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Grade 8 · Science · Unit 4 of 13

Viscosity & Flow

Why some fluids flow fast and others creep

What your child practises

What viscosity is, how temperature and other factors change how fluids flow, and how to find a flow rate by dividing volume by time.

Ontario Curriculum expectation: C2.1, C2.8 · viscosity, volumetric flow rate and factors that affect the flow of fluids

Sample questions

A taste of this unit. In the app, questions change every time and get easier or harder to match your child.

  1. Question 1

    Two liquids are poured down the same ramp. Liquid A takes 12 s and liquid B takes 4 s. What can you conclude?

    • Liquid B has the higher viscosity.
    • Liquid A has the higher viscosity.
    • Both have the same viscosity.
    • Liquid A has the lower density.
    Show answer

    Liquid A has the higher viscosity.

    Hint: The slower liquid resists flowing more, so it is more viscous.

  2. Question 2

    A pump moves 150 mL of water in 10 s. What is the flow rate in mL/s?

    answer boxmL/s

    Show answer

    15 mL/s

    Hint: Flow rate = volume ÷ time.

  3. Question 3

    Why do engineers choose a lubricating oil with the right viscosity for an engine?

    • It must flow to every part and still coat moving surfaces.
    • It must be a solid to protect the engine.
    • Viscosity does not matter for oil.
    • It should be as thin as air.
    Show answer

    It must flow to every part and still coat moving surfaces.

    Hint: Oil that is too thick flows poorly, and oil that is too thin does not protect the parts.

  4. Question 4

    Why does paint get thinner and easier to spread when a little thinner is added?

    • Its density becomes zero.
    • It becomes a solid.
    • Its viscosity decreases.
    • Its viscosity increases.
    Show answer

    Its viscosity decreases.

    Hint: Diluting a fluid makes it flow more easily.

  5. Question 5

    Which of these is a gas?

    • oxygen
    • syrup
    • olive oil
    • milk
    Show answer

    oxygen

    Hint: Gases flow and spread out to fill their container.

  6. Question 6

    Which pipe lets the most water flow in the same time, if the pressure is the same?

    • a wide pipe
    • a pipe that is pinched shut
    • a pipe full of gravel
    • a narrow pipe
    Show answer

    a wide pipe

    Hint: There is more room for fluid to move through a wider opening.

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