Transcript Planet Earth - Madeira City Schools

Work & Energy
Chapter 12 Notes
Work
Work
has a specific meaning in
science - Work is done when a force
causes a change in the position of an
object
Work
The
equation for work is:
Work
= Force x distance
W=F*d
Work
Unit
for work is a Joule (J)
J=N*m
J = [(kg * m) / s2] * m
J = (kg * m2) / s2
Work Example
Find
the work done when a father
lifts his daughter up into the air if he
lifts her 1.5 m and uses a force of
160 N.
Power
Power
is defined as work/time
Power
= Work / time
P
= W / ∆t
Power
The
units for power is the Watt (W)
Watt
W
= Joule / second
= (kg * m2) / s3
Power Example
A
race car zooms down a race track
of length 200 m. The car has a force
of 400 N pushing it forward. The car
finishes the race in 5 seconds.
Find
the work done on the car
Find the power of this car
Energy
The
world around is full of energy
You can see it, hear it, possess it,
store it, etc
Living organisms cannot survive
without energy
Energy
Energy
The
The
is often defined as:
ability to do work
unit for energy is the joule
How
does this compare to the unit for
work?
Energy
Two
major types of mechanical
energy
Potential
Based
Kinetic
Based
energy
on position/configuration or an object
energy
on motion of an object
Potential Energy
Gravitational
Energy
Elastic
potential energy
stored by gravity
potential energy
Energy
stored by an object that
stretches
Potential Energy
Gravitational
Depends
object
potential energy
on the mass and height of an
PE
= mass x gravity x height
PE
=m*g*h
Potential Energy Example
Find
the PE of a 20 kg object
elevated 5 meters above the ground.
Kinetic Energy
Energy
of a moving object caused by the
motion of the object is called kinetic
energy
Depends
KE
on mass and speed of object
= (1/2) (m * v2)
Kinetic Energy Example
Find
the KE of a 400 kg object
moving with a speed of 5 m/s
Kinetic Energy
Does
KE depend more on mass or
more on speed?
Other forms of Energy
Non-mechanical
Solar
Electrical
Nuclear
Chemical
Light
Sound
energy types
Energy Transformations
Energy
another
can change forms from one type to
As a ball drops PE is transformed into KE
When a slingshot is fired PE is transformed
into KE
Flipping a light switch will transform electricity
to light
When a car slows KE is transformed into
thermal energy (due to friction)
Conservation of Energy
Law
states:
Energy
cannot be created
Energy cannot be destroyed
Energy can be transformed from one
form to another form
Conservation of Energy
Sometimes
it seems like energy is
“lost” or destroyed
Can
you explain where this energy went?
Conservation of Energy
Identify
the transformations of
energy for a pendulum as it swings
back and forth
Conservation of Energy
Identify
the transformations of
energy for a toy car that is wound up
and then released
Conservation of Energy
Describe
the energy transformations
of a truck as it slows to a rest as it
approaches a stop sign