Properties of Fluids
Viscosity
SCI 8: Fluids Unit
Curriculum Outcomes Addressed
- Design an experiment to test the viscosity of various common fluids and identify the major variables (208-6)
- Compare the viscosity of various liquids (307-6)
- Describe factors that can modify the viscosity of a liquid (307-7)
- Use a temperature-measuring technology effectively and accurately for collecting data in temperature-viscosity investigations (209-3)
- Demonstrate a knowledge of WHMIS standards by demonstrating the correct methods of disposal of various oils, for example (209-7)
- Identify and relate personal activities and potential applications to fluid dynamics (109-10, 112-7, 210-12)
• We will study the following properties of fluids:
1. Density
2. Buoyancy (Floating and Sinking)
3. Displacement (Archimedes’ Principle)
4. Viscosity
5. Pressure (Pascal’s Principle)
Key Terms
• Viscosity: “ A fluid’s resistance to flow.”
• Viscous: “Having a thick, sticky consistency
between solid and liquid; having a
high viscosity.”
What is Viscosity?
• Viscosity is the physical property of a fluid that
limits its ability to flow
• Viscosity only applies to fluids (liquids and gases)
because solids do not flow.
• The higher a fluid’s viscosity, the slower it flows.
• The lower a fluid’s viscosity, the easier/faster it flows.
In this example, viscosity increases
from left to right (left has lowest
viscosity, right has highest viscosity)
What Causes Viscosity?
• A fluid’s viscosity depends on its internal friction or
strength of particle bonds.
• If the bonds between a fluid’s particles are strong,
then viscosity is high, which means there is high
resistance to flow, and the fluid does not flow
easily (flows slowly).
• If the bonds between particles are weak, then
viscosity is low, which means there is low
resistance to flow, and the fluid flows easily (flows
quickly)
Practice Questions
1) If a fluid flows very slowly, what can you say about
its viscosity? Is this fluid viscous or not viscous?
2) If a fluid flows very easily/fast, what can you say
about its viscosity? Is this fluid viscous or not viscous?
Practice Questions - ANSWERS
1) If a fluid flows very slowly, what can you say about
about its viscosity? Is this fluid viscous or not viscous?
A fluid that flows slowly has a high viscosity.
We would say that this fluid is viscous.
2) If a fluid flows very easily/fast, what can you say
about its viscosity? Is this fluid viscous or not viscous?
A fluid that flows easily/fast has a low viscosity.
We would say that this fluid is not viscous.
Practice Questions
3) Name three liquids that have a high viscosity.
1.
2.
3.
4) Name three liquids that have a low viscosity.
1.
2.
3.
Practice Questions - ANSWERS
3) Name three liquids that have a high viscosity.
1. Molasses
2. Maple Syrup
3. Motor Oil
4) Name three liquids that have a low viscosity.
1. Water
2. Vegetable Oil
3. Pop
Order of Viscosity
• Order the following liquids from least to most
viscous (at room temperature):
–
–
–
–
–
–
–
–
–
–
–
Molasses
Honey
Water
Window Putty
Maple Syrup
Anti-Freeze
Blood
Shortening
Peanut Butter
Ketchup
Motor Oil
Order of Viscosity - ANSWER
• Order the following liquids from least to most viscous
• Centipoise: The unit of dynamic viscosity in the centimetre gram
second system (how many cms 1 gram of a fluid flows per second)
MATERIAL
APPROXIMATE VISCOSITY
(in centipoise)
Water
Blood
Anti-Freeze
Motor Oil or Maple Syrup
Honey
Molasses
Ketchup
Peanut Butter
Shortening
Window Putty
1 to 5
10
15
150 to 200
2,000 to 3,000
5,000 to 10,000
50,000 to 70,000
150,000 to 250,000
1,000,000 to 2,000,000
100,000,000
The Pitch Drop Experiment:
The Highest Viscosity in the World
http://www.smp.uq.edu.au/content/pitch-drop-experiment
Viscosity and Temperature
• How might the viscosity of a fluid be affected by
temperature? Make a two-sentence prediction by
filling in the blanks below.
As temperature increases, viscosity ________________.
As temperature decreases, viscosity _______________.