# Mass and flow rate

1. May 7, 2010

### diagopod

Trying to understand the basics of fluid dynamics after reading up on Bernoulli's principle. One thing I'm caught on. If I know the velocity of an incompressible fluid at a given point, and the force it exerts on a given mass at that point, can I then determine the density of the fluid, or would I need more information? Conversely, if I know the density of the fluid, and the velocity, can then I then determine the force it will exert on a given mass in its path? Thanks for any guidance on this.

2. May 8, 2010

### tiny-tim

Hi diagopod!

If it's incompressible, then the density is constant.

You need to know the density to relate the speed to the pressure.

If you know the speed at two points along the same streamline, and the pressure at those two points, then Bernoulli's equation tells you that (in the absence of other influences such as gravity) density = 2 ∆(pressure)/∆(speed2).

3. May 8, 2010

### diagopod

Thanks tiny-tim, appreciate it.