Viscosity by Falling Sphere Equations

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An experiment was conducted to measure the viscosity of water using the falling sphere method with spheres of varying diameters (2.5 to 20 mm). The aim was to demonstrate that sphere diameter does not affect liquid viscosity, but the calculated viscosity was significantly higher than the expected 0.001 Pas, reaching around 0.84 Pas. This discrepancy raised questions about the influence of sphere diameter on viscosity and terminal velocity. Participants discussed the relevance of Stokes' law, emphasizing that it applies under laminar flow conditions and may not hold true at higher Reynolds numbers. Clarification on measurement values and conditions was requested to further analyze the results.
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Homework Statement
I have recently conducted an experiment to measure the viscosity of some liquids using the falling sphere method and a high-speed camera. I used different diameters of sphere starting from 2.5, 5, 10, 15 and 20 mm. What I want to prove using stokes law equation is that diameter of sphere doesn't affect viscosity of a liquid and it will stay the same. I guess it's okay if it has a little bit different viscosity for each diameter, however when I calculate using the stokes law formula, the difference is so big and when I compared it to the real viscosity of the liquid it's also so different. The liquid is water, which was supposed to have 0.001 Pas, but my calculated value is around 0.84 Pas. I need help, does diameter affect viscosity? if I'm not wrong it only affects the terminal velocity. How please??
Relevant Equations
η = 2gr^2(d'– d)/9v
where:
v is the particles' terminal velocity velocity (m/s),
r is the radius of the sphere,
g is the gravitational acceleration,
d' is the density of the falling sphere,
d is the density of the liquid,
and η is the viscosity.
I have recently conducted an experiment to measure the viscosity of some liquids using the falling sphere method and a high-speed camera. I used different diameters of sphere starting from 2.5, 5, 10, 15 and 20 mm. What I want to prove using stokes law equation is that diameter of sphere doesn't affect viscosity of a liquid and it will stay the same. I guess it's okay if it has a little bit different viscosity for each diameter, however when I calculate using the stokes law formula, the difference is so big and when I compared it to the real viscosity of the liquid it's also so different. The liquid is water, which was supposed to have 0.001 Pas, but my calculated value is around 0.84 Pas. I need help, does diameter affect viscosity? if I'm not wrong it only affects the terminal velocity. How please??
 
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xenoidmaster said:
Homework Statement: I have recently conducted an experiment to measure the viscosity of some liquids using the falling sphere method and a high-speed camera. I used different diameters of sphere starting from 2.5, 5, 10, 15 and 20 mm. What I want to prove using stokes law equation is that diameter of sphere doesn't affect viscosity of a liquid and it will stay the same. I guess it's okay if it has a little bit different viscosity for each diameter, however when I calculate using the stokes law formula, the difference is so big and when I compared it to the real viscosity of the liquid it's also so different. The liquid is water, which was supposed to have 0.001 Pas, but my calculated value is around 0.84 Pas. I need help, does diameter affect viscosity? if I'm not wrong it only affects the terminal velocity. How please??
Relevant Equations: η = 2gr^2(d'– d)/9v
where:
v is the particles' terminal velocity velocity (m/s),
r is the radius of the sphere,
g is the gravitational acceleration,
d' is the density of the falling sphere,
d is the density of the liquid,
and η is the viscosity.

I have recently conducted an experiment to measure the viscosity of some liquids using the falling sphere method and a high-speed camera. I used different diameters of sphere starting from 2.5, 5, 10, 15 and 20 mm. What I want to prove using stokes law equation is that diameter of sphere doesn't affect viscosity of a liquid and it will stay the same. I guess it's okay if it has a little bit different viscosity for each diameter, however when I calculate using the stokes law formula, the difference is so big and when I compared it to the real viscosity of the liquid it's also so different. The liquid is water, which was supposed to have 0.001 Pas, but my calculated value is around 0.84 Pas. I need help, does diameter affect viscosity? if I'm not wrong it only affects the terminal velocity. How please??
What's the Reynolds number for the sphere falling in water? Stokes law is valid for laminar flow.

i.e. Does the velocity of the sphere as it falls match expectations for the equation of motion:

$$ m\dot v = mg - \beta v $$

Where ##\beta## is approximately constant?
 
Just to check, please post one set of values of all the measurements, quoting units.
 
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