Transcript Kinetic and Potential Energy

KINETIC AND
POTENTIAL ENERGY
4.1.14-4.4.14
Do Now: Make the following table in your notes
Grab a Calculator
Things I know
Things I didn’t know
Questions I have
3
Kinetic Energy
•
4
How to think about the equation
•
5
Practice
• A 70 kg man is walking at a speed of 2.0 m/s. What is his
KE?
• A 1400 Kg car is moving at a speed of 25 m/s. How much
KE does the car have?
Potential Energy
• Potential Energy- energy that is stored as a result of
position or shape.
• Energy is stored when a musician pulls a string.
• Stored energy is converted to kinetic energy.
• Two types of potential energy
• Gravitational
• Elastic
Gravitational Potential Energy
• PE that depends on an objects height
• A diver has a lot of PE at the top of the diving board.
• GPE is dependent on mass, gravity and height
• PE= mgh
• The units are in Joules
Practice
• A 60 Kg person walks from the ground to the roof
of a 74.8 m tall building. How much gravitational
potential energy does the person have at the top
of building?
• The gravitational potential energy of a diver is
3000 J. Her mass is 45 Kg. What height is she
standing at?
Elastic Potential
• Elastic Potential-is the potential energy of an object that is
stretched or compressed.
• We will look more at this when we get to harmonics.
Exit Ticket
• What kind of energy is represented by an archer
stretching a bow string?
• What factors determine the gravitational potential of an
object?
• Can an object have both kinetic and potential energy?
• A pitcher throws a 0.145 Kg Baseball at a velocity of 30
m/s. How much kinetic energy does the ball have?
Do Now 4.7.14
• Calculate the potential energy of a 45 Kg rock at the top
of a 100 m hill.
• A Car is driving down the road under the place where the
rock is falling. It weighs 1500 Kg and is moving with a
velocity of 45 m/s. What is its Kinetic Energy?
Energy Conservation
• The law of conservation of energy states
that energy cannot be created or
destroyed.
• All of the energy we have is present on
earth it can only be converted from one
form to another
• This is the best evidence for ghosts!!!!
Potential to Kinetic
• The PE of an object is converted to KE as
an object falls.
Kinetic to Potential
• Pole vaulters convert KE to PE
Mechanical Energy
• Mechanical Energy= KE + PE
• If an object has a KE of 4500J and a PE of
1000J what is the ME?
Conversion of ME
• (KE + PE)beginning = (KE + PE)end
Practice
• (KE + PE)beginning = (KE + PE)end
• At a construction site a 1.5 kg brick is dropped from rest
and hits the ground at a speed of 26 m/s. Assuming air
resistance is negligible calculate the gravitational
potential energy of the brick before it was dropped.
Practice
• A 10 kg rock is dropped and hits the ground at a speed of
60 m/s. Calculate the gravitational potential energy of the
rock before it was dropped.
Practice
• A diver with a mass of 70 kg stands motionless at the top
of a 3.0 m high platform. Calculate the potential energy
relative to the water surface while standing on the
platform, and the speed when he enters the water.
Practice
• A pendulum with a 1 kg weight is a set in motion from a
position 0.04 m above the lowest point on the path of the
weight. What is the KE of the pendulum at the lowest
point?
As you watch
• Suppose you are an energy planner who is concerned
about the possibility of future shortages of electricity. Write
a paragraph (7 sentences) describing two proposals that
you think would help to avoid this potential problem.
Heat
• Heat is a transfer of thermal energy from one
object to another.
• Heat flows spontaneously from hot objects to cold
objects
• NOT the other way around.
Temperature
• Temperature is a measure of how hot or cold an object is
compared to a reference point.
• Freezing 0 degrees
• Boiling 100 degrees
• Temperature is related to the average kinetic energy of
the particles in an object due to their random motions
through space.
Thermal Expansion
• Occurs when particles move farther apart as temperature
increases.
• How does this relate to kinetic energy?
Specific Heat
• Specific Heat- the amount of heat needed to raise the
temperature of one gram of a material by one degree
Celsius.
• The lower a materials specific heat the more its
temperature rises when a given amount of energy is
absorbed by a given mass.