Physics XI Content
WORK
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PHYSICAL DEFINITION OF WORK | |||
“Work is said to be done if a force causes a displacement in a body in the direction of force”. OR “The work done by a constant force is defined as the product of the component of the force and the displacement in the direction of displacement.” | |||
MATHEMATICAL DEFINITION | |||
“Work is the scalar product of force and displacement”. OR “Work is the dot product of force and displacement”. | |||
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UNIT OF WORKS | |||
| • In S.I system: Joule (j) • In C.G.S. system: Erg • In F.P.S. system: ft X lb | |||
CATEGORIES OF WORK | |||
| (i) POSITIVE WORK: | |||
| If force and displacement are in the same direction, work will be positive or if q = 0 orq< 90° | |||
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| (ii) ZERO WORK: | |||
| If force and displacement are perpendicular to each other, work will be zero. i.e. | |||
since q = 90° Work = 0 as Work = Fd Cos q Work = Fd Cos 90° Work = (F)(d)(0) Work = 0 | |||
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| NEGATIVE WORK: | |||
| In force and displacement are in the opposite direction, work will be negative. | |||
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Since q = 180° Work = – ve as Work = Fd Cos q Work = Fd Cos 180° Work = (F)(d)(-1) Work = -Fd | |||