Simple Machines
Physical Science Georgia Performance Standards:
SPS7a. Identify energy transformations in a system (e.g. lighting a match.
SPS8e. Calculate amounts of work and mechanical advantage using simple machines.
Created by:
Christy Dion
Paulding County High School
Dallas, Georgia
What is a simple
machine?
A simple machine is a machine that does work with only one
movement of that machine.
There are 6 basic simple machines:
1) Screw
4) Wedge
2) Lever
5) Pulley
3) Inclined Plane
6) Wheel & Axle
Levers
A Lever is a bar that is free to pivot
around a fixed point.
There are three types of levers:
Levers: what they
do...
Any tool that pries something loose is a lever.
A lever is an arm that pivots (or turns) against a fulcrum (or point).
Think of the claw end of a hammer that you use to pry a nail loose.
It's a lever.
It's a curved arm that rests against a point on a surface. As you
rotate the arm it pries the nail from the surface.
First Class Lever
A see-saw is
an example.
In a first class lever, the farther away from the fulcrum you apply the force,
the easier it is to lift up objects.
The closer to the fulcrum you apply the force, the more effort you need to
lift up the resistance.
The resistance goes in the opposite direction of the effort.
If a person pushes down, the resistance goes up, and if a person pushes
up, the resistance goes down.
Second Class Lever
A wheel
barrow is an
example.
A second class lever is a lever in which the resistance is located between
the fulcrum and the effort.
A second class lever always increases the effort force.
The fulcrum is the wheel and resistance in a wheelbarrow is the object
being moved while the person pushing the wheelbarrow supplies the effort.
Third Class Lever
An example is
a person's
arm.
A third class lever always decreases the effort force.
The effort is between the resistance and the fulcrum.
The fulcrum is the elbow, the biceps provide the resistance and the effort is whatever
is being lifted.
The distance from the elbow to the biceps is the effort arm and the distance from the
elbow to whatever one is trying to lift is the resistance arm.
A third class lever is always a disadvantage.
Determining Lever Class
FLE Rule
·First Class Lever - Fulcrum in
the center
·
·Second Class Lever- Load in
the center
·
·Third Class Lever - Effort in the
center
Use the objects on this page to show each of the levels of
levers.
Ideal Mechanical Advantage of
a Lever
The ideal mechanical advantage (IMA) for any simple machine can be
calculated by dividing the input distance by the output distance. For a lever,
the input distance is the length of the input arm and the output distance is the
length of the output arm.
length of input arm (m)
= length of output arm (m)
Ideal Mechanical Advantage
Lin
IMA =
Lout
Let's Practice:
John uses a lever to lift a weight of 5 N. The input distance (where the
input force is applied) is 50 cm. The output distance (where the output
force is applied) is 5 cm. What is the ideal mechanical advantage of the
lever?
IMA
= input distance
of lever output distance
Know
Setup
Solve
Input distance = 50 cm; output distance = 5 cm
IMA =
IMA = 10
50 cm
5 cm
Let's Practice:
Howard uses a pulley system to raise a bucket from a well. He pulls
his end on the rope 5 m and the bucket is raised 2.5 m. What is the
ideal mechanical advantage of this pulley system?
IMA= input distance
output distance
Know
Setup
Solve
Input distance = 5 m; output distance = 2.5 m
IMA =
IMA = 2
5 cm
2.5 cm
Pulleys
A pulley is a grooved wheel with a rope, chain, or cable
running along a groove.
A movable pulley is one where the
end of the rope is fixed and the
wheel is free to move.
A fixed pulley
changes only the
direction of your
force.
Ex. flagpole
Block & Tackle
Pulley
A block and tackle pulley consists of movable and
fixed pulleys together.
The IMA of a pulley system is equal to the number of weight segments that support
the weight.
Identify the type of pulley below?
Click on the flashing images to begin.
Wheel & Axle
A wheel and axle is a simple machine consisting of
a shaft or axle attached to the center of a larger
wheel so that the wheel and axle rotate together.
The wheel
and axle
move
Ideal Mechanical
Advantage
of can
Wheel
and objects
Axle: across a
distance.
IMA =
Radius
of wheel
(m)the axle causing movement.
The wheel
turns
IMA
Radius of axle (m)
formula
rw
IMA =
ra
Let's Practice
When making mousetrap cars, wheels are very important, some wheels are larger than others.
Pretend one car has the following measurements for their wheels: the radius axle (the small
wheel) measured only 1 cm. The radius of the larger wheel (the one that touched the
pavement) measured a whopping 10cm. What was the mechanical advantage of these large
wheels?
Formula:
Radius wheel (rw)
Radius axle (ra)
IMA =
10 cm
1 cm
setup
IMA =
solve
IMA = 10*
* this means with each turn of the axle you get 10 times the distance
Inclined Plane
An inclined plane is a sloping surface such as a
ramp that reduces the amount of force required to
do work.
For example a board is a plane, but lying
Mechanical Advantage of an
Inclined
flat
on the Plane:
ground its not likely to help
you do work.
IMA =
length of slope (m)
If slanted it can help you move object
height of slope (m)
across distances.
IM
Form
IMA=
l
h
Ex. Lifting a heavy box onto a loading
dock is easier with a ramp.
The Screw
If you take an inclined plane and wrap it around a
cylinder you get a screw, another simple machine.
The IMA of a screw is related to the spacing between the
threads.
The IMA is larger if the thread are closer together. However, if there are more
threads it takes longer to drive the screw into the material.
The inclined
plane is the
threads of the
screw.
The Wedge
A wedge is an inclined plane with one or two
sloping sides. It changes the direction of the
input force.
A knife blade is a wedge, as you cut an
apple it pushes the apple halves apart.
A wedge is an object that can be used to
push objects apart.
Let's Practice
You got roped into helping your parents' friend move. You are loading some pretty
heavy boxes, but luckily they have a ramp on the back of the truck. The truck is 1.5
meters off the ground and the ramp is 6 meters long. What is the IMA of this ramp?
IMA =
setup
solve
length of slope
height of slope
IMA =
IMA = 4
6m
1.5m
See examples of simple machines in
your everyday life at this website!
http://edheads.org/activities/simple-machines/
Resources
1)
2)
3)
4)
5)
wikipedia.org
google images
http://www.mswipc.com/problem_sets/mechanical_ad/mechanical_advantage_samples.htm
http://www.bristol.k12.ct.us/page.cfm?p=6620
McLaughlin, Thompson, & Zike. "Physical Science." Glencoe Science, McGraw Hill. 2008.