When we look at automobiles, boats, airplanes, and other
mechanical things we use every day; it is interesting to know what
makes them work. It is simply, the application of simple machines.
There are six basic simple machine types. They are the pulley, the
wedge, the wheel and axle, the inclined plane, the lever, and the
screw. Each simple machine has its own application and can be
combined with other simple machines into a system. Some simple
machines can lift things, while others push things apart. Some are
adapted into gears and other functional machines. One thing all
simple machines do is make things easier for people.
To understand how simple machines make things easier, we must
first understand the concepts of force and work. Force
is an action or effort that changes the motion of an object by
making it move, speeding it up, or slowing it down. Work is
the result of a force overcoming resistance - a larger force
overcoming a lesser force. Work is force acting over
distance. For example, if you lift a 50 pound weight off the
floor and place it on a shelf that is 6 feet off the floor, you
have performed 300 foot-pounds of work. You have exerted a force of
50 pounds over a distance of 6 feet. Simple machines let you apply
less force to accomplish desired work.
How is the effectiveness of a simple machine measured? It is
measured by determining the mechanical advantage of the
machine. Mechanical advantage is the amount of effort that a simple
machine supplies in doing work. It is a mathematical calculation
based on the relationship of the amount of force you apply compared
to the amount of resistance there is to the force. Simply, it is
how much the machine helps you do work by trading force for
distance. The equation used to calculate mechanical advantage
MA = Force needed without the simple machine/Force needed with
the simple machine
MA = Mechanical Advantage
A man lifts a rock weighing 500 pounds by standing on the end of
a lever. When the man later stood on a scale and weighed himself,
he weighed in at 100 pounds. How much mechanical advantage did the
lever provide to the man in lifting the rock?
MA = 500 pounds/100 pounds = 5
Conclusion: The man's body weight was magnified 5 times by using
the lever as a simple machine to lift the rock.
A person wants to use a lever to lift a large piece of
machinery. The person uses a lever that was previously used to lift
another piece of similar machinery and will be set up identically
for this lift. The mechanical advantage in the last set up was 8.
The machinery weighs 800 pounds. What force or weight must the
person place on the lever to move the machinery?
Estimate the answer:
than 50 pounds
Between 50 to 120 pounds