I'm trying to figure out what the physical meaning of divergence is for a vector field. My textbook offered the following example: if v = <u, v, w> represents the velocity field of a fluid flow, then div(v) evaluated at P = (x, y, z) represents the net rate of the change of mass of the fluid flowing from the point P per unit volume. How is this possible? Velocity has units of [m/s]. Based on the definition of divergence, div(v) would have units of [m/s^2]. Where in the world do we get a unit of mass? I've been scouring the internet trying to find some clarification, but every source has been using either words like amount and volume interchangeably or talking about things like source/sink without clarifying what is meant. Any help would be much appreciated.