Tuesday 13 September 2011

WORK


In our daily life, the word work is used in connection with widely different activities. For example, we go to college; we study in the library; we play cricket. In physics, however, the term work is used in a restricted and well-defined manner. Work is said to be done when a force acts upon acts upon a body and produces a displacement.
DEFINITION: -
"The work done by a force in displacing an object is defined as the product of the distance and the component of the force in the direction of the distance".
If the angle between the distance S and the force F then the work done of that body is W = F. S Or W = FS Cos q
Work has no direction and is a scalar quantity. It is obvious form the above equation that work is the scalar product of force and distance. The work can be positive negative or zero. This is the essential way in which work defined in physics differs from the every day definition of work. The following special cases illustrate the difference among the various situations.
(i)                  The work done by a force is positive if the force has nonzero component in the same direction as the distance. i.e. the angle q between F and S is between 0 and 90 degree.
(ii)                The work by a force is negative if the force has nonzero component in direction opposite to the displacement, i.e. the angle q between F and S is between 90 and 180 degree so therefore Cosq is negative.
(iii)               No work is done by an external force F acting on a body if either the displacement S = 0 or if the displacement is perpendicular to F so that q is ± 90 degree and Cos q = 0 degree.
Similarly when a man walks at a constant velocity carrying a pail of water, he does no work on the pail, since the force F he exerts on the pail and the distance S are mutually perpendicular. Although the man holding the pail or carrying it horizontally does no work on it, the muscles in his arm do stretch and contract and thus some work is done internally, which may result in fatigue. But internal work, in physics, is not considered as work.
UNITS OF WORK: - In SI system the unit of work is JOULE and it is defined as,
“One Newton force is applied on a body and body moves through distance of 1 meter then total work is 1 joule”

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