Transcript Slide 1

Energy
What do they all have in common?
Energy
• Defined as the ability to cause change!!
• Revisit the previous slide and explain how
each of these has the ability to cause change!!
2 Types of Energy
Kinetic Energy
Potential Energy
• Energy of motion.
• The energy of position
or condition.
• Several kinds of
Potential Energy:
– In order to have
Kinetic energy an
object must be in
motion(It must have
a velocity!!
1.
2.
3.
4.
Gravitational PE
Elastic PE
Chemical PE
Nuclear PE
Types of Potential Energy
• Gravitational Potential Energy(Peg) is the
potential energy an object has due to its
height.
– The higher an object, the more potential it has to
cause change!!
Mr. Eidson
Mr. Rodgers
Types of Potential Energy
• Elastic Potential Energy is the potential energy
an object has due to being stretched or
compressed.
Types of Potential Energy(cont.)
• Chemical Potential Energy is the potential
energy something has because of its chemical
makeup!!
Sodium tossed into pond!
Types of Potential Energy(cont.)
• Nuclear Potential Energy is the potential
energy of the particles inside an atomic
nucleus.
Kinetic Energy
Where:
KE = kinetic energy in Joules(J)
m = mass in kilograms(kg)
v = velocity in m/s
James Prescott Joule
1818-1889
Ex. A 1500 kg car moves down the road at 12 m/s.
How much kinetic energy does the car have?
Given:
m = 1500 kg
v = 12 m/s
KE = ?
KE = ½(1500kg)(12 m/s)2
KE = 108,000 J
Ex. A 350 kg boulder is rolling down a hill at 17 m/s.
How much kinetic energy does the boulder have?
Given:
m = 350 kg
v = 17 m/s
KE = ?
KE = ½(350kg)(17 m/s)2
KE = 50,575 J
A 1.5 kg football is thrown with a
velocity of 15 m/s. What is the
kinetic energy of the football?
A. 11.25 J
B. 22.5 J
C. 168.8 J
D. 337.5 J
A 2000 kg truck is moving down the
highway at 8 m/s. What is the kinetic
energy of the truck?
A. 8000 J
B. 16,000 J
C. 64,000 J
D. 160,000 J
Ex. A 3000 kg racecar has 200,000 J of kinetic energy
as it moves around the track. Determine the velocity
of the racecar?
Given:
m = 3000 kg
v=?
KE = 200,000 J
Ex. A 25 kg rock is thrown with a velocity of 2 m/s.
What happens to the kinetic energy of the rock if the
velocity is doubled?
Given:
KE = ½(25kg)(2 m/s)2
m = 25 kg
v = 2 m/s
KE = ?
KE = 50 J
?
KE increases by a
factor of 4!!
KE = ½(25kg)(4 m/s)2
KE = 200 J
Gravitational Potential Energy(PEg)
PEg = mgh = Fgh
Where:
PEg = Gravitational Potential Energy in Joules(J)
m = mass is kilograms(kg)
g = acceleration due to gravity(9.80 m/s2)
h = height in meters(m)
Fg = weight in Newtons(N)
If there are 2
equations,
how do I know
which one to
use??
I don’t know,
we should
probably ask
Hillary? She
thinks she
knows
everything!!!
Well, if you’re given
the mass(in kg), use
PEg = mgh
And if you’re
given
weight(in N),
use
PEg = Fgh
Ex. A 450 kg boulder rests on the edge of a 120 m
high cliff. Determine the gravitational potential
energy of the boulder.
Given:
PEg = mgh
m = 450 kg
PEg = 450(9.80)(120)
h = 120 m
g = 9.80 m/s2 PEg = 529,200 J
PEg = ?
Ex. A 90 N flowerpot sits on the edge of a 14 m
high window. How much potential energy does
the flowerpot have?
Given:
PEg = Fg h
Fg = 90 N
h = 14 m
PEg = ?
PEg = 90 N(14 m)
PEg = 1,260 J
Ex. To what height would you have to lift a 25 kg
barbell to give it 612.5 J of potential energy?
Given:
m = 25 kg
PEg = 612.5 J
g = 9.80 m/s2
A 4500 kg boulder rests on the edge of
a 40 m high cliff. What is the potential
energy of the boulder?
A.180,000 J
B. 1,764,000 J
C. 260,000 J
D.2,390,000 J
A 400 N box rests on a 2.5 m high cliff.
What is the potential energy of the box?
A. 1000 J
B. 4800 J
C. 9800 J
D. 14,200 J
Is it possible for one type of energy to
change to another type of energy?
Consider the picture to the left:
At point A, what type of energy
does the ball have?
Potential Only WHY?
At point B, what type of energy
does the ball have?
Both PE and KE WHY??
At point C, what type of energy
does the ball have?
KE only
WHY?
How did this happen?
Tomorrow:
You will design your own lab to answer the
following question……..
“Is there a relationship between Gravitational
Potential Energy and Kinetic Energy for a ball
tossed into the air(A Free-Falling Body)?
You will state a hypothesis(after discussion with
your group), design an investigation, analyze
data, state a conclusion!!!
Can other types of energy change?
WHY?
Where is PE and KE
highest and lowest?
Rank Potential Energy from high to low!
A-----C-------E----------D--------B
Rank Kinetic Energy from high to low!
B------D------E----------C--------A
Which Skier has the
highest Potential
energy?
Which skier has the
highest kinetic
energy?
Which Skier is moving
the fastest?
Where is the
potential energy the
greatest?
Where is the
potential energy the
least?
Where is the kinetic
energy the greatest?
Where is the kinetic
energy the least?
Which rock is moving
the fastest?
Law of Conservation of Energy
• As long as no unbalanced forces act on a
system of objects, the total energy in a system
will remain the same.
• Energy may change form, but it cannot be
created nor can it be destroyed!!
Mechanical Energy remains Constant:
• Total Potential and Kinetic energy.
– ADD THEM UP!!