Work
The concept of work is important to scientists and engineers for
determining the energy needed to perform various jobs. For instance, it
is useful to know the amount of work done when a crane lifts a steel
girder, when a spring is compressed, when a rocket is propelled into the
air, or when a truck pulls a load along a highway.
In general, work is done by a force when it moves an object. If the force
applied to the object is constant, then the definition of work is as
follows:
DEFINITION OF WORK DONE BY A CONSTANT FORCE
If an object is moved a distance D in the direction of an applied constant
force F, then the work W done by the force is defined as W = FD.
There are many types of forces – centrifugal, electromotive, and
gravitational, to name a few. A force can be thought of as a push or pull;
a force changes the state of rest or state of motion of a body. For
gravitational forces on Earth, it is common to use units of measure
corresponding to the weight of an object.
Example 1. Lifting an Object
1. Determine the work done in lifting a 50-pound object 4 feet.
W = FD
= 50 (4)
W = 200 foot – pounds
In the US Measurement system, work is typically expressed in foot-
pounds (ft – lb), inch – pounds, or foot – tons. In the centimeter – gram
– second (C-G-S) system, the basic unit of force is dyne- the force
required to produce an acceleration of 1 centimeter per second per
second on a mass of 1 gram. In this system, work is typically expressed
