# Chapter Two – Vectors and Equilibrium

Main focus of this chapter is to understand basic concepts of vectors, its components, vector algebra and equilibrium.

A physical quantity that requires only magnitude is known as scalar quantity whereas a physical quantity that needs both magnitude and direction is called vector.

When two or more vectors are added, we get a single vector (whose effect is same as the original vectors taken together) known as resultant vector. Vector addition is done by head to tail rule, according to which the sum of two vectors can be obtained by joining the tail of first vector to the head of second vector. To represent the direction of a vector in space unit vector is used. Magnitude of a unit vector is one.A vector whose magnitude is zero without any specified direction is null vector. vector is used to describe the location of a particle with respect to origin position.

The scalar or dot product of two vectors is a scalar quantity, and the vector or cross product of two vectors is a vector.

The product of force and moment arm is torque.

If there is no resultant force or resultant torque, system is in equilibrium.