# Newtonian viscosity equaton

1. Jun 17, 2007

### black_kitty

Could anyone explain me and comment the Newtonian viscosity equaton?

2. Jun 17, 2007

### arildno

I assume you mean, why is the force of friction in a fluid proportional to the velocity gradient in it? (the proportionality factor being the viscosity)

The simplest answer is that meticulous experiments showed that that was, indeed, a very good approximation.

There's a lot more to say about this, of course, but I'll let this be enough for today