Transcript kinetic_potential PPT

Read over your notes on
pages 9 & 10 of your
science binder. Complete
the summary at the
bottom of page 10. Be
ready to share your
statements. If you finish
before others, use this
time to reduce your
notes.
S8P2
Students will be familiar with the
forms and transformations of
energy.
Element: S8P2.a
Explain energy transformation in
terms of the Law of Conservation
of Energy.
Element: S8P2.b
Explain the relationship between
potential and kinetic energy.
What is the relationship between
potential energy and kinetic energy?
Definition of Energy: Energy is the
ability to do work. Work is done
when a force causes an object to
move in the direction of the
force.
Energy is measured in the metric unit
known as a Joule.
One joule (J) equals one kilogram
times velocity squared
J = kg  v2
Three important types of
energy:
Kinetic
Potential
Mechanical
Kinetic Energy (KE) -The energy of motion
Examples:
a. Baseball being thrown
b. Skater racing around the ice rink
Formula for Kinetic Energy
Kinetic Energy (KE) = m

2
v2
Sample Problem
What is the kinetic energy of
an ice skater with a mass of
70 kilogram skating around
the ice rink at a speed of 2
m/s (meters per sec)?
FIND Kinetic Energy
GIVEN
FORMULA
SUB & SOLVE
This sample problem uses the "T" method of problem solving!
FIND Kinetic Energy
GIVEN
m = 70 kg
FORMULA
SUB & SOLVE
v = 2 m/s
This sample problem uses the "T" method of problem solving!
FIND Kinetic Energy
GIVEN
m = 70 kg
FORMULA
KE = mv2
2
SUB & SOLVE
v = 2 m/s
This sample problem uses the "T" method of problem solving!
FIND Kinetic Energy
GIVEN
m = 70 kg
v = 2 m/s
FORMULA
KE = mv2
2
SUB & SOLVE
KE = 70 kg x (2 m/s)2
2
KE = 70 kg x 4 m2/s2
2
KE = 280 kg  m2/s2
2
This sample problem uses the "T" method of problem solving!
Practice Using the T-method to solve these Kinetic problems.
#1) What is the kinetic energy of a bowling ball with a mass
of 4 kg and is moving at a speed of 3 m/s?
FIND
FORMULA
GIVEN
SUB & SOLVE
Practice Using the T-method to solve these Kinetic problems.
#2) A tennis ball has a mass of 0.2 kg. Serena Williams serves the
tennis ball with a speed of 9 m/s. What is the kinetic energy of the
tennis ball Serena is serving?
FIND
FORMULA
GIVEN
SUB & SOLVE
Interpreting the formula
without number
What can you tell out the kinetic energy
from the formula?
The more mass on object has the more
kinetic energy the object will have.
The less speed an object has the less
kinetic energy the object will have.
Practice:
Which has more KE -- a 2 kg ball
or a 4 kg ball assuming both
balls are moving with the same
speed?
Which has more KE -- a football
thrown with a speed of 1.3 m/s
or a football thrown with a
speed of 1.6 m/s?
Practice:
Which has more KE -- a 2 kg ball
or a 4 kg ball assuming both
balls are moving with the same
speed? 4 kg ball
Which has more KE -- a football
thrown with a speed of 1.3 m/s
or a football thrown with a
speed of 1.6 m/s? ball at 1.6
m/s
Definition of Stationary: Any
object with a speed of zero (it is
not moving) is said to be
stationary
What is the kinetic energy of a
stationary object? Zero joules
An object must be moving to
have kinetic energy
Energy in an object because of
its position, shape, or condition
When an object is picked up,
you give the object gravitational
potential energy (GPE) because
work was done against gravity.
Formula for Potential Energy
Gravitational Potential Energy (GPE)
GPE = weight x height
Caution--- Remember
mass(measured in grams) and
weight (measured in Newtons)
are not the same thing!
Sample Problem
What is the gravitational potential energy of a skier with a weight
of 450 newtons (N) who is at the top of a mountain 240 meters
high?
FIND
GPE
FORMULA GPE = weight x height
GIVEN
Weight = 450 N
SUB & SOLVE
GPE = 450 N x 240 m
Height = 240 m
GPE = 108,000 N  m
GPE = 108,000 J
UNITS NOTE: Weight is measured in Newtons (N)
Newton times meter (N  m) = Joule (J)
Interrupting the formula without
number-
What can you tell about the GPE from
the formula?
The more weight an object has the
more potential energy the object will
have.
The higher up the object is moved
(above the ground) the more potential
energy the object will have.
Practice:
Which has more GPE -- a 12N ball or
a 15N kg ball assuming both balls are
sitting on at the same level?
Which has more GPE -- a person on
the fifth floor of a building or a
person on the twelfth floor of a
building?
Practice:
Which has more GPE -- a 12N ball or
a 15N kg ball assuming both balls are
sitting on at the same level? 15 N ball
Which has more GPE -- a person on
the fifth floor of a building or a
person on the twelfth floor of a
building? person on the 12th floor
Mechanical Energy (ME) -- Total energy of motion
(kinetic) and energy of position (potential)
QUESTION #2
Formula for Mechanical Energy (ME)
Mechanical Energy (ME) = KE + GPE
Sample Problem:
A12 N book is sitting at the top of a book shelf 2 meters off the
ground. The book has a GPE of 24 J. Someone knocks the book
off the shelf and the book falls to the ground. When the book is
one meter off the ground, the book has a GPE of 12 J. At this
point the book is moving and it has 12 J of kinetic energy.
Compare the mechanical energy of the book at 2 meters (sitting
on the top of the book shelf) with the mechanical energy at 1
meter.
Sample Problem:
A12 N book is sitting at the top of a book shelf 2 meters off the ground. The book
has a GPE of 24 J. Someone knocks the book off the shelf and the book falls to the
ground. When the book is one meter off the ground, the book has a GPE of 12 J.
At this point the book is moving and it has 12 J of kinetic energy. Compare the
mechanical energy of the book at 2 meters (sitting on the top of the book shelf)
with the mechanical energy at 1 meter.
FIND
ME
GIVEN
GPE (at 2 m) = 24 J
KE (at 2 m) = 0 J
24 J
GPE (at 1 m) = 12 J
24J
KE (at 1 m) = 12 J
at 2 meters
mechanical energy
FORMULA ME = KE + GPE
SUB & SOLVE
ME (at 2 m) = 24J + 0J =
ME (at 1 m) = 12 J + 12 J =
Answer: Mechanical energy
equals the
at 1 meter