Viscosity Experiment

Topics: Force, Viscosity, Terminal velocity Pages: 10 (1686 words) Published: March 29, 2012
The aim of my investigation will be to analyse the relationship between several variables, which are defined by stokes law, and conclusively to apply these in order, to calculate the viscosity of the fluid from my results. To see how successful my experiment was, I will be comparing my results with those from external sources such as a Textbook; this would therefore determine how accurate my experimental results were.

All fluids, from liquids to gases illustrate the property of viscosity to some degree. Viscosity is caused by internal friction due to the strong intermolecular forces; hence it is affected by temperature in liquids. It is measured in Pascal’s per second unless the viscosity is kinematic. Viscosity can be thought of as fluid friction, just as friction between two solids resist the motion of one over the other, also possible to cause an acceleration of one fluid relative to the other.

Liquids will vary from “thin” having a lower viscosity like water, to “thick” having much higher viscosity like honey or treacle. There are many ways to measure viscosity, for example “the line spread test”, which involves a fixed quantity of liquid being allowed to flow out of a container and spread onto a flat surface or “redwood viscometer”, which involves the liquid to flow through a narrow tube driven by its own head of pressure, but due to the lack of apparatus, I chose to do the falling ball viscometer, as this experiment gave an absolute measurement of viscosity, and was too, the most feasible method to be performed in a lab.

I will be unable to calculate the viscosity using the above equation, because “F” will not be able, to be measured directly with the method I will be using. So I would rearrange the above equation to:

When the ball bearing is travelling at terminal velocity the net force is zero, because there is no acceleration. This is known when used in the equation F=ma. For the ball bearing to be in terminal velocity all forces acting on the ball bearing should be in equilibrium. This is to be achieved by the spheres weight acting downwards, and in addition to the drag force produced, there is either an up thrust or buoyancy force produced. Up thrust/Buoyancy always acts when an object is immersed in a fluid, the object displaces fluid around it, and hence it arises. Below is an image showing “Forces acting on a falling ball”.


So, what I will be expecting is, after the ball has been dropped into a liquid, it should first accelerate due to the downward force of its weight, I then predict that the viscous drag will increase due to the increase in speed, the downward force due to gravity will decrease, this is where acceleration stops. From this point the object is in terminal velocity, and will remain at this velocity, if no other force acts upon this object.

Before conducting the experiment there are several measurements I will have to record to calculate the viscosity of the fluid.

Measurements and Formula’s regarding Ball bearing ……..

The volume of fluid displaced is theoretically equivalent to the volume of sphere.

We can Write Down an expression for the forces acting on the ball bearing, which will combine to give a resultant force of zero.

We can now return to the experiment itself, as we have understood the theory lying behind calculating viscosity. I was conducting two experiments, one with varying temperature, and the other with different size ball bearings.


Planning, Equipment, 3 Different size ball bearings, Stopwatch, 3 Measuring Cylinders, 3 Water baths, set at 35oc 45oc, 25oC, Golden syrup, Weighting scale, Micrometre, 2 Spoon, and Tray

I used the micrometre for measuring the diameter of my ball bearing; this was the most appropriate instrument to use. The precision of the micrometre was to 0.01mm, which was

So, for my first experiment, I started...
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