Warm-Up: September 30th
What kind of potential energy is
this jellyfish probably using to
change into light energy?
http://www.youtube.com/watch?v=
1xkNPp6mzzI
WORK AND POWER>>>>>
Remember……. Work= F x d
Power=W/t
1) How much work is done by sliding a box
13 meters with a force of 2.5 N across the
floor?
2) How much work is done if you lift a box
that weighs 2.5N 13 meters straight up and
set it on a ledge?
3) How much power does it take if you lift the
box in #2 in 3.2 seconds?
The thing about work...
It’s hard.
How can we make it easier?
Simple Machines.
They help with work…they don’t do it for
you. (Those are robots)
Simple machines change the size of an
“input force” (the force you exert) or the
direction of that force, or both.
The point of simple machines is to be able
to use less input force. Work is still
being done, it’s just “easier.”
Simple Machines – 6 Types:
Levers
Class 1
Class 2
Class 3
Pulleys
Wheel and Axel
Inclined Plane
Wedge
Screw
The 6 Simple Machines
Inclined Plane
Screw
Pulley
Lever
Wedge
Wheel and Axle
Why is the work easier?
Simple machines give
you a mechanical
advantage. It’s the
“superpower” that you
get when you use one.
Mechanical Advantage (MA)– how
machines make work easier
 They increase the force you put
in (so you can use less force)
 change the direction of your
force
Force with Machines....
• Fe - Effort Force
(input)
The force you put
into a machine
Fr - Resistance
Force (output)
The force the
machine puts out
Fe
Fr
There are 2 kinds of
Mechanical Advantage
Ideal Mechanical
Advantage IMA – if no
work was lost to
friction
Actual Mechanical
Advantage AMA –
actual measured
advantage
Efficiency of a Machine:
Measured by how much the AMA is
divided by the IMA
Efficiency = AMA x 100 =
IMA
EXAMPLE
Lifting a dresser into a truck would take 700N of
force. But if you put a ramp of 20 feet, it would
reduce the amount of force needed to 350N.
That means the IMA (ideal) would be 2 (2 x the
force you applied)
But when we measured the amount of force
needed it was closer to 400N
That is an AMA 1.75
Efficiency = 1.75 = .88 x 100 = 88% efficient
2.0
REMEMBER – THE POINT OF
MACHINES IS TO USE LESS, NOT
MORE INPUT FORCE!
***The amount of work is the same
MA = Resistance Force
Effort Force
Inclined Plane
Inclined Plane

The Egyptians used simple machines to build the
pyramids. One method was to build a very long
incline out of dirt that rose upward to the top of the
pyramid very gently. The blocks of stone were placed
on large logs (another type of simple machine - the
wheel and axle) and pushed slowly up the long,
gentle inclined plane to the top of the pyramid.
Inclined Planes

Examples today
Inclined Plane Mechanical Advantage


The inclined plane
increases the
distance through
which the force must
move and reduces
effort force
W= F x d
Without ramp:
45Joules = 15N x 3m
Using ramp:
45Joules = 3N x 15m
15m
3m
Inclined Plane Mechanical Advantage

So if our distance was increased to 15m,
the amount of work is same, so the
amount of force used must be less

W= F x d
Without ramp:
45Joules = 15N x 3m
Using ramp:
45Joules = 3N x 15m
The Screw
Like the ramp, the screw increases
distance of work, reducing the
effort force.
Wedges
Two inclined
planes joined
back to back.
 Take a single
downward
force, redirects
it to two
directions
(splits things)

Lever – Mechanical Advantage
The MA of a lever is the ratio of the increase
distance on the input side (where you pushyour force) of the fulcrum to the length of the
lever on the resistance force side of the
fulcrum (machine's force)
Lever
.

Common examples
of levers include
crowbars, scissors,
pliers, shovels...
More Levers

tweezers,
arm,
hammers, and
shovels.
The Wheel and
Axle
 A rod (axle)
that turns a
wheel, (or the
wheel can turn
the rod)
WHEEL AND AXEL

Example: Fan
 The blades are
attached to the
wheel. When the
axel turns, the fan
blades spin.

Doorknob
Pulleys –Mechanical Adv.
A chain, belt , or rope wrapped
around a wheel.
Can either change the direction
or the amount of effort force
The more wheels and ropes,
the easier to pull (less force
needed)
Examples of
Pulleys
Simple Machines Video
http://www.watchknowlearn.org/Video.asp
x?VideoID=14008&CategoryID=1745