Science Focus Topic 5 Notes: Particle Theory and Viscosity | Print |

What is a fluid?
You probably think of a fluid as a liquid, but a fluid is simply anything that can flow.

This includes liquids, but gases are fluids too.
You can demonstrate that a gas flows, by doing Activity 2-1, p. 61
A fluid is anything that flows. P. 60

Particle Theory

All matter is made up of tiny particles.

The particles must move freely past one another and at rest have a flat surface.

For this reason, solids do not flow, because at rest, they form a cone-shaped heap. p. 62


Key Concepts:

  • Liquids that are thicker than others are more viscous, p. 65
  • Compare the viscosity of different liquids (Activity 2-3, p. 66)
  • Use a simple lab test to predict the effects of temperature changes on viscosity of fluids
  • Recognize flow rates as an indicator of the viscosity of different liquids
  • Identify applications, where viscosity of fluids is a significant factor (e.g. motor oils, sauces)

Definition of Viscosity

Viscosity is a liquid's thickness, or resistance to flow.

Measurement of Viscosity

Flow rate is a measure of a liquid's viscosity
The flow rate of a fluid is measured in ml/s (milliliters per second)
By measuring the flow rate, we are able to compare the viscosity of different fluids. (Activity 2-2 Activity 2-3)
The thicker the fluid, the slower it flows and the more viscous it is. (Activity 2-2, p. 66, 67)

Changing Viscosity

Temperature affects the viscosity of a fluid (Activity 2-4 p. 70)

  • Increasing the temperature of a fluid will lower its viscosity. p. 70
  • Lowering the temperature of a fluid will increase its viscosity. p. 70

Practical Applications pgs. 68-70

The principles of aerodynamics, drag and turbulence are associated with the concept of viscosity. Examine why these principles are related to how thick a fluid is.

Question: Taken the same aerodynamically designed racing car is on the track at different times of the day, which car would have an advantage, the
one running in the morning when the outside temperature is 10
oC, or the one running in the late afternoon, whern the outside temperature is 26oC ?

Use the particle theory and what you have learned about viscosity of fluids to explain your answer.

Motor Oil is used as a lubricant in engines at different temperatures in different regions and in different seasons of the year.
Fluids are moved across the country through pipelines.
Heaters are used to control viscosity along the length of the pipeline.

Extraction of oil - (Alberta Oil Sands) Only 25% can be extracted by conventional methods, whereas, 75% can be extracted by lowering the viscosity of the oil in the ground, before trying to extract it.
Cleaning: products that can have their viscosity adjusted by changing the temperature
(e.g. to remove bubble gum from a shoe or carpet, lower the temperature, by using an ice cube, to make the bubble gum more viscous, then it will be easier to remove)

Cooking requires knowledge of the effects that temperature has on viscosity.