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# How does the viscosity of a liquid affect the flow of a sphere through it?

Extracts from this document...

Introduction

How does the viscosity of a liquid affect the flow of a sphere through it?

The resistance offered by a liquid/fluid (gases and liquids) on a moving object inside it is called viscosity. The flow of liquid occurs as the movement of layers at different speeds which in turn lead to a gradient of speeds and friction among them respectively.

Stokes’ Law

The viscous force offered by a fluid on a ball is directly proportional to the radius of the ball and its speed at a given instant.

F is proportional to r

F is proportional to v

F is proportional to rv

K=6πч

Ч= coefficient of viscosity

F= 6 π ч r v

F=Frictional Force

Ч= coefficient of viscosity

V=Velocity of the Sphere

Ч =F/6πrv = N/mms-1 =Nm-2s =Pa s

I believe that the density of the liquid will be directly proportional to the time taken for the sphere to drop.

Viscosity of various fluids

 Fluid Viscosity (Pa s) Hydrogen 8.4x10-6 Air 17.4x10-6 Xenon 2.12x10-5 (Room temperature) Blood 3x10-3 Castor oil 0.985 Glycerol 1.5 Mercury 1.5x10-3 Water 8.94x10-4

Up thrust (U)

Middle

Time 1 (Sec)

Time 2 (Sec)

Time 3 (Sec)

Average Time (Sec)

10

20

Total

500

0.97

44s

104s

146s

44s

105s

145s

45s

102s

146s

145.6s

10

20

Total

510

0.95

18

39

66

18

40

67

17

38

66

66.3s

10

20

Total

520

0.94

13

35

58

12

35

1.00

14

33

58

58.6s

10

20

Total

530

0.93

6

16

24

7

17

24

8

16

24

24.0s

10

20

Total

540

0.91

4

10

15

5

11

15

4

9

14

14.6s

10

20

Conclusion

For the second experiment the graph is quite different. This shows that as Density increases, time actually decreases. So the two quantities are inversely related. There is a constant pattern at first, but then due to human and systematic error there are a few anomalies.

Evaluation/Conclusion

You can see from the first graph that density and time are directly proportional, so as one goes up so does the other. This shows that the relationship between density and time is valid.

For the second graph, the two quantities are inversely related. This is because for that one the liquid is getting more viscous, so slowing down the sphere.

To improve the experiment I could take better precautions to reduce the errors, especially the human errors as they can be prevented more easily.

I could have tried to find out my reaction time and eliminate that from the time to make it more accurate.

Some of the limitations are that you can’t use very big objects, because they won’t fit through the cylinder, and also different shapes, because they have sides of different areas.

This student written piece of work is one of many that can be found in our GCSE Forces and Motion section.

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