Practical investigation into Viscosity in liquids (Stokes Law).

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Practical investigation into Viscosity in liquids(Stokes Law)


When dealing with fluid/mechanical systems, it is important to know what affects the rate of descent of an object through a liquid.

There are many factors that affect the descent of an object through a liquid such as:

1) Temperature of the liquid

2) Mass* of object

3) Size/surface area of object

4 Viscosity of liquid

5) Angle of descent


I would like to investigate the correlation between temperature and time of descent. Reading suggests that the colder the liquid the longer it will take for the object to reach the bottom.

Mass*& Surface area/size

Gravity accelerates at 9.81 ms-1 independent of mass. Hence increasing the mass will not affect the experiment of surface area. Thus using an object of various sizes it would be possible to investigate the proportionately of size on the descent of the object.


I feel it is important to investigate the affects of how a more viscous liquid would impede the progress of an object descending through a liquid. Therefore I have included this factor into my investigation.

Angle of descent

I would like to observe the affects of the object descending at an angle. Such at sediment in a bottle is there a way in which bottles should be stored that may hasten descent?


To investigate the rate of decent of an object falling through a liquid (simulated by a ball bearing) and investigate some of the factors that will affect this.


I have completed this investigation by using many simple experiments to reach a firm conclusion on the rate of decent of a ball bearing through a liquid.

Size/surface area of ball bearing

The first set of experiments was to show the speed of five differently sized ball bearings descending through water. All five ball bearings seemed to reach their terminal velocity at the same timed interval.

Viscosity of liquid

The second set of experiments was to show the affects of a more viscous liquid (engine oil) on the decent of a ball bearing. Using the same method as the experiment for surface area, the ball bearing took longer to descend through the liquid.


On the third experiment I varied the temperature of the oil. The difference was at a higher temperature the ball bearing descended faster through the liquid.

Angle of descent

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Finally the fourth experiment compared angles of which the ball bearing descended through a liquid. The results showed a greater angle to the vertical reduced the speed of decent through the liquid.

Initial apparatus

The following apparatus was used to complete the investigation:

2.2 metre plastic tube (colourless)
Diameter 0.03 metre

900ml Water
900ml Engine oil

Five ball bearings with diameter and masses as follows:

Class Mass (g) Diameter (mm)
Very small 0.12 2.96
Small 0.88 6.98
Medium 4.07 9.98
Large 8.96 13.98
Very large 16.69 16.9

Clamp and clamp stand.

Tape measure

Stop clock




Bunsen to heat oil (in a pan).


Each ...

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