**When a fluid is moving, it moves such like that its mass remains conserved.**

Let us take a stream through which fluid is flowing. According to continuity equation, mass flow rate remains constant

For section A-A’ mass is given by

Similarly for Section B-B’

By contunity equation mass flow rate at both sections should be same, so

**Contunity Equation in 3D**

Contunity eqaution will be

If flow is steady, ∂ρ/∂t = 0

(always remember for steady state ∂/∂t = 0)

Contunity Equation becomes:

If fluid is incompressible then ρ = constant

contunity equation will become

Above equations can be modified according to the conditions given to us in our problems.

**Velocity of fluid particle**

##### Let Vr is the resultant velocity of any particle in ant flow. Let u,v,w be the velocity components in x,y,z direction respectively. Then resultant velociy will be

**Acceleration of fluid particle**

Let ax,ay,az are the acceleration in x,y,z, directions respectively