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Viscosity - Comparing the viscosities of different liquids.

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Introduction

Blerim Shahaj        -  -        Physics Course Work

Viscosity

Comparing the viscosities of different liquids.

Introduction and Hypotheses

If we move through a pool of water we experience a resistance to our motion. This shows that there is a frictional force in liquids. We say this is due to the viscosity of the liquid. The viscosity of a liquid is a measure of its resistance to flow and is caused by the internal friction of the liquid. If the frictional force is comparatively low as in water the viscosity of the liquid is low. If the frictional force is large, as in glue or glycerine, the viscosity of the liquid is high.  We can compare roughly the viscosity of two liquids by filling two measured cylinders with each of them, and allowing identical small steel ball bearings to fall through each liquid. The ball bearing falls slower through the liquid with higher viscosity.

I am going to investigate three different liquids and compare their viscosities. The liquids I am going to investigate are: oil, washing liquid and honey.

I predict that the viscosity of the honey will be the highest due to the fact that honey flows much slower than oil or washing liquid.

I predict that the upthrust force will be much bigger in honey due to higher density in honey. The upthrust force will be the lowest in oil since this has the lowest density of the three liquids under consideration.

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Middle

Average Time

0.2

27

24

24

25

0.2

28

26

26

26.67image02.png

0.2

29

28

33

30

0.2

37

32

43

37.33

0.2

50

48

50

49.33

0.2

57

55

53

55

0.2

58

56

54

56

Washing Liquid

Distance (m)

Time I (s)

Time II (s)

Time III (s)

Time IV (s)

Average Time

0.2

1.16

1.24

1.12

1.17

1.17

0.2

1.32

1.36

0.96

0.96

1.15

0.2

1.18

1.22

1.05

1.14

1.15

0.2

2.38

1.42

1.37

1.19

1.59

0.2

1.42

1.44

1.73

1.32

1.48

0.2

1.37

1.45

1.87

1.45

1.54

0.2

1.43

1.48

1.86

1.48

1.56

0.2

1.44

1.5

1.84

1.46

1.56

Note: The reading painted in red seems to stand out from the other readings image02.png

therefore it makes me believe its a wrong reading.

Oil

Distance (m)

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Conclusion

-2)

Honey

399.9

Washing liquid

11.5

Oil

3.11

As shown in the table above honey has the highest viscosity, it is in fact approximately 100 times more viscous than oil and about 40 times more viscous than washing liquid.

The table below shows the upthrust force acting on the ball bearing when immersed in each of the liquids

Liquid

Upthrust force (in N )

Honey

0.022

Washing liquid

0.017

Oil

0.014

The upthrust force is higher in honey, this is predictable since the density of honey is greater.

The table below shows the terminal speed values for the three liquids.

Liquid

Terminal speed

Honey

0.0036

Washing liquid

0.13

Oil

0.49

Terminal speed in honey is slower this is because the upthrust and viscous drag in honey are greater than the other two liquids.

Evaluation

There were a few wayward results. This could have been because human error on the time reading. Also I noticed that the honey was not pure, some little solid pieces seemed to float in it. These could have slowed the ball bearing and therefore a higher value of viscosity.

Also I am not very sure whether the ball bearing really reached terminal velocity, as the cylinders probably were not long enough for the ball bearing to reach terminal velocity. If I used longer cylinders I would have been able to mark more distances on the cylinders and make more time readings, until I was sure enough that the ball was really moving with constant speed.

In the absence of longer cylinders one way to improve the experiment would have been to give the ball bearing a high enough initial speed which would let the ball bearing to reach terminal speed quicker.

Comparing Viscosities        Page  of         09/04/2003

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