Considering different positive and negative signs, the work du can be defined as-

- Angle will be acute for positive value of du
- Angle will be obtuse for negative value of du

Thus, three cases are formed for work calculation, i.e.

- When force F is in the direction of dr, the value of work du can be written as + F. ds
- When force F is in opposite direction of dr, the value of work du can be written as – F. ds
- When force F is perpendicular to dr, the value of work du can be written as 0 (zero)

**Links of Previous Main Topic:-**

- Introduction concept of equilibrium of rigid body
- Friction introduction
- Introduction about distributed forces
- Area moments of inertia in rectangular and polar coordinates
- Mass moment of inertia introduction
- Work done by force
- Sign convention of mechanical work

**Links of Next Mechanical Engineering Topics:-**