# Does viscosity have to do with density?

1. Jun 24, 2015

### Alex299792458

When you look at a viscous fluid its so thick and it seams that its dense and a runny fluid seams less dense. Like if you take a bottle of syrup it fells a bit heavier than a bottle of water. Plus if the atom are packed closer to each other (and in the form of liquid the atoms move past each other thats why they can take the shape of the container) they will crash in to each other and make friction slowing them down in a thick viscous fluid , right? I dont know if any of that is true so tell if I'm and is viscosity is caused by density.

2. Jun 24, 2015

### gleem

I am not an expert in this area but I believe viscosity is primarily due to inter molecular forces. Some examples that refute your observations are motor oil which is very viscous but less dense that water and mercury which is not viscous in the usual sense but very dense.

3. Jun 24, 2015

### davenn

excellent response gleem

4. Jun 27, 2015

### stedwards

If idioms serve any weight, molasses is slower in January than July. The viscosity of molasses would seem to rely more strongly on temperature than density.

5. Jun 27, 2015

### phinds

agreed

6. Jun 27, 2015

### phinds

Good point.

7. Jun 27, 2015

### Staff: Mentor

Motor oil is more viscous than water, but is also less dense - it floats.
So I don't think that the hypothesis that viscosity is caused by density is going to work.

8. Jun 27, 2015

### phinds

You must have missed post #2

9. Jun 27, 2015

### FL0R1

Viscosity its related to density so yes they do have a relationship between each other, the fludid have their own viscosity and their own density.. thnx

10. Jun 27, 2015

Staff Emeritus
That makes no sense. That's like saying countries have their own populations and letters in their names, so there is a relationship between them.

11. Jun 27, 2015

### phinds

Have you not been reading this thread? After what's been posted, you're going to have to be a lot more specific and convincing than to simply state something that defies what has already been said.

12. Jun 27, 2015

### stedwards

I couldn't decode his post, but it would be shocking know there were no dependent of viscosity on pressure for any given fluid, other than a superfluid.

However, it's seems fairly true for nearly all fluids, that for any given temperature, where the pressure ranges from evaporation to solidification, $\Delta \mu / \Delta P$, is much less than one:

The change in viscosity over the change in pressure is small in most, if not, all common fluids, is small.​

And I think there is a predatory tendency, sadists with various titles, on this web site that relish in beating-up on anyone including children, and that really bothers me . What do you think?

Last edited: Jun 27, 2015
13. Jun 27, 2015

### phinds

Which of posts 2, 4, and 7 could you not decode?

Uh, when did pressure get brought in, other than by you just now and not in your post to which I reponded?

I didn't know we had any children on the forum and I think you are being overly sensitive to criticism. The forum is about science and facts, not about beating anyone up.

14. Jun 27, 2015

### stedwards

You can be adversarial-lite at times, phinds. I've read many of your posts. Of course there are children.

Last edited: Jun 27, 2015
15. Jun 27, 2015