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UNIT 2: Physics
Chapter 5: Energy (pages 126-151)
I. The Nature of Energy
A. What is energy?
1. Energy- defined as the
ability to do work, or the
ability to cause change
2. Work- is done when a force causes something to
move
If you push really hard on
something but it does not move,
have you done work on it?
3. Energy comes in several
forms (electrical, chemical,
radiant, and thermal)
B. Kinetic Energy- energy of a moving object
1. Equation:
1 2
KE  mv
2
2.SI unit is a joule
3. Kinetic energy depends on objects mass
and velocity
C. Potential Energy- stored energy
1. Potential energy- stored energy due to its
position
2. Elastic potential energy- energy stored by
something that can stretch or compress such as
rubber band or spring
3. Chemical potential energy- energy stored in the
chemical bonds that hold atoms together
4. Gravitational potential energy- energy stored
due to the objects position above Earth’s surface
GPE  mgh
5. If an object falls, its GPE will decrease and
become KE
PE
PE
KE
KE
II. Conservation of Energy
A. Changing Forms of Energy- energy is
constantly being changed from one form to
another
1. Transforming
electrical energyelectrical energy can
be transformed into
light, thermal energy,
kinetic energy
2. Transforming chemical energy- engine
transforms chemical potential energy into kinetic
energy of moving car.
a. Some less obvious- plants convert light energy
into chemical potential energy (photosynthesis)
b. Animals eat food (chemical potential energy) and
convert to other forms in you body (cellular
respiration)
ENERGY
ENERGY
ENERGY
B. Conversions between kinetic and potential
energy
1. Mechanical energy of a system:
mechanical energy = potential energy + kinetic energy
100 PE + 0 KE = 100 ME
0 PE + 100 KE = 100 ME
2. As an object falls, GPE is converted into KE.
The total mechanical energy still remains the
same
3. In projectile motion, object starts with large KE,
small GPE. At the top it has lower KE and higher
GPE. Right before it hits the ground it has high KE
and low GPE
C. Law of Conservation of Energy- states that
energy cannot be created or destroyed. The
same amount always exists
1. Energy conservation- try and conserve
“non-renewable” resources like
gasoline and coal
2. Sometimes it is hard to see law of conservation
of energy at work
3. Friction and air resistance can decrease
mechanical energy of a system creating thermal
energy
4. Nuclear fusion can change a small amount of
mass into a large amount of energy (in the Sun).
Nuclei fuse together
5. Nuclear fission- converts small amount of mass
into large amounts of energy. Nuclei broken apart
D. The Human Body- Balancing the Energy
Equation
1. Processes in your body
obey law of conservation of
energy
a. Chemical potential
energy is your bodies
fuel
b. Converted into heat
and energy to make
your body move
2. Food energy- measured in Calories (C)
a. Nutrition labels on food packages tell us
how many Calories or contained
b. Chart of Calorie-Burning Activities