# Fluid mechanics(viscosity)

1. Aug 29, 2009

### Godwin Kessy

Can any one help me define viscosity and the newtons relations to define viscosity
Surely am having a confusion as follows;
Does viscosity define how diffcult is it to move a layer of liquid relative to another!!
Or a Frictional force existing between layers in relative motion!!!!

This quetion arised due to the fact that;
F is directly proportinal to dv/dx!!

2. Aug 29, 2009

### kyiydnlm

yeah, you can say that.

3. Sep 2, 2009

### Godwin Kessy

But can't you really find a confusion on that!!
That, if friction force between layers is greater, that means dv/dx is less because there would exist larger frictional force to allow greater difference in velocity per change in vertical displacement!!(contrary to newton's relation that Frictional force is directly proportional to dv/dx

At the same time when dv/dx is greater there exist more frictional force between layers and that is why terminal velocity can be attained!! This goes in hand with the newton's relation.

4. Sep 2, 2009

### kyiydnlm

OK, you can think about it this way. If you put a box on a smooth surface and a same box on a rough surface. and you push them with same force, which one moves faster? or you try to keep them with same speed, which one needs larger force?

now, put two boxes on same surface, but one surface is covered with very thick oil, the other with thin oil. Look, you create fluid layers, one set with high viscosity, the other with low viscosity. they are simillar to boxes on solid surface.

but if you want to understant it more precisely, you have to take a look at its definition $$\tau=\mu\frac{dv}{dx}$$

5. Sep 19, 2009

### Godwin Kessy

[QUOTE
now, put two boxes on same surface, but one surface is covered with very thick oil, the other with thin oil. Look, you create fluid layers, one set with high viscosity, the other with low viscosity. they are simillar to boxes on solid surface.

but if you want to understant it more precisely, you have to take a look at its definition $$\tau=\mu\frac{dv}{dx}$$[/QUOTE]

you have spoke of same fluid and after the same time you speak of different viscosity
I don't really get you well?