1. Resultant Vector

A resultant vector is a single vector that has the same effect as the combined effect of all the vectors to be added.

                                                  OR

The sum of two or more vectors is a single vector, which has the same effect as the combined effect of all the vectors to be added. This single vector is called the resultant vector.

2. Torque

The turning effect of a force is called torque or moment of the force.

$\tau=F\times L$

Torque is a vector quantity and its direction can be found by using the right and rule.

Unit of torque

The unit of torque is Nm

3. Centre of Mass

Centre of the mass of a system is such a point where an applied force causes the system to move without rotation.

4. Centre of Gravity

A point where the whole weight of the body appears to act vertically downward is called the Centre of gravity of a body.