Stoke's Law - Method and how to do it - graph?

In summary, Stoke's law can be calculated using a gradient equation. When calculating the coefficient of viscosity, use the equation k = Vs.
  • #1
zkm1223
3
0
Stoke's Law - Method and how to do it - graph?

Homework Statement


Hi, i have to write a method to do stoke's law on different ball bearings and draw a graph of stoke's law of different ball bearings in glycerol and from the graph i have to find the viscosity of the liquid. How do i do this?


Homework Equations


I have the top 2 formula's from:
http://en.wikipedia.org/wiki/Stokes'_law


The Attempt at a Solution


Don't know where to start, so please help. thanks in advance.
 
Physics news on Phys.org
  • #2


Find radii of different balls. Find their terminal velocities. Draw a graph of R^2 vs terminal . It will be a straight line. From the Slop of this line can find the coefficient of viscosity.
 
  • #3


thanks for your reply. so i measure the diameter using a micrometer, then halve to get radius. but how do i find terminal velocity and is the viscosity the gradient of the line? will it be the same for all ball bearings? also what are the formulas for?
 
  • #4


The terminal velocity will be different for different balls.
Take a glass tube of 5 cm diameter. Fill it with glycerol. From liquid level make 5 cm marks on the tube.
Drop a ball bearing. Start the stop watch when the ball enters the liquid. Note down the time whenever the ball crosses the 5 cm mark. When the time interval (t) becomes constant, the terminal velocity will be 5cm/t. Find the densities of the ball and liquid by any method. Using second formula find coefficient o viscosity. of glycerol.
 
  • #5


rl.bhat said:
Find radii of different balls. Find their terminal velocities. Draw a graph of R^2 vs terminal . It will be a straight line. From the Slop of this line can find the coefficient of viscosity.

I think you draw terminal vs r^2 i.e terminal on the y-axis and radii on x axis?
 
  • #6


Yes. Slope of the graph m = 2/9*[rho(b) - rho(gl)]*g/mu, where mu is coefficient of viscosity. From this you can find mu.
 
  • #7


rl.bhat said:
Yes. Slope of the graph m = 2/9*[rho(b) - rho(gl)]*g/mu, where mu is coefficient of viscosity. From this you can find mu.

The problem i have with this is that once one has found the gradient of the graph and thus deciphered the value of the constant k, which value would one use for the density of sphere as they all vary
 
  • #8


quinox3o0o said:
The problem i have with this is that once one has found the gradient of the graph and thus deciphered the value of the constant k, which value would one use for the density of sphere as they all vary
If the material of the ball bearings is same, then the density of them will also be the same.
 
  • #9


I get that k is the gradient, however this doesn't make sense to me:
where mu is coefficient of viscosity. From this you can find mu.

Can you explain further please?
 
  • #10


rl.bhat said:
If the material of the ball bearings is same, then the density of them will also be the same.

ahh i realized after i posted the question how stupid i was, ofc the density doesn't change its the same material !

citizensparks said:
I get that k is the gradient, however this doesn't make sense to me:


Can you explain further please?

when you found k, use this equation http://upload.wikimedia.org/math/3/d/b/3dbef61d20c1951c09a727ff8d4a809c.png, where k is equal to Vs to find the value of u which will be the viscosity of the material
 
  • #11


when you found k, use this equation http://upload.wikimedia.org/math/3/d...ff8d4a809c.png , where k is equal to Vs to find the value of u which will be the viscosity of the material
But aren't we looking for the coefficient of viscosity, not viscosity itself? Because the experiment is investigating stokes law, which is F = 6 x Pi x r x coefficient of viscosity x v.

If k = viscosity, we aren't finding the coefficient. Or am I just getting really confused and over complicating it? (I have a feeling I am).
 
Last edited by a moderator:
  • #12


dfgdfg
 
Last edited:
  • #13


quinox3o0o said:
sorry let me start again, the value of the gradiet is equal to the value of Vs in the equation, http://upload.wikimedia.org/math/3/d/b/3dbef61d20c1951c09a727ff8d4a809c.png, the letter U represents coefficient of viscosity, so rearrangement and you have your answer.
Btw are you doing this for some sort of cw?

Ok, that makes more sense; thanks. And yes I am. I'll use this thread as a source for calculating and describing the graph, shouldn't be a problem.
 

FAQ: Stoke's Law - Method and how to do it - graph?

1. What is Stoke's Law and how does it work?

Stoke's Law is a mathematical equation that describes the settling velocity of a spherical particle in a viscous fluid. It states that the settling velocity is directly proportional to the particle's radius, the density difference between the particle and the fluid, and the gravitational acceleration. It is commonly used in sedimentation experiments to determine the size and density of particles in a fluid.

2. What materials are needed to perform a Stoke's Law experiment?

To perform a Stoke's Law experiment, you will need a container or tube filled with a viscous fluid (such as water or oil), a spherical particle of known size and density, a stopwatch, and a ruler or measuring device to record the settling distance of the particle.

3. How do you calculate the settling velocity using Stoke's Law?

The settling velocity can be calculated using the equation v = (2/9) * (d^2) * (p_p - p_f) * g / u, where v is the settling velocity, d is the particle's diameter, p_p is the particle's density, p_f is the fluid's density, g is the gravitational acceleration, and u is the fluid's viscosity. You can also use a Stoke's Law calculator or a graph to determine the settling velocity.

4. How do you create a graph for a Stoke's Law experiment?

To create a graph for a Stoke's Law experiment, plot the settling velocity (y-axis) against the particle diameter (x-axis). The data points should follow a linear trend, and the slope of the line can be used to calculate the viscosity of the fluid. You can also plot the settling velocity against the particle density or density difference to determine the relationship between these variables.

5. What are some sources of error in a Stoke's Law experiment?

Some sources of error in a Stoke's Law experiment include human error in measuring the settling distance or timing, variations in the fluid's temperature or viscosity, and irregularities in the particle's shape or density. It is important to repeat the experiment multiple times and take an average to reduce these sources of error.

Similar threads

Solving Distance of Starch Particles in Fluid w/Stoke's Law
Replies
2
Views
1K
Viscosity by Falling Sphere Equations
Replies
2
Views
800
Viscosity and temperature, density is changing....
Replies
29
Views
4K
Linearising an Inverse Square Law Graph for Gamma Radiation
Replies
5
Views
4K
B Log relationship between thickness of material and sound absorbed?
Replies
1
Views
610
Coursework help - Stokes Law equation + graphs
Replies
4
Views
4K
How Do Stokes Parameters Relate to Polarized Light Components?
Replies
1
Views
1K
Understanding the math of definition of electromotive force
Replies
1
Views
491
Stokes Law/Drag Force corrections?
Replies
1
Views
4K
GR- Energy conservation, effective potential graph sketch
Replies
1
Views
1K

Hot Threads

Recent Insights

Back
Top