Download There are two forms of energy that we deal with on the planet earth

NRG
Stored and moving, not measured the same.
NRG
There are two forms of energy that we deal with on the planet earth everyday.
They are :
Potential Energy
Kinetic Energy
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Potential Energy:
Energy that is stored due to the position of an object.
This position is in relation to a
reference or zero point.
Because of this, NRG is stored by doing
work against another force.
Gravitational Potential Energy
• Energy stored in an object due to its position above the ground.
Work is done against gravity and stored in
the new position of the body.
• The ground is used as a reference point for measurements.
Height
Ground is where Potential
NRG can be zero
2
Work is done against gravity and stored in
the new position of the body.
Height
Ground is where Potential
NRG can be zero
If the body falls, the Potential NRG gained
by doing work against gravity is regained by
gravity as it does work.
Potential NRG : PE
Gravitational Potential NRG can be calculated.
PE = mgh
PE = Potential Energy
m = mass in kilograms
g = 9.8 m/s/s
h = height of the object above the ground.
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Gravitational Potential NRG Example 1
A book with a mass of 10 kg sits on a shelf 2 m above the ground. Find the potential energy for the book.
Given : m =
h=
g = 9.8 m/s2
Equation : PE = mgh
Solve : PE =
NRG
Kinetic Energy – The energy of motion.
Any object with mass, that is in motion, has kinetic energy.
If an object is not in motion, it does not have any kinetic energy.
If the object does not have mass, it does not have any kinetic energy.
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NRG
Kinetic Energy Equation
2
KE = ½ mv
Where
KE = kinetic energy in J
m = mass of the object in kg
v = speed of the object in m/s
The units of Kinetic Energy are Joules
Energy
Find the kinetic energy of a car with a
mass of 300 kg traveling at 5 m/s.
Given : m =
v=
2
Equation : KE = ½ mv
KE =
KE =
The car has a kinetic energy of _________ J
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NRG
Find the kinetic energy of a car with a mass of 300 kg traveling at 10 m/s.
Given : m =
v=
Equation : KE = ½ mv2
KE =
KE =
What happened to the amount of kinetic energy as the velocity was doubled?
NRG
Any increase in mass causes the same increase in kinetic energy.
From the previous example, when the
speed doubled in size, the energy
quadrupled. Why?
Kinetic energy depends on mass and
velocity. But the velocity component is
squared.
A change in velocity results in the NRG
changing by the square of the change
in how fast the body is moving.
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Change in Kinetic Energy
When the speed of a car is increased, the kinetic
energy increases.
A force is responsible for any change in velocity.
That force acts over a displacement, so work is
done by the force.
Work done = change in kinetic energy
W = KEf - KEi
Change in Kinetic Energy
For the car in our example
The car went from having ____ J to _____ J
of energy.
Change in kinetic energy = _______J
This was the work done by a force to
accelerate the car from 5 m/s to 10 m/s.
Work done = _________ J
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Change in Kinetic Energy
Looking at the results, does a doubling of the velocity
equal a doubling of the kinetic NRG?
∆KE = 3750 J when the car goes from
0 m/s to 5 m/s.
When the velocity is increased by 5 m/s to 10 m/s,
∆KE =11,250J
Doubling the speed requires doing 3 times
the work and the car will have 4 times the
NRG.
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