# Help With Viscosity!!Watch

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#1
We did an experiment to calculate the viscosity of washing up liquid by dropping a small sphere through it.

The ball has a radius of 0.008m, mass 0.0058kg. It travelled 0.073m for 2.13s
We used 800cm^3 of liquid that had a mass of 0.824kg

Drag =6(Pi)nrv where n=coefficient of viscosity, r=radius(0.008m), v=velocity
n = Drag/6(Pi)rv

upthrust + viscous Drag = weight
drag = weight - upthrust
upthrust = 4Pi/3 x r^3 x fluid density x accelaration due to gravity

fluid density = 0.824kg / 0.008m^3 = 1030kgm^-3

n = (weight - upthrust)/6(Pi)rv

n=

(0.824kg x 9.81ms^-2) - (4(Pi)/3 x 0.008^3 x 1030 x 9.81)
------------------------------------------------------------------------------------- (division line)
6(Pi) x 0.008m x (0.073m/2.13s)

answer is something like 1571 Pa s which is way too high for a coefficient of viscosity

Please read through and give some help I have no idea where I have gone wrong
0
4 years ago
#2
(Original post by andyman1006)
We did an experiment to calculate the viscosity of washing up liquid by dropping a small sphere through it.

The ball has a radius of 0.008m, mass 0.0058kg. It travelled 0.073m for 2.13s
We used 800cm^3 of liquid that had a mass of 0.824kg

Drag =6(Pi)nrv where n=coefficient of viscosity, r=radius(0.008m), v=velocity
n = Drag/6(Pi)rv

upthrust + viscous Drag = weight
drag = weight - upthrust
upthrust = 4Pi/3 x r^3 x fluid density x accelaration due to gravity

fluid density = 0.824kg / 0.008m^3 = 1030kgm^-3

n = (weight - upthrust)/6(Pi)rv

n=

(0.824kg x 9.81ms^-2) - (4(Pi)/3 x 0.008^3 x 1030 x 9.81)
------------------------------------------------------------------------------------- (division line)
6(Pi) x 0.008m x (0.073m/2.13s)

answer is something like 1571 Pa s which is way too high for a coefficient of viscosity

Please read through and give some help I have no idea where I have gone wrong
Is that really the mass of the object you want to be calculating the weight force on?
0
1 month ago
#3
(Original post by andyman1006)
We did an experiment to calculate the viscosity of washing up liquid by dropping a small sphere through it.

The ball has a radius of 0.008m, mass 0.0058kg. It travelled 0.073m for 2.13s
We used 800cm^3 of liquid that had a mass of 0.824kg

Drag =6(Pi)nrv where n=coefficient of viscosity, r=radius(0.008m), v=velocity
n = Drag/6(Pi)rv

upthrust + viscous Drag = weight
drag = weight - upthrust
upthrust = 4Pi/3 x r^3 x fluid density x accelaration due to gravity

fluid density = 0.824kg / 0.008m^3 = 1030kgm^-3

n = (weight - upthrust)/6(Pi)rv

n=

(0.824kg x 9.81ms^-2) - (4(Pi)/3 x 0.008^3 x 1030 x 9.81)
------------------------------------------------------------------------------------- (division line)
6(Pi) x 0.008m x (0.073m/2.13s)

answer is something like 1571 Pa s which is way too high for a coefficient of viscosity

Please read through and give some help I have no idea where I have gone wrong
What you need to do is find the velocity the ball travelled at through the liquid (distance/time).
You also need to find the buoyancy (rho x g x v) of the liquid using it's density (mass/volume), gravity and the volume of the ball (4/3 x pi x radius^3)

Then you use the stokes law thingy
(Marble weight - buoyancy)/6pi x radius x velocity
In one formula that would be
((0.0058 x 9.81)-(4/3 pi x 0.008^3 x 1030 x 9.81))/6pi x 0.008 x (0.073/2.13) = 6.816
0
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