The Six Simple Machines Notes
Inclined Plane: a flat, sloped surface
 How it works: it allows you to exert your input force over a longer distance. The input force needed is
less (force that you push or pull an object) than the output force (force you would need to lift the object
without the inclined plane).
 Mechanical advantage: is determined by taking the length of the incline divided by the height of the
incline.
 Which has a better mechanical advantage, an inclined plane with a shorter or
longer length?
Ex. A ramp, this makes it much easier to push a grocery cart over a curb to do the job.
Wedge: a device that is thick at one end and tapers to a thin edge at the other end.
 How it works: you move the inclined plane itself. An ax handle exerts a force on the blade, which is the
wedge. This force pushes the wedge down into the wood. The wedge exerts an
output force at a 90 degree angle to its slope, splitting the wood. Wedges change
both direction and force.
 Mechanical advantage: determined by dividing the length of the wedge by its
width. The longer and thinner the wedge the greater the mechanical advantage.
 Why are sharp knives better than dull knives?
Ex. Blade of an ax, zipper
Screw: cylinder with a spiraling thread
 How it works: the input force you exert on a screw is increased because the threads
on the screw act like an inclined plane to increase the distance over which the force is
applied. A screw increases you input force by applying it over a longer distance.
 Mechanical advantage: determined by taking the length of the threads divided by
the length of the screw. The closer the threads the greater the mechanical advantage.
Ex. Bolts, light bulbs, jar lids
Wheel and Axle: two circular or cylindrical objects fastened together that rotate about a common axis. The
object with the larger axis is the wheel, and the object with the smaller radius is the axle.
 How it works: think about using a screwdriver, when you apply an input force to turn the handle or
wheel. Since the wheel is larger than the shaft, or axle, the axle rotates and exerts a
large output force. The wheel and axle increases your force, but you must exert your
force over a longer distance.
 Mechanical advantage: found by dividing the radius of the wheel by the radius of the
axle.
Ex. Screwdriver- handle is the wheel and shaft is axle, door knob, and a car’s steering wheel.
Pulley: grooved wheel with a rope or cable wrapped around it.
 How it works: you use a pulley by pulling on one end of the rope, this is the input force. At the other
end of the rope, the output force pulls up on the object you want to move. A pulley can make work
easier in two ways. It can decrease the amount of input force needed to lift
a heavy object. It can also change the direction of your input force.
 Mechanical advantage: is equal to the number of sections of rope that support the object.
Ex. Fixed pulley- top of flag pole
Moveable pulley- crane
Lever: rigid bar that is free to pivot, or rotate, on a fixed point. The fixed point on a lever is called the fulcrum.
There are three classes of levers which differ in the positions of the fulcrum, input force, and output force.
 How it works: when you push down on a lever, you exert an input force on the handle, and the lever
pivots on the fulcrum. The result is the tip of the lever pushing up, and exerting an output force on the
object. A lever makes work easier by both increasing your input force and changing the direction of
your input force. Levers allow you to use a smaller force.
 Mechanical advantage: determined by dividing distance from the fulcrum to the input force by the
distance from the fulcrum to the input force by the distance from the fulcrum to the output force.

First class: Fulcrum is between the input and out put forces. They always change the direction of the input
force. If the fulcrum is closer to the output force, they also increase the force. If the
fulcrum is closer to the input force they also increase distance.
Ex. scissors, pliers, & seesaws
Second class: Input force is furthest from the fulcrum. They increase force but do not change the direction of
the input force.
Ex. doors, nutcrackers, & bottle openers
Third class: output force is furthest from the fulcrum. They increase distance, but do not change the direction
of the input force.
fishing poles, shovels, & baseball bats