# Kinetic energy of fluid + collision

1. Nov 27, 2015

### tonyjk

Hello,

When a fluid is flowing, it has of course a kinetic energy and thus we can define kinetic power equal to ρAv v is the velocity and A is the surface of a solid for example. I have a question (maybe it is a strange one) : When fluid collides with a solid, do all the molecules collide with the solid or some of them or we cannot know?

Thanks

2. Nov 27, 2015

Staff Emeritus
When you put a penny in a river, does ever molecule of water collide with the penny?

3. Nov 27, 2015

### tonyjk

I am talking about the quantity ρAv

4. Nov 28, 2015

Staff Emeritus
Which is not a volume.

5. Nov 28, 2015

### tonyjk

how it is the mass of the volume Av

6. Nov 28, 2015

Staff Emeritus
I don't understand that. It is not a sentence, and Av is neither a mass nor a volume.

7. Nov 28, 2015

### tonyjk

Velocity multiply by surface you will get m3/s so it is a volumetric flow rate. If you multiply by ρ(rho) we will get mass flow rate.

8. Nov 28, 2015