Measuring Viscosity (Viscometer)

[Hornet-Wing]

Hi, even though this is my first post, Physics Forums have helped my a over that past couple of years. Just searching old PF threads usually gave me the answer I was looking for. So thanks.

I am currently doing Advanced Higher (Scottish Qualification) Physics Investigation on Viscosity. During my investigation I would like to complete about 3 experiments and compare the results for accuracy. I have come up with one experiment:

Dropping a ball through the liquid:

Brief Summary:
Drop a ball through liquid and find its terminal velocity with the use of a camcorder and a picket fence. Then work out its viscosity using Stokes' Law.

Are there any other experiments that I could use in my investigation? They do not have to be 100% accurate (only 99.999% ) but they can't be apparatus intensive.

Thanks Very Much for reading!

EXP1:
http://www.aerohornet.com/files/exp1.jpg

 

[arildno]

Two other experiments you might try out is:
a) Drag a plate at known velocity V on top of the fluid layer. You should be able to figure out the viscosity from the force you need to drag the plate along with constant velocity.

b) Have the fluid in a cylinder which you rotate at a given angular velocity.
You could figure out the viscosity from the applied torque.

 

[Hornet-Wing]

That was fast

Do you have any equations for the methods mentioned?

 

[Dadface]

Hello Hornet wing look up Poiseieuilles formula and method.You can easily knock the apparatus together using standard bits of laboratory equipment.Some of the older A level texts such as Nelkon and Parker give good accounts of the method and I also suggest that you search for some of the older A level practical guides.

 

[arildno]

That was fast

Do you have any equations for the methods mentioned?

Sure, but you should try to set them up by yourself first.

 

[Dadface]

Does your school/college have an Ostwald viscometer?

 

[Hornet-Wing]

I have had a look at Poiseuille’s method and it definitely looks like one I would do and Ill look out for Nelkon and Parker's book. So that's 2 possible methods, 1 or 2 methods still to be found.

@arildno, that's a good point, finding out myself will probably keep me more interested. Both methods look interesting to do especially as we just covered torque and angular velocity this year.

@Dadface, Ill need to find out of they have one, but I doubt it. The school is now over 100 years old and so is most of the equipment . However that could be my 3rd method.

 

[arildno]

Make it simple for yourself at first!

For example, in the case of the flat plate, consider a horizontal bottom and ignore the "edge effects" of the plate, i.e, regard it as infinite of relevant lengths.

You should get a velocity distribution that varies linearly with the depth.

 

[skeleton]

Two other experiments you might try out is:

b) Have the fluid in a cylinder which you rotate at a given angular velocity.
You could figure out the viscosity from the applied torque.

I like this one. One could establish an easy made torque device:

APPARATUS
- Make a circular paddle wheel, with a vertical spindle above it.
- Wrap string around the spindle and have it extend away.
- The free end of the string passes over a pulley, which directs it downwards.
- Attach a known mass at the free end of the string. Gravity will pull on the mass with a known force.

CALIBRATION
- Some energy is lost through the spindle rotation and the pulley. This can be estimated if considered significant for your accuracy.
- Do a "dry run", where there is no liquid in the viscosity tank - just air. Turn the paddles 90 degrees so they "cut" into the wind, to reduce air drag.
- Now, run and time the apparatus.
- Theory of kinematics can predict the rate of acceleration of the rotating paddle in a vacuum (close enough). The difference observed indicates the energy lost.

 

[Hornet-Wing]

Thank You Very Much!

I asked my teacher about the 2 methods mentioned by arildno and although he had heard of them he wasn't sure what the equations were of how it worked.