Page 89 - Schaum's Outline of Theory and Problems of Applied Physics
P. 89
CHAPTER 7
Energy
WORK
Work is a measure of the amount of change (in a general sense) that a force produces when it acts on a body. The
change may be in the velocity of the body, in its position, in its size or shape, and so forth.
By definition, the work done by a force acting on a body is equal to the product of the force and the distance
through which the force acts, provided that F and s are in the same direction. Thus
W = Fs
Work = (force)(distance)
Work is a scalar quantity; no direction is associated with it.
If F and s are not parallel but F is at the angle θ with respect to s, then
W = Fs cos θ
Since cos 0 = 1, this formula becomes W = Fs when F is parallel to s. When F is perpendicular to s, θ = 90 ◦
and cos 90 = 0. No work is done in this case (Fig. 7-1).
◦
The unit of work is the product of a force unit and a length unit. In SI units, the unit of work is the joule (J).
SI units : 1 joule (J) = 1 newton-meter = 0.738 ft·lb
British units : 1 foot-pound (ft·lb) = 1.36 J
Fig. 7-1
SOLVED PROBLEM 7.1
A horizontal force of 420 N is used to push a crate for 5 m across a level warehouse floor. How much
work is done?
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