Why should we get rid of the bubbles in the tubes during the viscosity experiment?

Viscosity: Viscosity is the "resistance to flow" of a fluid.

The Viscosity Experiment

• Fill a graduated cylinder with glycerin.


• Drop six different sized steel balls, one at a time, into the glycerin.


• Video each steel ball as it travels through the glycerin.


• Use the information from the videos to characterize the flow of the glycerin around a sphere, determine the dependence of the terminal velocity on radius, and determine the dependence of the acceleration profile on radius.

Sources of Error

• Viscosity is affected by temperature.


• Instrument resolution can introduce errors.


• 
  Bubbles in the path of the ball reduce the viscosity of the glycerin.


• Bubbles that are attached to the ball increase the viscosity of glycerin.

Therefore, it is important to remove bubbles from the tubes (graduated cylinders), because they can artificially increase or decrease the viscosity of the fluid.