Simple Machines

Jay Williams

QCC
Explains how
machines make work easier.
12.1 Describes six types of simple machines.
12.2 Recognizes the simple machines that make up a compound machine.
12.3 Describes the relationship between work, power, and time.
12.4 Explains what the science of bionics involves (STS).
12.5 Contrasts two methods of using electrical signals to trigger motion of a limb or other body processes (STS).

ITBS Objective(s)
Levels 12 & 13 & 14 Physical Science
The student demonstrates knowledge of the physical sciences, including an understanding of
simple machines.

INTRODUCTION
Machines make work easier by changing the size of the force applied to it, the direction of the force, or both. Simple and compound machines, along with advances in technology, have improved the overall quality of
life.
Vocabulary
SIMPLE MACHINE:There are three simple machines: the lever, the pulley, and the inclined plane.
The wheel and axle, the wedge, and the screw are modifications of the three simple machines and are also refered to as simple machines.

MACHINE: A device that makes work easier by icreasing force,increasing distance, or changing the direction of the force.
WORK: Force acting over a distance to move an object against some resistance. If nothing is moved then no work is done.
Work= F x D
(work= force x distance the object moved)
JOULE:
Measure of work the same as newton meters
POWER:
The rate over which work is done
or work over time
Power = work/time (or work rate)
FORCE :The push or pull that gives energy to an object.It may produce a change in the motion, shape or size of an object. It may be measured in the following units:
newtons,pounds, kilograms,grams
GRAVITY:
The force that every object exerts on the objects around it. The greater the mass the greater the gravity.
INERTIA:
An object's resistance to change in motion. The greater the mass the greater the inertia.
FRICTION:
Force that acts in the opposite direction of motion (rubbing).
It will cause an object to slow down and eventually stop.
RESISTANCE:
Gravity (in the form of the weight of the object), inertia, friction and any other force that must be overcome in order for the object will move.
EFFICIENCY:
The comparison between the amount of work put into a machine and the amount of work accomplished
MECHANICAL ADVANTAGE
Is the amount by which a machine increases force calculated by dividing the amount of work done by the amount of effort put into it.
M.A.=load/effort force
load = amount of work done
effort force= amount of effort put into it.
MA = Inclined plane length/Inclined plane height
Formula for finding the mechanical advantage of a pulley:
MA = the # of supporting straps
Formula for finding the mechanical advantage of a lever:
MA = the distance from the fulcrum on the larger side
the distance from the fulcrum on the shorter side

LEVER
A lever is a rigid bar that rotates around a single point. Downward motion at one end results in upward motion at the other end. Depending on where the pivot point is located, a lever can multiply either the force applied or the distance over which the force is applied. Levers can be either first class , second class, or third class levers.
FULCRUM
The fixed pivot point of a lever
EFFORT ARM
The part of a lever to which force is applied
RESISTANCE ARM
The part of the lever that bears the load or resistance
LOAD
The object to be moved or the resistance to be overcome in order for work to be accomplished.

A SCREW
A screw is a central bar with an incline plane wrapped around it to form a spiral .

PULLEY
A pulley is a rope or chain wrapped aound a grooved wheel.
A single pulley simply reverses the direction of a force. When two or more pulleys are connected together, they allow a heavy load to be lifted with less force. The trade-off is that the end of the rope must move a greater distance than the load.

INCLINE PLANE
An inclined plane is a simple machine with no moving parts. It is simply a straight slanted surface that multiplies force. ( Ex. a ramp.)

WEDGE:
A wedge is a modification of an inclined plane that moves . It is made of two inclined planes put together. Instead of the resistance being moved up an inclined plane, the inclined plane moves the resistance.

WHEEL and AXLE
A wheel and axle is a modification of a pulley. A wheel is fixed to a shaft. The wheel and shaft must move together to be a simple machine. Sometimes the wheel has a crank or handle on it. Examples of wheel and axles include roller skates and doorknobs.

Background
A machine is a device that does work.
Work is force acting over a distance to move an object against some type of resistance.If nothing is moved then no work is done.Work is required to act against resistive forces, such as friction, air resistance, and gravity. Work is force times distance against resistance. Work =FxD
Force to lift an object is usually the weight of that object unless using machine to decrease the force needed.When using a machine to change the force a springscale can be used to dertermine how much force or effort force is being exerted.
Place the springscale between the force (you) and the effort arm of the machine.
In the case of an incline plane between the force (you ) and the load.The units of measure used may be:
g/m
kg/m
joule
foot pound
If force is measured in kilograms and distance is measured in meters then work will be in kilograms per meter or kg/m. The same is true with grams and meters, feet and pounds (foot pounds) and so on.If force is in newtons and distance is in meters the unit of work will be newton meters or joules.
     When dealing with machines there are two kinds of work to which we refer; Work input (effort force) which is the work actually put into or applied to the machine and work out put which is the amount of work done by the machine.
If you ignore the work lost due to friction and a machines inefficiencies, the amount of work produced by a machine is always exactly the same as the amount of work put into the machine.
work input (effort force)----->[MACHINE]--------->work output
Then why use a machine?
The idea behind a good machine is that the work will seem easier because either the machine multiplies the effort force (x2,x3....),it increases the distance over which the force moves, or it can change the direction of the force. To find out how "good " or efficient a machine is we must find the mechanical advantage.
       Mechanical advantage is the amount by which a machine increases force against resistance.Machines are used to gain a mechanical advantage against the force of resistance. This can be calculated by dividing the amount of work output by the amount of effort force.When a machine takes a small input force and increases the magnitude of the output force, a mechanical advantage has been produced.
All machines are typically described by a power rating. The power rating indicates the rate at which that machine can do work upon other objects. Thus, the power of a machine is work/time for that particular machine. To determine the power of a machine, one must be able to calculate the work done by the machine and the time it takes to do this amount of work.This would be calculated by the formula Power = work/time . The units work much the same as did the units for work. force unit/distance unit/ time unit
Resistance
work input (effort force)----->[MACHINE]--------->work output
Theoretically Effort Force should equal work output but the work is required to act against resistive forces, such as friction, air resistance, and gravity.
Friction is a force that works against motion and is caused by the irregularity of two surfaces rubbing together and the pull of gravity. For example, it would be harder to pull an object across a sticky or rough surface than it would be to pull that same object across a smooth surface. . Because of friction more force may be required to move an object. It also works againstefficiency in that it causes wear and tear to occur in machines when parts rub against each other often enough.
Lubricants, wheels, bearings, and rollers can be used to reduce friction and increase efficiency

WORK ACTIVITY
ACTIVITY: How much work is done when an object is lifted?
MATERIALS: meter stick
newton spring scale
objects to lift
string
pencil and paper
1. Make a chart like the one below to record your data. __________________________________________________________________
OBJECT FORCE USED DISTANCE LIFTED WORK DONE
(NEWTONS) (METERS) (JOULES)
__________________________________________________________________
1._______________________________________________________________
2._______________________________________________________________

2. Attach an object to the spring scale.
3. Slowly lift or pull the object. Record how much force you used to pull or lift
the object (Newtons).
4. Measure the distance you moved the object. Record the distance in meters.
5. Find out how much work you did by using the formula, work=force x distance
the object moved. Record your answer on the chart.
6. Repeat steps 2-5 with other objects.
FRICTION ACTIVITY
Have the students attach an object to a spring scale and pull it across various surfaces such as sandpaper, cloth, pencils, corrugated cardboard, and polished wood and record the results.

   Would you rather bike up a steep hill or gentle hill to arrive at the same height? Given the same effort (energy expended by the biker), who gets to the top of a hill quicker? Who travels farther? What are the trade-offs?....
An inclined plane is a simple machine with no moving parts. It is simply a straight slanted surface . It spreads the work out over a greater distance.
Here Mr. Stick

Figure could have lifted the barrel
8 meters straight up or he could move it 12 meters over the incline.
Using the formula for work Work= F x D to determine which way produces more work.
200 newtons x 8 meters= 1600 newton/meters    or 133.3 newton x 12 meters =1600 newton/meters.
The amount of work produced is the same but as you notice the force required is decreased because the distance over which the force is exerted is greater.
The mechanical advantage of an inclined plane is equal to the length of the slope divided by the height of the inclined plane.

As an example, for the inclined plane above, assume that the length of the slope (S) is 30 feet and the height (H) is 3 feet. The mechanical advantage would be10.
How?
Mechanical Advantage = S/H = 30/3 = 10

INCLINE PLANE
ACTIVITY: What happens to the amount of work needed to move a resistance
when the distance of the inclined plane increases?
Materials:
spring scale
weight
ruler (1ft)
shoebox
yardstick
1. Place the shoebox on a tabletop.
2. Place one end of the ruler on top of the shoebox and the other end of the ruler on
the tabletop.
3. Put the weight on the lower end of the ruler.
4. Attach the spring scale to the weight.
5. Slowly move the weight up the inclined plane to rest on the top of the shoebox.
6. Read the spring scale as you move the weight.
7. Next replace the foot ruler with the yardstick.
8. Repeat steps 2 - 7.

   A lever is a rigid bar that rotates around a single point. Downward motion at one end results in upward motion at the other end. Depending on where the pivot point is located, a lever can multiply either the force applied or the distance over which the force is applied. Levers can be either first class , second class, or third class levers.
There three parts of a lever:

FULCRUM
The fixed pivot point of a lever

EFFORT ARM

The part of a lever to which force is applied
RESISTANCE ARM
The part of the lever that bears the load or resistance
LOAD
The object to be moved or the resistance to be overcome in order for work to be accomplished.
There are three types of levers.

FIRST CLASS
Examples of this
kind of lever are : the pry bar, see-saw,
hammer and pliers

SECOND CLASS
An example
of this kind of lever is :
the wheelbarrow and bottle opener .

THIRD CLASS An example of this kind of lever is :
the fishing rod

The mechanical advantage of a lever is the ratio of the length of the lever on the applied force side of the fulcrum to the length of the lever on the resistance force side of the fulcrum. Below the M.A. is 100:10 or 10:1.

ACTIVITY
MECHANICAL ADVANTAGE OF A LEVER
ACTIVITY: How does mechanical advantage change?
MATERIALS:
lever
variety of weights
1 wooden block
1 weigh block (record)
1. Place block on top of ruler.
2. Place fulcrum under ruler.
3. Place weights on ruler end, opposite of the block.
4. Add weights (effort force) until block moves.
5. Calculate total weight of effort force.
6. Use ratio to calculate mechanical advantage
7. Does the mechanical advantage change if you move the fulcrum?
Formula for finding the mechancial advantage of an inclined plane:
MA = Inclined plane length/Inclined plane height
LEVERS
ACTIVITY
1. Draw each type of lever, by using the items above, label the fulcrum, effort, and object to be moved (or force).
2. Find other examples of levers and classify them as first, second, or third class.

ACTIVITY: What happens when the distance is changed between
the fulcrum and the effort force?
MATERIALS
5 large washers taped together
30 cm ruler
pen
1. Place washers on top of ruler at the 1 cm mark.
2. Place the pencil under the ruler at the 10 cm.
3. Push down on the 30 cm mark (effort force).
4. Move pencil to 15 cm mark and again push down at 30 cm mark (effort force).
5. Compare your effort force in steps 3 & 4.
6. Move pencil to 20 cm mark and again push down (effort force).
7.What class lever is this?

LEVERS
MACHINES AT HOME
Not all long, skinny objects are levers. A lever is a simple machine so to be a lever it must use energy to move a load. Can you find ten levers in your home or classroom?
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A pulley is a modified lever.
A pulley is a rope or chain wrapped aound a grooved wheel. It can change the direction or the amount of force.
If you had an object to move you could lift it upward or you could use a pulley attached to the ceiling and pull down on the rope to move the object. The pulley changes the direction of the force which makes it "easier " to move the object.
Pulleys attached to stationary structures are called fixed pulleys.

Pulleys can also multiply force. If you attach the pulley to the object that you are moving (movable pulley) the object will move one meter for every two meters the force pulls.
A moveable pulley rises and falls with the load that is being moved. A single moveable pulley creates a mechanical advantage; however, it does not change the direction of a force.The mechanical advantage of a moveable pulley is equal to the number of ropes that support the moveable pulley. (When calculating the mechanical advantage of a moveable pulley, count each end of the rope as a separate rope).

A compound pulley is a moving pulley with a fixed pulley, attached to it. You can add multiple of these arrangements on the same rope to reduce the effort. However, you must attach all the moving pulleys together and put a resistance between them. For every rope attached to the compound pulley, or the group of compound pulleys, the effort is divided by that. The more you divide the effort, the greater distance you will have to pull the rope. You must multiply the rope length by the amount of rope going through the axle, just as I mentioned above. Just like levers, there is the work formula. Force times Distance equals work. W=FD You take the effort and multiply it by the distance you are raising the object to get the work required.
Types of pulleys

The Pulley

Purpose:To study the mechanical advantage and efficiency of a single fixed pulley, a single movable pulley, a double pulley system, and a combination pulley system.

M.E. = d(F)/h.

Procedure:For each of the systems in figures A -D:
1.Set up the pulley system shown.
2.Determine the weight of the mass to be raised.
3.Raise the mass by pulling on the spring scale. Carefully measure the height to which the mass is lifted. Enter this value in the chart provided.
4.Record the value on the spring scale needed to raise the mass at constant speed.
5.Measure the distance through which the scale was pulled in order to
raise the mass to the height recorded in step 2. Record this value in
the chart provided.
6.Calculate the mechanical advantage and the efficiency of your
system.

PULLEY SYSTEM MECHANICAL ADVANTAGE

A

B

C

D

Can you think of another way to determine the mechanical advantage of each of the pulley systems?________________________________________
IComment on any differences or similarities that you observe._________
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PULLEYS
ACTIVITY: What happens when you increase the number of pulleys?
Materials:
three students
two broom handles
one ten foot long piece of twine or rope
1. Have one student tie the end of the twine onto one of the broom handles.
2. Have two of the students stand about two and one half feet apart so that the broom handles are
held about two feet apart.

3. Wrap the twine around the broom handles twice.
4. Have the third student pull on the twine as the other two students try to hold the broom handles
apart.
5. Now wrap the twine around the broom handles two more times and repeat step 4.

PULLEYS 1
HYPOTHESIS
If we had to lift a heavy load, pulleys can make the job easier.
MATERIALS
1 board and pulley 15 weights 1 rope
1 small bucket 1 pulley 1 load
1 large bucket 1 clamp 2 hooks
PROCEDURE
1. Clamp the board to your desk.
2. Hook the rope to the small bucket.
3. Put the load in the small bucket.

4. Put the rope over the top of the board. See Figure 1.
5. Tie the loose end of the rope to the large bucket. Make the rope short enough so that the large bucket is near the board.
6. GENTLY put the weights into the large bucket one at a time until the load just lifts off the ground. If you can slide a piece of paper under the edge of the small bucket, you have added enough weights.
7. Record the number of weights you needed.
8. Take the weights out of the large bucket and take the buckets off the rope.
9. Repeat this experiment two more times: first use the setup in Figure 2 and then the one in Figure 3.

SETUP WEIGHTS NEEDED

No pulleys

1 pulley

2 pulleys

CONCLUSION
How can pulleys help us?
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PULLEYS 2
HYPOTHESIS
You don't get something for nothing! Pulleys make it easier to lift heavy loads, but at a price: you can't lift the load as fast.
MATERIALS
1 board and pulley 2 rulers 1 rope
1 small bucket 1 pulley 1 load
2 hooks 1 clamp
PROCEDURE
1. Prepare the setup as shown in Figure 1.

2. Hold the loose end of the rope right where it comes out of the pulley. The rope should be tight, but the load should still be on the floor.
3. Hold one of the rulers so that one end is right by your hand. See Figure 2.
4. Pull the rope 12 inches to the other end of the ruler and hold it here.
5. While you hold the rope still, have your partner measure the height of the bottom and record it.
6. Repeat these steps with the 2 pulley setup that we used in the previous experiment. Be careful to pull the rope exactly 12 inches

SETUP HEIGHT OF LOAD (inches)

1 pulley

2 pulley

DISTANCE

Clip the end of the yellow string to the bottom pulley block. Pass the string over the middle pulley of the top block.
Use the marker to mark where the string leaves the top pulley.
Lift the lower pulley block a fixed height (h). The holes in the Stand are 5 centimeters apart and you can use the holes as a height reference. Use at least 20 centimeters as your lifting height.
Measure how much string length (L) you had to pull to lift the lower pulley the chosen distance. You can measure this using the markers and a ruler.
Measure the force needed to lift the lower pulley block.
Record the lifting force, height difference for the lower pulley block (h), and string length (L) in the data table.
Rearrange the yellow strings so that you achieve a mechanical advantage of 2,3,4,5, and 6. For each combination record the height (h), force, and string length (L) you had to pull to raise the bottom pulley block the required height (h).

A1.1: To Do the Experiment:

Clip the end of the yellow string to
the bottom pulley block. Pass the string over the middle pulley of the top block.
Use the marker (cord stop) stop to hook the force scale to the string.
Measure the force it takes to slowly lift
the bottom pulley block.
This arrangement has one strand supporting the bottom pulley block. Record the force needed in the table
in the row corresponding to one strand.
Take the yellow string off and clip the end to the top block next. Pass the string around the middle pulley in the bottom block and back over the middle pulley in the top block.
Move the marker and measure the force
it takes to slowly lift the bottom pulley block.
Record this force in the row for two supporting strands.
Rearrange the yellow strings so that you get 3,4,5, and 6 supporting strands. Measure and record the force it takes
to lift the bottom pulley block for each new setup.
This arrangement has one supporting strand of the yellow string.

This arrangement has two supporting strands of the yellow string.
Amount of Force
to lift support bottom pulley strands
block (N)
1 ____________
2 ____________
3 ____________
4 ____________
5 ____________
6 ____________
A1.2: As you add more supporting strands, what happens to the force needed to lift the bottom block?
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A1.3: Write a rule which describes how the force changes with the arrangement of the strings.
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SCREW
The screw is an incline plane wrapped around a post. While this may be somewhat difficult to visualize, it may help to think of the threads of the screw as a type of circular ramp (or inclined plane).
The distance between two adjacent screw threads is called the pitch of a screw. One complete revolution of the screw will move it into an object a distance to the pitch of the screw. The mechanical advantage of a screw can be found by dividing the circumference of the screw by the pitch of the screw. This formula is shown below: Mechanical Advantage = Circumference/Pitch
Screws are often turned by another simple machines such as a levers or a wheels and axles.This makes the screw even more efficient.

SCREW
ACTIVITY: Which screw is the easiest to screw into a block of wood?
Materials: one block of wood
four screw the same length with various numbers of threads
1. Take the screw with the least number of grooves.
2. Screw it into the block of wood.
3. Take the screw with the second least number of grooves.
4. Screw the second screw into the block of wood.
5. Take the screw with second to the most grooves.
6. Screw it into the block of wood.
7. Take the screw with the most grooves.
8. Screw it into the block of wood.
The Screw
This simple demonstration shows how a screw is actually an inclined plane. You may want to do this as a demonstration for your class or have every student make their own.
Materials
Pencil
Paper
Colored felt tip marker
Scissors

Procedure
1. Cut a right triangle from the paper. The dimensions should be about 5 inches, by 9 inches, by 10.3 inches.
2. Use the felt tip marker to color the longest edge (10.3 inches) of the triangle.
3. Position the shortest side (5 inches) of the triangle along the side of the pencil and then evenly wrap the paper around the pencil by rolling the pencil.

WEDGE
A wedge is a combination of two incline planes.
The difference in the two is that an incline plane is used to increase the distance of a force and a wedge is used to change the direction of a force.

What does a wedge do for us?
When you place a steel wedge on top of a log and strike it with a heavy hammer in order to split the wood into pieces you hit the wide end of the wedge (you apply a force downward).The wedge moves into the log it spreads and splits the wood by generating a sideways force.

Wedges can be used to split or lift.
When you strike a wedge, you are applying a force which moves the wedge some distance in the direction of the force. By this movement, the wedge then moves a load (whatever is in contact with the slope)a certain distance according to the effort applied.
Wedges allow you to trade off effort (force applied) and distance by using different lengths and angles of the wedge surfaces. The steeper slope requires more effort force and less distance. A gentle slope requires less effort force and a longer distance.
The mechanical advantage of a wedge can be found by dividing the length of either slope (S) by the thickness (T) of the big end.

WEDGE
ACTIVITY:What happens when the wedge is pushed between the stack of books?
Materials:
four hard covered books
a wedge
a tabletop
1. Stack the books on the tabletop vertically.
2. Place the tip of the wedge between the second and third books.
3. Push the wedge between the books.
DRIVING NAILS provides a better demonstration of the "gross" wedge concepts. Hammer two nails into a uniform, hard piece of wood: one nail is fairly blunt (i.e. a "steep" wedge slope), the other nail has a sharp point. Which nail is easier to move into the wood? Given blows of equal force from a hammer, which nail travels further into the wood? **A useful classroom experiment could be developed by driving sharp and dull pencils (same type of pencil, both with sharp point) into styrofoam, flower foam, etc. What relationship is observed between effort and distance moved?
M.A. of a Wedge

The length of the slope is 10 inches and the thickness is 4 inches. The mechanical advantage is equal to ______________. As with the inclined plane, the mechanical advantage gained by using a wedge requires a corresponding increase in distance.

A wheel and axle is a modification of a pulley. A wheel is fixed to a shaft. The wheel and axle move together.A wheel and axle can be made even more efficient by adding a crank or handle on it. Examples of wheel and axles :
door knob steering wheel tricycle wheel
When either the wheel or axle turns, the other part also turns. One full turn of either part causes one full turn of the other part.
If you are turning the wheel anything attached to the axle will cover less distance in the same amount of time. If you put effort into the axle the wheel itself will travel farther in the same amount of time. so wheels and axles change the distance over which a force is applied.
The mechanical advantage of a wheel and axle is the ratio of the radius of the wheel to the radius of the axle. In the wheel and axle illustrated below, the radius of the wheel is seven times larger than the radius of the axle. Therefore, the mechanical advantage is 5:1 or 5

WHEEL AND AXLE
ACTIVITY:
How does the simple machine called the wheel and axle make work easier?
MATERIALS:
empty spool of thread
string
paper cup
20 pennies
2 pencils
tape
1. Push pointed end of pencils into each end of the thread spools (make sure they are
secure)
2. Suspend the pencils from the edge of a table with two loops of string--make sure
they are level. Tape the string to the table.
3. Punch holes at the top of each paper cup. Attach a 60 cm string to each cup. Mark
the cups A and B.
4. Tape the string attached to cup A to the pencil and wind all of the string onto the
pencil by turning the pencil away from you.
5. Tape the string attached to cup B to the thread spool . Turn the pencils toward you
to wind up all of the string onto the spool.
6. Place 10 pennies in cup A.
7. Cup B should be at its top position. Add pennies to cup B one at a time until it
starts to move slowly.
8. Observe the distance both cups moved.

BIONICS
Originally, the word "Bionics" derives from the terms "bio" and "electronics". Nowadays, the word is more generally used for a young and interdisciplinary research field which combines biology with the sciences of engineering, architecture, and mathematics.
The rapid advancement of technology and medicine has forged a new medium, electrical stimulation, for treatment of disabling conditions including deafness, blindness, tremor and spasticity, urinary incontinence, chronic pain, and functional restoration of paralyzed limbs. Neurostimulation products (bionics) are implantable devices that generate electrical pulses directed to nerves and muscles for the treatment of disabling conditions.

Assessment Recommendations

Constructs working models of simple and compound machines.
Designs an experiment that demonstrates potential and kinetic energy.

LINKS
http://www.uark.edu/depts/aeedhp/agscience/simpmach.htm
http://science.cc.uwf.edu/sh/curr/machine/machine.htm
http://sln.fi.edu/qa97/spotlight3/
http://www.mos.org/sln/
Leonardo/InventorsToolbox.html
http://www.ed.uri.edu:80/SMART96/ELEMSC/SMARTmachines/machine.html
http://www.galaxy.net:80/~k12/machines/index.shtml
http://physics.mtsu.edu/~plee/SCI_OUTREACH/pulley1u.html
http://www.phys.scasd.k12.pa.us/hopkins/Chpt6Pulleylab.html
http://www.virtualphysics.com/vp2/science.htm
http://risc.usi.edu/~msampson/simple.html
http://www.pausd.palo-alto.ca.us/k6science/levers/lp_q_a.html
http://www.cpo.com/CPOCatalog/RP/rp_sci.htm
http://www.necc.mass.edu/MRVIS/MR3_13/start.htm
http://www.san-marino.k12.ca.us/~summer1/machines/simplemachines.html
http://www.uark.edu/depts/aeedhp/agscience/simpmach.htm
http://www.flash.net/~powell2/simple.html
http://www.canlink.com/profbeaker/simple.html
http://home.augsburg.baynet.de/walter.fendt/physengl/physengl.htm
http://www.glenbrook.k12.il.us/gbssci/phys/makeups/hplabs.html

FIRST CLASS		Examples of this kind of lever are : the pry bar, see-saw, hammer and pliers
SECOND CLASS		An example of this kind of lever is : the wheelbarrow and bottle opener .
THIRD CLASS		An example of this kind of lever is : the fishing rod