Energy
Kinetic and Potential
What is Energy?
The ability to do work.
Work = Force X Distance
Forms of Energy:
Electrical
Mechanical
Thermal
Radiant
Gravitational
Nuclear
The total amount of energy in a closed system is
conserved. That is to say that energy can not be created
nor destroyed, but can transform from one type of energy
into another.
Examples:
rock falling down a hillside
solar energy changing to electrical energy
chemical energy changing to radiant energy
nuclear energy changing to thermal energy
Energy is measured in
Joules!
Potential Energy
= Mass X Gravity X Height
Kinetic Energy
Energy given to an object due to
its position above the earth’s
surface.
= ½ mass X Velocity2
Gravitational Potential Energy
= Mass ( Kg) X Gravity (9.8 m/s/s) X Height ( M )
How much potential energy would a 3 Kg rock have if it is
placed on a hill that is 20 meters tall?
M = 3 Kg
G = 9.8 m/s/s
H = 20 meters
PE = 3 Kg X 9.8m/s/s x 20 m
= 588 Joules = .588 Kjoules
Kinetic Energy =
½ Mass ( Kg) X Velocity2 (m/sec)
A 30 Kg athlete is running with a velocity of 18 m/sec
toward the finish line, what is her kinetic energy?
M = 30 Kg
KE = ½ 30 Kg x (18 m/sec)2
KE = 4860 Joules
V = 18 m/sec
Conservation of Potential
Energy

Since energy can
not be created nor
destroyed, an object
with gravitational
potential energy will
transform that
energy into kinetic
energy as it
descends.
Pendulum, device consisting of an object
suspended from a fixed point that swings back and
forth under the influence of gravity
High
Potential
High
Potential
Zero
Kinetic
Zero
Kinetic
High Kinetic
Zero Potential
20 M
15M
A high diver in the circus, or a platform
diver in the Olympics are great examples
of the Law of Conservation of Energy.
Imagine a 60 Kg diver at the top of a
platform that is 20 meters above the
pool. What are the potential and kinetic
energies at 20 m, 15m, 10 m and 2 m
above the pool?
10M
2M
A 30 Kg rock is dropped from a 30 meter tall cliff.
Complete the following table
Height above
the ground (m)
Potential
Kinetic Energy
Energy (Joules) (Joules)
30
4,312
0
High jumpers are also great examples
of the law of conservation of energy.
The jumper starts with zero potential
energy on the ground, but creates
great kinetic energy by running
toward the high jump bar.
KEi + PEi = KEf + PEf
The jumper then creates vertical
lift and changes their kinetic
energy into potential energy as
she rises toward the peak of her
jump.
Neglecting air resistance, a high jumper could use
their top sprinting speed to determine how high
they could jump.
If a 60 Kg athlete can run 8 m/sec, how high could
they possibly jump off of the ground?
M = 60 Kg
V = 8 m/sec
PEi = 0 Joules
KEf = 0 joules
So:
KEi = Pef
2
½ (60Kg) X (8m/sec) = 60Kg x 9.8 m/s/s x H
2
H = ½ (60 Kg) X (8 m/sec) / 60 Kg x 9.8 m/s/s = 3.3 m
Therefore:
Pole Vaulting
Also an example of the law of
conservation of energy
 The pole is used as a means to transfer
energy from the athlete, to the pole
and finally back to the athlete
 The composition of the pole gives
definite advantage to the athlete

Potential
Potential
stored
Kinetic
kinetic
http://www.polevaultpower.com/me
dia/video/
http://www.neovault.com/
Use your knowledge of Newton’s
laws of motion, gravitational force,
centripetal force and acceleration,
kinetic and potential energies.
Roller coasters and many
other amusement park rides
are excellent examples of
physics principles. In a 5
paragraph, typed essay
describe the physics involved
with a specific amusement
park ride of your choice. Be
sure to underline specific
physics terms and references
to physics principles or laws
within your writing. Double
space and use size 12 font. A
full page labeled diagram
should be included.