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WORK AND ENERGY
CHAPTER 9
9.1 WORK, POWER, AND
MACHINES
• This is an ad which used a
Rube Goldberg type
application….many simple
machines working together to
accomplish a simple task:
http://www.daboyz.org/hon
da/
• The film is real and took 606
takes (no digital imaging).
Two cars were disassembled
for the parts in the film.
• The film cost six million
dollars and took three
months to complete.
WORK - ___________________
(W = F x d)
TRYING TO LIFT THE
OBJECT BUT IT DOES
NOT MOVE….IS
WORK BEING DONE?
JOULE – a unit to describe work
one JOULE = a NEWTON moving one METER
If you lift one ______ from
your waist to over the top
of of your head you have
done one JOULE of work.
POWER - _________________
(P = W/t)
Running up the steps and
walking take the same
amount of work….but
which requires more
power?
WATT – a unit to describe power
one WATT = one JOULE of work in one SECOND
If you quickly move an object
weighing one newton from
your waist to over your
head in one ______ you
have done one WATT of
work.
MACHINES make work easier but
do not make less work.
WORK INPUT ALWAYS
EQUALS WORK
OUTPUT.
MECHANICAL ADVANTAGE - _______
(MA = output force/input force)
or
(MA = input distance /output distance)
Machines with a MA of
more than one
multiply force and
those with a MA of
less than one increase
the distance and speed.
1. A spring scale is used to measure
force and the unit of force is…
1. Joules
2. Watts
3. Newtons
2. A meter stick is used to measure
distance and the unit is …
1. Newtons
2. Meters
3. Grams
3. Work is equal to force times
distance and the label is …
1. Newtons
2. Grams
3. Joules
4. Power is equal to work divided
by time and the label is …
1. Watts
2. Joules
3. Newtons
5. Power is the ___ at which
work is done.
1. Speed
2. Rate
6. Not including friction the work
into a machine is always ___ work
out.
1. Less than
2. Equal to
3. Greater than
7. Including friction the actual
mechanical advantage is always ___
the ideal advantage.
1. Greater than
2. Equal to
3. Less than
9.2
Make a chart in your notebook similar to this one and label it
SIMPLE MACHINES. Place the name of each simple
machine at the top of a column and then draw a picture of each
under its name. Then identify several example of each type of
simple machine.
Lever
E
Pulley
R
Fly
swatter
Wheel ….
& axle
….
…..
THE LEVER
(THREE CLASSES)
• FIRST - _____ in the
middle.
• SECOND - _____ in the
middle.
• THIRD - ______ in the
middle.
THE PULLEY
(A MODIFIED LEVER)
A SINGLE FIXED PULLEY
has a MA of ____.
A SINGLE MOVABLE
PULLEY has a MA of ___.
MULTIPLE PULLEYS can
have various MA’s.
THE WHEEL AND AXLE
(A LEVER OR PULLEY ON A SHAFT)
• Mechanical Advantage
depends on size of wheel
and size of axle.
• Some are designed for
power.
• Some are designed for
speed.
THE INCLINED PLANE
A long gradual slope has a
larger MA than a short
steep slope.
THE WEDGE
(A DOUBLE INCLINED PLANE)
• The mechanical
advantage depends on
the length of the slope
and how wide the
wedge is.
• Long skinny wedges
have _____ M.A.
THE SCREW
(AN INCLINED PLANE WRAPPED
AROUND A CYLINDER)
• Steepness of slope determines
the M.A.
• A steep slope has a _____ M.A.
COMPOUND MACHINES - ______
9.3 ENERGY
•
Creation of the Sun, Moon, and Plants
by MICHELANGELO
POTENTIAL ENERGY - _________
• GRAVITATIONAL
POTENTIAL ENERGY
depends on mass and
height. More MASS or
more HIEGHT equals more
potential energy.
KINETIC ENERGY -_____________
Depends on mass and speed
but more on speed.
EXAMPLES OF POTENTIAL
AND KINETIC ENERGY
MECHANICAL
GRAVITY
ELASTIC
MOVING AIR(Bernouli)
SPRINGS
NONMECHANICAL
LIGHT
ELECTRICAL
CHEMICAL
NUCLEAR
SOUND
HEAT
9.4 CONSERVATION OF
ENERGY
POTENTIAL ENERGY CAN
BECOME KINETIC ENERGY
A ____ at the top of a
hill has potential
energy.
KINETIC ENERGY CAN BECOME
POTENTIAL ENERGY
A _____rising to the top of
a hill has kinetic energy.
OTHER ENERGY CHANGES
When potential and kinetic
energy transformations are
taking place some energy is
lost as HEAT energy or
SOUND energy.
The LAW OF CONSERVATION OF
ENERGY
Energy cannot be ______ or _______.
God created the universe with energy.
EFFICIENCY OF MACHINES _______________________
Not all of the work done by
a machine is useful work.
No machine is 100%
efficient.
Perpetual motion machines
are impossible.