• Stored Energy
• Energy of Position
• Working Energy
• Energy of Motion
1
Potential Energy becomes Kinetic Energy.
or in other words…
Stored Energy becomes Working Energy
For example…
a rubber band zinged from your finger has kinetic energy. While it
was stretched, waiting for you to release it, it had potential energy.
The rubber band was stationary (not moving), but work had been
done on it to move it to its present position.
This again is an energy transformation.
2
The formulas to calculate Potential Energy are…
Potential Energy = weight X height
PE = wh
PE is measured in Joules (J) Weight is given in
Newtons (N) & height in meters (m)
Gravitational Potential Energy =
mass X gravity’s acceleration X height
GPE = mgh
Mass is given in kilograms (kg), gravity’s
acceleration is 9.8m/s2 & height is in meters (m)
3
Problem:
A 17N flower pot is lifted to a height of 3 meters. What is
the energy of this object?
GUESS Read the problem, draw a picture and write down what is
given in the problem.
GUESS Write down the unknown variables in the problem.
Given
W = 17N
h = 3m
GUESS
Unknown
Potential
Energy
Equations Needed
PE = wh
Substitute including units
PE = 17N x 3m
Solution
PE = 51
Joules
Write down the equation needed to solve the problem.
GUESS
Substitute the known variables into the equation including the UNITS.
GUESS
Solve the equation including the UNITS.
4
Problem:
A 30 kg child climbs 15m up a tree. When she stops to
look around, what is the child’s energy?
GUESS Read the problem, draw a picture and write down what is
given in the problem.
GUESS Write down the unknown variables in the problem.
Given
M = 30kg
h = 15m
GUESS
Unknown
Equations
Needed
GPE GPE = mgh
Substitute including units
Solution
GPE = 30kg X 9.8m/s2 x 15m
PE = 4410
Joules
Write down the equation needed to solve the problem.
GUESS
Substitute the known variables into the equation including the UNITS.
GUESS
Solve the equation including the UNITS.
5
6
The formula to calculate Kinetic Energy is…
Kinetic Energy = ½ (mass x velocity2)
KE = mv2
2
Units for Kinetic Energy are – Joules (J)
Units for Mass are – kilograms (kg)
Units for Velocity are – (m/s)
7
Problem:
What is the energy of a 25kg tennis ball being hit at a
velocity of 13m/s?
GUESS Read the problem, draw a picture and write down what is
given in the problem.
GUESS Write down the unknown variables in the problem.
Given
Unknown
Equations Needed
Substitute including units
Solution
KE = 25kg (13m/s)2
M = 25kg
v = 13m/s
2
KE
KE = mv2
2
KE = 25kg (169m2/s2)
2
KE =
2112.5
Joules
KE = 4,225kg.m2/s2
2
GUESS
Write down the equation needed to solve the problem.
GUESS
Substitute the known variables into the equation including the UNITS.
GUESS
Solve the equation including the UNITS.
8
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