# Kinetic and Potential energy

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```					               Catalyst
• What is Newton’s 3rd Law? Give me an
example of the law?
Kinetic and Potential energy

Page 447
Go over homework
• Pg 377 Data analysis
• Pg 377 questions 1-7
• Energy: the ability to do work
• work is a transfer of energy
• measured in Joules= kgm2/s2
Kinetic Energy
• the energy of motion
• kinetic energy of any moving object
depends upon its mass and speed
– equation: Kinetic energy= half the mass times
the velocity squared
» KE= ½ mv2

http://www.brainpop.com/science/energy/kin
eticenergy/preview.weml
Practice Problem
• A 0.10 kg bird is flying at a constant speed
of 8.0 m/s. What is the bird’s kinetic
energy?
More Practice Problems
•   A 20kg dog is running at a constant speed of
16 m/s. What is the dog’s kinetic energy?
•   A 50 kg human is walking at a constant speed
of 4 m/s. What is the human’s kinetic energy?
•   A human has a kinetic energy of 3.1 J, and a
speed of 2.7m/s. What is the human’s mass?
•   A car has a kinetic energy of 6.3 J, and a
speed of 5.4 m/s. What is the car’s mass?
Potential Energy
• energy that is stored as a result of position
or shape.

http://www.brainpop.com/science/energy/pot
entialenergy/preview.weml
Gravitational Potential Energy
• potential energy that depends upon an
object’s height
• an object’s gravitational potential energy
depends on its mass, its height, and the
acceleration due to gravity.
– Potential energy (PE) = mgh
– g (on earth) = 9.8 m/s (N)
Practice Problem
• Suppose the diver at the top of a 10.0
meter high diving platform has a mass of
50.0 kilograms. You can calculate her
potential energy relative to the ground.
More Practice Problems
•   A bird is sitting on top of a 17 meter high tree branch.
The bird has a mass of 2 kg, what is its potential
energy relative to the ground?
•   A jaguar is sitting on a tree branch 4.3 meters from the
ground, waiting to attack its prey. The jaguar weighs
89kg, what is its potential energy relative to the
ground?
•   The potential energy for a 2.5 kg squirrel in the tree is
1,500 J. At what height is the squirrel at?
•   The potential energy for a diver is 4,900 J. The diver is
on top of a 15 meter high diving board. What is the
mass of the diver?
Other Forms of Energy
• Mechanical energy: energy associated
with the motion and position of everyday
objects
• the sum of the potential and kinetic
energies
– example: bouncing a ball, speeding trains etc
Homework
• Create a comic strip that either discusses
the differences between
– Kinetic energy and potential energy (include
equations)
– Newton’s 3 laws of motion
• Thermal Energy:
• The total potential and kinetic energy of all
the microscopic particles in an object.
– example: when an object’s atoms move
faster, it’s thermal energy increases and the
object becomes warmer
Elastic Potential Energy
• The potential energy of an object that is
stretched or compressed
– Normally springs back to its original state
• Chemical energy:
• energy stored in chemical bonds
– burning gasoline
• Electrical energy:
• energy associated with electrical charge
– ex flashlights, cds
• Electromagnetic energy:
• energy that travels through space in the
form of waves
– ex galaxies
• Nuclear energy:
• energy stored in atomic nuclei
– nuclear fission or nuclear fusion

Practice problems:
• Questions 6-9 pg 452
Exit Ticket
• Name and explain all of the energies
needed to heat a cup of water
Conservation of energy

Page 453
Conservation of Energy
• Energy can be converted from one from to
another
• Energy conversion: the process of
changing energy from one form to another.
• The law of conservation of energy states
that energy cannot be created or
destroyed
• Gravitational potential energy of an object
is converted to the kinetic energy of
motion as the object falls
Energy conservation Equations

•     Mechanical energy = KE + PE
•     (KE + PE)beginning = (KE + PE) end
•      KE beginning = PE end
•      PE beginning = KE end
Practice Problem
• At a construction site, a 1.50 kg brick is
dropped from rest and hits the ground at a
speed of 26.0 m/s. Assuming air
resistance can be ignored, calculate the
gravitational potential energy of the brick
before it was dropped
More Practice Problems
• At a playground, a 3.4 kg ball is dropped from
rest and hits the ground at a speed of 28 m/s.
Assuming air resistance can be ignored,
calculate the gravitational potential energy of the
ball before it was dropped.
• At a hospital, a 1.8 kg stethoscope is dropped
from rest and hits the ground at a speed of 14
m/s. Assuming air resistance can be ignored,
calculate the gravitational potential energy of the
stethoscope before it was dropped.
• Einstein’s equation E = mc 2, says that
energy and mass are equivalent and can
be converted into each other. (c = speed
of light 9 x 1013 J
•     energy is released as matter is
destroyed, and matter can be created from
energy.
Practice Problems
• 9 and 10 on page 459.
Finish Newton’s Laws
• Create a mini comic strip that explains and
demonstrates
– Newton’s 1st, 2nd, and 3rd laws

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