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Calculating the viscosity of Glycerol.

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Calculating the viscosity of Glycerol


Viscosity is a measure of the resistance against the flow of a substance (fluid). The higher the viscosity of a fluid, the less easily it can flow. The viscosity of a fluid can be calculated by using Stroke’s Law, which relates the viscosity of a fluid to the viscous drag (opposing force) and velocity at which it is travelling. One method of calculating the viscous drag (also the method I will be using) is by subtracting the upthrust exerted by the fluid on an object (ball) from the weight of the object as it is dropped through the fluid, assuming that the object has reached it’s terminal velocity and therefore has equal forces acting on it.


To observe and record the terminal velocities of different sized balls falling through Glycerol, and hence calculate the viscosity of Glycerol.


The only variables that will be changed for us to gain a range of results will be the size of the balls.

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  • Cylindrical tubing (blocked off at bottom)
  • Rubber bands/tape for marking start and stop distances
  • Metre ruler, stopwatches and micrometer
  • Glycerol and set of different sized balls (densities assumed to be the same and constant through the balls and fluid)
  • Measuring tube/flask and balance to obtain a volume and mass for the calculation of densities.


        For this investigation, I am not expecting to obtain perfect results as there are a number of errors that are likely to occur due to the limitations of our apparatus and judgement. For one, the times we obtain may not be absolutely correspond, as we our using our own eyesight and stopwatches to gain this measurement, and is therefore limited to the speed of our reaction. Also, it cannot be guaranteed that the balls we use have gained maximum velocity, although the results may show that there is very little variation in the times (especially with larger balls, as their mass and therefore weight will cause them to move faster). I am also predicting that the graph we plot of radius2

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        There are many improvements that can be made to give more accurate results for this experiment, although most of the changes that could be made do not include much that is possible with the apparatus that was provided. However, if more accurate and precise apparatus were to be used to take measurements, it would not dramatically affect the results over the length of tubing that is suitable for the conditions we had to work under. The main reason as I suggested before, for our inconsistent results was due to the balls not having reached their terminal velocity. The only method of allowing these balls to reach their terminal velocity would be to let them fall for a larger distance before recording the time’s. This is one improvement that could significantly better the experiment, any others being new methods of measuring the densities and velocities more accurately, maybe by using an electronic speedometer.

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