**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”.

Work is a scalar quantity.

**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**

**1. Positive work:**

If force and displacement are in the same direction, work will be positive or if q = 0 orq< 90°

**2. 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

**3. Negative work:**

In force and displacement are in the opposite direction, work will be negative.

Since q = 180°

Work = – ve

as

Work = Fd Cos q

Work = Fd Cos 180°

Work = (F)(d)(-1)

Work = -Fd

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