EXPERIMENT NO.10
VISCOSITY OF A LIQUID
Objective
To determine the coefficient of viscosity of a given viscous liquid by measuring terminal velocity of a
given spherical body.
Theory
Viscosity is the property of a fluid by virtue of which an internal resistance comes into play when the
liquid is in motion and opposes the relative motion between its different layers. Thus, it is the resistance
of a fluid to flow.
When liquid flows over flat surface, a backward viscous force acts tangentially to every layer. This force
depends upon the area of the layer, velocity of the layer, and the distance of the layer from the surface.
Where η is the coefficient of viscosity of the liquid.
Stoke’s Law
Stoke’s law was established by an English scientist Sir George G Stokes (1819-1903).
When a spherical body moves down through an infinite column of highly viscous liquid, it drags the layer
of the liquid in contact with it. As a result, the body experiences a retarding force.
Then according to Stokes law, the viscous drag force,
Where, r - Radius of the spherical body
v - Velocity of the spherical body
It gives the relationship between retarding force and velocity. When viscous force plus buoyant force
becomes equal to force due to gravity, the net force becomes zero. The sphere then descends with a
constant terminal velocity (v).
Now,
Where, ρ - Density of the liquid
, σ - Density of the spherical body
Procedure
1. Access the simulation package thru http://amrita.olabs.edu.in/?sub=1&brch=5&sim=225&cnt=4
2. Study the controls of the simulation package.
3. Select earth ( g =9.8m/s2) from the “ Select the Environment drop down list.
4. Select the liquid for which the coefficient of viscosity is to be measured, from the 'Select Viscous
Liquid' drop down list.
5. Use the ‘Select jar diameter’ slider to change the diameter of the glass jar.
6. Use the ‘Select ball diameter’ slider to change the diameter of the glass ball.
7. Change the distance between A and B by dragging the corresponding arrows.
8. Drag the glass ball towards the jar and drop it into the liquid in the jar.
9. The stopwatch runs automatically as the ball reaches the point A, and stops as it leaves the point B.
10. The time shown in the stopwatch is noted.
11. The velocity of the ball can be obtained using:
Where, d = distance between point A and B = 60.0cm
12. Calculate the terminal velocity of the ball using the equation
Where, r = radius of the ball
R = radius of the jar
13. Now, calculations are done as per the observation column and the coefficient of viscosity of the
selected liquid can be found out.
14. Enable the ‘Show result’ checkbox to view the coefficient of viscosity (simulation) of the selected
liquid.
VISCOSITY OF A LIQUID
Objective
To determine the coefficient of viscosity of a given viscous liquid by measuring terminal velocity of a
given spherical body.
Theory
Viscosity is the property of a fluid by virtue of which an internal resistance comes into play when the
liquid is in motion and opposes the relative motion between its different layers. Thus, it is the resistance
of a fluid to flow.
When liquid flows over flat surface, a backward viscous force acts tangentially to every layer. This force
depends upon the area of the layer, velocity of the layer, and the distance of the layer from the surface.
Where η is the coefficient of viscosity of the liquid.
Stoke’s Law
Stoke’s law was established by an English scientist Sir George G Stokes (1819-1903).
When a spherical body moves down through an infinite column of highly viscous liquid, it drags the layer
of the liquid in contact with it. As a result, the body experiences a retarding force.
Then according to Stokes law, the viscous drag force,
Where, r - Radius of the spherical body
v - Velocity of the spherical body
It gives the relationship between retarding force and velocity. When viscous force plus buoyant force
becomes equal to force due to gravity, the net force becomes zero. The sphere then descends with a
constant terminal velocity (v).
Now,
Where, ρ - Density of the liquid
, σ - Density of the spherical body
Procedure
1. Access the simulation package thru http://amrita.olabs.edu.in/?sub=1&brch=5&sim=225&cnt=4
2. Study the controls of the simulation package.
3. Select earth ( g =9.8m/s2) from the “ Select the Environment drop down list.
4. Select the liquid for which the coefficient of viscosity is to be measured, from the 'Select Viscous
Liquid' drop down list.
5. Use the ‘Select jar diameter’ slider to change the diameter of the glass jar.
6. Use the ‘Select ball diameter’ slider to change the diameter of the glass ball.
7. Change the distance between A and B by dragging the corresponding arrows.
8. Drag the glass ball towards the jar and drop it into the liquid in the jar.
9. The stopwatch runs automatically as the ball reaches the point A, and stops as it leaves the point B.
10. The time shown in the stopwatch is noted.
11. The velocity of the ball can be obtained using:
Where, d = distance between point A and B = 60.0cm
12. Calculate the terminal velocity of the ball using the equation
Where, r = radius of the ball
R = radius of the jar
13. Now, calculations are done as per the observation column and the coefficient of viscosity of the
selected liquid can be found out.
14. Enable the ‘Show result’ checkbox to view the coefficient of viscosity (simulation) of the selected
liquid.
