Mechanical
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Work
is done upon an object whenever a force acts upon it to cause
it to be displaced. Work is a force acting upon an object
to cause a displacement. In all instances in which work is
done, there is an object which supplies the force in order
to do the work. If a World Civilization book is lifted to
the top shelf of a student locker, then the student supplies
the force to do the work on the book. If a plow is displaced
across a field, then some form of farm equipment (usually
a tractor or a horse) supplies the force to do the work on
the plow. If a pitcher winds up and accelerates a baseball
towards home plate, then the pitcher supplies the force to
do the work on the baseball. If a roller coaster car is displaced
from ground level to the top of the first drop of the Shock
Wave, then a chain (driven by a motor) supplies the force
to do the work on the car. If a barbell is displaced from
ground level to a height above a weightlifter's head, then
the weightlifter is supplying a force to do work on the barbell.
In all instances, an object which possesses some form of energy
supplies the force to do the work. In the instances described
here, the objects doing the work (a student, a tractor, a
pitcher, a motor/chain) possess chemical potential energy
stored in food or fuel which is transformed into work. In
the process of doing work, the objects doing the work exchange
energy in one form to do work on another object to give it
energy. The energy acquired by the objects upon which work
is done is known as mechanical energy.
Mechanical energy is the energy which is
possessed by an object due to its motion or its stored energy
of position. Mechanical energy can be either kinetic energy
(energy of motion) or potential energy (stored energy of
position). Objects have mechanical energy if they are in
motion and/or if they are at some position relative to a
zero potential energy position (for example, a brick held
at a vertical position above the ground or zero height position).
A moving car possesses mechanical energy due to its motion
(kinetic energy). A moving baseball possesses mechanical
energy due to both its high speed (kinetic energy) and its
vertical position above the ground (gravitational potential
energy). A World Civilization book at rest on the top shelf
of a locker possesses mechanical energy due to its vertical
position above the ground (gravitational potential energy).
A barbell lifted high above a weightlifter's head possesses
mechanical energy due to its vertical position above the
ground (gravitational potential energy). A drawn bow possesses
mechanical energy due to its stretched position (elastic
potential energy).
An object which possesses mechanical energy
is able to do work. In fact, mechanical energy is often
defined as the ability to do work. Any object which possesses
mechanical energy - whether it be in the form of potential
energy or kinetic energy - is able to do work. That is,
its mechanical energy enables that object to apply a force
to another object in order to cause it to be displaced.
Numerous examples can be given of how an
object with mechanical energy can harness that energy in
order to apply a force to cause another object to be displaced.
A classic example involves the massive wrecking ball of
a demolition machine. The wrecking ball is a massive object
which is swung backwards to a high position and allowed
to swing forward into building structure or other object
in order to demolish it. Upon hitting the structure, the
wrecking ball applies a force to it in order to cause the
wall of the structure to be displaced.
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