LAW OF CONSERVATION OF ENERGY
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#1: What caused the penny to go up into the
air?
 What did you have to do to make sure it went
almost up to the ceiling without hitting it?
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#3-5: What happened to the deflection as the
ball was rolled from a higher distance?
#6-9: What happened as you increased the
deflection of the ruler from 2 cm to 6 cm?
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A force can change the position and speed of
an object in a way that allows the position
and speed to change back to how it was
originally
What allows for this?
Law of Conservation of Energy – energy cannot be
created or destroyed; it can be transformed from one
form to another, but the total amount of energy
remains constant
Kinetic Energy – energy associated with motion; KE =
½ mv2
Potential Energy – energy associated with position
Gravitational Potential Energy – the energy an object
possesses because of its vertical position from Earth;
GPE = mgh
Elastic Potential Energy – the energy of a spring due to
its compression or stretch; EPE = ½ kx2
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In Case You Missed it: ENERGY CANNOT BE
CREATED OR DESTROYED! IT IS
TRANSFORMED FROM ONE FORM TO
ANOTHER!
Total Energy = Kinetic Energy + Potential
Energy
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Review: What must happen in order for an
acceleration to occur?
Work – the product of the displacement and the force in
the direction of the displacement; W=Fd
Law of Conservation of Energy – energy cannot be created or
destroyed; it can be transformed from one form to another, but
the total amount of energy remains constant
Kinetic Energy – energy associated with motion; KE = ½ mv2
Potential Energy – energy associated with position
Gravitational Potential Energy – the energy an object possesses
because of its vertical position from Earth; GPE = mgh
Elastic Potential Energy – the energy of a spring due to its
compression or stretch; EPE = ½ kx2
Work: W=Fd; W = Work (N•m), F = Force (N), d =
distance (m)
Elastic Potential Energy: EPE = ½kx2; EPE = Elastic
Potential Energy (N•m), k = spring constant (N/m), x =
amount of bending (m)
Gravitational Potential Energy: GPE = mgh; GPE =
Gravitational Potential Energy (N•m), m = mass (kg), g
= acceleration due to gravity (m/s2), h = height
through which object is lifted (m)
Kinetic Energy: KE = ½mv2; KE = Kinetic Energy (N•m),
m = mass (kg), v = speed (m/s)
Newton: kg•m/s2
N•m = Joule (J)
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One way to think about energy is to consider
it as “stored work”
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Let’s try to identify the different kinds of
energy
Coin Toss
 After you bent the ruler, but before you let it go:
 After you let it go (rising), and before it hits the
ground (falling):
 At the peak (the highest the coin will go up before
it starts to come back down; hint: v = 0 m/s)
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Let’s try to identify the different kinds of
energy
Pole Vault
 While the pole vaulter is running
 When the pole vaulter uses the pole to spring
herself up (bends pole)
 When the pole vaulter is in the air and rising
 When the pole vaulter is no longer rising, but has
not started falling yet
 When the pole vaulter is falling down
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Child has 28 blocks (possibly in the middle of
the floor in her bedroom)
 Sometimes one or two blocks are elsewhere
(mom and dad’s room, living room), but there are
still 28 blocks total
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A weightlifter uses a force of 325 N to lift a set
of weights 2.00 m off the ground. How much
work did the weightlifter do?
 Want
 Given
 Formula
 Solve (units)
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How much energy is stored in a pole with a
spring constant of 15 N/m if it is deflected 1.6
m?
 Want
 Given
 Formula
 Solve (units)
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One of the highest pop flies every recorded in
baseball was about 172 m. What is the
gravitational potential energy of a baseball
with a mass of 145 g that is hit that high into
the air (g = 10 m/s2)?
 Want
 Given
 Formula
 Solve (units)
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A football player has a mass of 100.0 kg and
runs at a speed of 6.0 m/s. What is his kinetic
energy?
 Want
 Given
 Formula
 Solve (units)
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If champion pole vaulters can clear a 6.0 m
high bar with a 5.5 m long pole, why can’t
they vault over a 12 m high bar with a pole
11.0 m long?
What factors (variables) do you think limit the
height a pole vaulter has been able to attain?