Question

what is velocity and density

Answer 1

Mass Flow Rate is defined as the transfer of a mass of substance per unit of time. Mass flow rate can be calculated from the density of the liquid (or gas), its velocity, and the cross sectional area of flow. This advanced online Mass Flow Rate Calculation tool is used to calculate the Mass Flow Rate of liquid or gas.

Answer 2

velocity is the rate of change of displacement.
density is the ratio of mass and volume