Learning Resources LER 2442 Manual De Instrucciones página 9

In a third-class lever, the fulcrum point is also located on one
end, but this time the applied effort is in the center between
the fulcrum point and load. An example of this type of lever
is a fishing pole. When fishing, the arm acts as the fulcrum
point, the effort is applied to the center of the rod, and the
load is at the end of the fishing line. The load moves in the
same direction as applied effort. Set up the model with the
rod resting on one end of the fulcrum and place one wheel on
the other end. Lift up the center of the rod to demonstrate a
third-class lever (figure 4D). Notice how the load is raised in
the same direction as the effort.
Wheel and Axle (figure 5)
A wheel and axle is one of the most common and useful simple
machines. Its purpose is to move objects from one place to
another with very little effort. Movement is accomplished
by rolling an object while the wheel is turning on the axle.
Demonstrate this principle by creating the doorknob model
(figure 5C). Roll the wheel back and forth and watch the axle
turn.
The wheel and axle consists of a wheel with a rod, called
the axle, at its center. Cars, clock gears, wheelbarrows, and
doorknobs are just a few examples in which a wheel and axle
can be found.
Experiment with the wheel and axle by creating the car model
(figure 5E). Set a heavy object atop the car and roll it on a
surface. Notice how little effort is needed. Now, place the
same object on the same surface without the car. Push the
object along the surface. Notice how much more effort is
needed to move the same object over the same distance.
Definitions
effort amount of force applied to move an object
force any push or pull on an object
fulcrum the support on which a lever rests while moving or
lifting an object
inclined plane flat surface that moves an object from one level
to another with less force over a greater distance
lever a bar, rod, or other surface that rests on a fulcrum point
and lifts objects with less effort
load object that is moved
simple machine a machine that consists of very few or no
moveable parts that makes moving an object easier
pulley a cord or wire moving over a wheel or set of wheels that
changes the direction of applied force to an object making it
easier to move
wedge consists of at least one, but usually two, inclineds
put together to form a sharp point that splits or separates an
object
wheel and axle a wheel with a rod, called an axle, in the center
on which the wheel rotates in order to move objects
work amount of force exerted multiplied by the distance an
object moves
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