires force to oppose; force acts through distance  work is done
Air resistance: must push through air with a force (through a distance)  work is done
Gets some air swirling: puts kinetic energy into air (not really fair to separate these last two)
Perpetual motion means no loss of energy
Lecture 4

6. Mechanical, Electromagnetic, Electrical,
TYPES OF ENERGY
Mechanical, Electromagnetic, Electrical,
Chemical and Thermal

7. What is Mechanical Energy?
Energy due to a object’s motion (kinetic) or position (potential).
The bowling ball has mechanical energy.
When the ball strikes the pins, mechanical energy is transferred to the pins!

8. Examples of Mechanical Energy

9. What is Electromagnetic Energy?
Light energy
Includes energy from gamma rays, xrays, ultraviolet rays, visible light, infrared rays, microwave and radio bands

10. What is Electrical Energy?
Energy caused by the movement of electrons
Easily transported through power lines and converted into other forms of energy

11. What is Chemical Energy?
Energy that is available for release from chemical reactions.
The chemical bonds in a matchstick store energy that is transformed into thermal energy when the match is struck.

12. Examples of Chemical Energy

13. What is Thermal Energy?
Heat energy
The heat energy of an object determines how active its atoms are.
A hot object is one whose atoms and molecules are excited and show rapid movement.
A cooler object's molecules and atoms will show less movement.

14. ELECTROMAGNETIC ENERGY
QUIZ TIME!
What type of energy cooks food in a microwave oven?
ELECTROMAGNETIC ENERGY
What type of energy is the spinning plate inside of a microwave oven?
MECHANICAL ENERGY

15. QUIZ TIME!
Electrical energy is transported to your house through power lines.
When you plug an electric fan to a power outlet, electrical energy is transform into what type of energy?
MECHANICAL ENERGY

16. QUIZ TIME!
What energy transformation occurs when an electric lamp is turned on?
ELECTRICAL ENERGY 
ELECTROMAGNETIC ENERGY

17. What types of energy are shown below?
Mechanical and Thermal Energy
(Don’t forget friction)

18. What type of energy is shown below?
Chemical Energy

19. What types of energy are shown below?
Electrical, Mechanical and
Electromagnetic Energy

20. What type of energy is shown below?
Chemical Energy (yummy)

21. What type of energy is shown below?
Thermal Energy

22. Draw a flow map showing the flow of energy transformations in a car from starting vehicle to driving. You should have 5 different types of energy.

23. Energy Transfer Sound (mechanical) Electrical Thermal Mechanical
Chemical
Electrical
Light
(Electromagnetic)