Transcript Chp 15 PPT FINALx

Chapter 15
Energy
Windup Toy
•http://www.youtube.com/watch?v=
xwCUzYuiTdk
Energy & Its Forms
15.1
Avalanche Questions
•Where did the energy of the
avalanche come from?
•Where did it go?
Definitions
• Work
• Done when a force moves an object
through a distance
• A transfer of energy
• Energy
• The ability to do work
• Energy is transferred by a force moving
an object through a distance
Measuring Energy
•SI Unit of Energy
• Joules (J)
• 1 Joule = 1 Newton-meter
•Newton-meter
• The work done when an object is
moved 1 meter by 1-Newton force
Two General Types of
Energy
Kinetic Energy
• Energy of Motion
• Depends on mass
& speed
• Formula
Potential Energy
• Energy that is stored as
a result of position or
shape
• Energy with the
potential to do work
• Examples:
• Lifting a book in the
air
• Plucking a string
Parts of KE Formula
• K = Kinetic Energy (measured in Joules)
• m = mass (measured in kilograms)
• v = speed (measured in meters per
second)
Why would tripling the
speed at which a car is
moving have a greater
effect on its kinetic
energy than tripling its
mass?
KE Practice Problems
1. A 0.10 kg bird is flying at a constant speed
of 8.0 m/s. What is the birds kinetic
energy?
2. A 70.0 kg man is walking at a speed o 2.0
m/s. What is his kinetic energy?
3. A 1400 kg car is moving at a speed of 25
m/s. How much kinetic energy does the
car have?
4. A 50.0 kg cheetah has a KE of 18,000
Joules. How fast is the cheetah running?
Gravitational Potential
Energy
Gravitational PE
• PE that depends upon
an object’s height
• Increases as an object
is raised to a higher
level
• Depends on an objects
mass, height, and
acceleration due to
gravity
Formula
PE = mgh
• m = mass (kg)
• g = acceleration due
to gravity (9.8 m/s2)
• h = height (meters)
Gravitational PE Practice
Problems
#1
#2
• A diver is at the
top of a 10.0
meter-high diving
platform and has
a mass of 50.0
kg. What is her
gravitational PE?
• The same diver is
standing on the
ground. What is
her gravitational
PE? Why?
Elastic Potential Energy
•The potential energy of an object
that is stretched or compressed
•Elastic means something springs
back to its original shape after being
stretched or compressed
•Rubber bands…
•Investigating Elastic PE Lab (p450)
Forms of Energy
• Mechanical Energy
• Thermal Energy
• Chemical Energy
• Electrical Energy
• Electromagnetic Energy
• Nuclear Energy
Mechanical Energy
•Energy associated with the motion
and position of everyday objects
•Equal to the sum of KE and PE
Thermal Energy
•Matter is made of atoms that are in
constant motion
•The potential and kinetic energy of
all of the atomic particles in an
object make up its thermal energy
Chemical Energy
•The energy stored in chemical
bonds
•When bonds are broken, energy is
released
Electrical Energy
•Energy associated with electrical
charges
Electromagnetic Energy
• A form of energy that travels through
space in the form of waves
• The sun emits electromagnetic energy
• Capable of traveling long distances in
air and space
Nuclear Energy
•The energy stored in atomic nuclei
•Nuclear energy can be used to
generate electricity
Energy Conversion
& Conservation
15.2
An energy conversion
story…
•Meteor story, p 453 (read as class)
Energy Conversion
•Energy can be converted from one
form to another
•Energy conversion is the process of
this change
The story of a match…
Striking a match
Conservation of Energy
•Law of Conservation of Energy
• Energy cannot be created nor
destroyed
•Energy changes from one form to
another, but the total amount of
energy remains unchanged
An example…
•You are riding your bike, pedaling at
a constant rate, but then you stop
pedaling and coast. You eventually
come to a stop. Where did your
kinetic energy go?
PE to KE
•Gravitational PE is converted to KE
as an object falls to the ground
•Elastic PE to KE… Slinky TIME!
Energy story of a hungry
sea gull…
•Write a quick story about how a sea
gull could crack open an oyster
shell.
•Energy terms to consider:
Gravitational PE, KE, Chemical
Energy (in the form of Gull food)
Conversion Calculations
•Mechanical Energy = PE + KE
•Can be applied to any mechanical
process (which is any action, for
example, a sea gull flying an oyster
high into the air and then dropping
it on a rock)
•In these calculations we assume
friction is negligible
Conservation of
Mechanical Energy
(KE + PE)Beginning = (KE + PE)End
Conservation Example
•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. At what height was
the brick dropped from.