# Calculating the viscosity of Glycerol.

AS PHYSICS INVESTIGATION

Calculating the viscosity of Glycerol

## Introduction:

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.

Aim:

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

Variables:

The only variables that will be changed for us to gain a range of results will be the size of the balls. All other variables including the densities of both the balls and fluids must remain the same. Although temperature changes could cause expansions and contractions in the substances, it will not affect the results significantly as the changes will have an effect on both the fluid and ball, hence having no overall effect on the experiment. There may be other variables such as the gravitational force and density of Glycerol through the tube that we will assume to be constant, as any changes cannot significantly alter the final result.

Range:

To obtain the most accurate and reliable results we can get under the conditions given, I will be repeating the experiment with each size ball three times at least. To ensure that the maximum velocity has been reached by the falling balls (vital, as this is the only condition where the forces acting on it are equal), we will record two time’s consecutively with equal distances, comparing the times to check that they are reliably close. If this is not the case the terminal velocity may not have been reached, so the distance to the first mark ...