# Homework Help: Incompressible viscous liquid questions

1. Dec 22, 2008

### atavistic

Which of the following is true in a streamlined flow of incompressible viscous liquid?
A) When a fluid is in streamlined flow then there is transport of energy from one layer to another.
B) The speed of flow at all points in space is necessarily same.
C) The velocity of the liquid in contact with the containing vessel is zero.
D) None of the above.

I dont think this a homework type problem rather conceptual. Can somebody plz explain.

2. Dec 22, 2008

### Stovebolt

Re: Streamlined

You're right, this is a problem based more on the concept than any equations.

Have you seen a demonstration of streamlines? If so, visualizing that will probably help.

Think about each statement and whether it makes sense.

A) Each streamline represents a layer. Do the streamlines (layers) intersect?
B) If the streamlines encounter an object or the side of a containing vessel, can they speed up or slow down? It may help to think of air rushing by an airplane wing or along a rough surface.
C) This one might be a little more difficult to visualize. Think about how fast you can pour a viscous fluid like honey out of a jar and how fast it flows along the side of the jar compared to in the middle (this visualization may also help with part B)

Think about each one, and if any do or don't make sense.

3. Dec 22, 2008

### atavistic

Re: Streamlined

That was very nice reply Stovebolt.Thank You.

A) Streamlines don't intersect but does that mean they don't interact energetically?

B)I think they can speed up or slow down because if we take a crossection of the vessel then the volume of fluid it contains must pass through some other crossection and if I keep a big boulder in that crossectional volume , then the fluid will have to speed up.

C)The fluid in contact is slower but maybe because of surface tension.

4. Dec 23, 2008

### Stovebolt

Re: Streamlined

This depends on how you look at it. From a more simplistic viewpoint, there is almost no kinetic energy transfer, which I'm guessing is the "right" answer for this question.

However, if there's an energy differential, there's going to be energy transfer (e.g., if one stream is moving faster than another, and they are in contact, there will be some friction between them, meaning energy will be moving from one layer to the other)

Absolutely correct.

You're on the right track, though it isn't technically surface tension. There is a boundary layer between flowing fluid and a containing vessel. In this boundary layer, there are a number of forces that may be acting on the fluid - friction, drag, adhesion, etc, which act as a sheer force on the fluid. Since fluids have low resistance to sheer forces (depending on viscosity), these forces create an effective velocity of the fluid in contact with the vessel of zero.

I hope this helps. If you have any questions please let me know.