Unit A: Mix and Flow of Matter Topic 4: Flow Rate and Viscosity

Viscosity: the property that describes a liquid's thickness or thinness

- Viscous: a thicker liquid· Viscosity is a property of all fluids (liquids and gases)

·· Some liquids can flow faster than other liquids. · From what you know, rank the following list of liquids from fastest flowing (1) to slowest flowing (4):

Water _____Honey _____Vegetable Oil ______Molasses ______

Flow Rate: the time it takes for a fluid to flow from one point to another point.

Investigation 1F: Determining Flow Rate page 41-43Question: How fast can different liquids flow?

Product Performance and Viscosity

· Why might it be important to determine the flow rate and viscosity of a liquid?

· Viscosity is an important property that must be measured very precisely in some industries

Ex. Manufacturing lipstick Figure 1.22 page 45· The viscosity of cosmetics such as mascara, lipstick, and nail polish depends on the amount of solvent added.· Solvents keep the ingredients dissolved and fluid while applying, then evaporate to leave a dry, solid finish· People in many occupations need to know how to adjust the viscosity of a substance to suit needs (ex. chefs, mechanics, artists, technicians, etc.)

Product Performance and Viscosity

· Why might it be important to know how to determine the flow rate and viscosity of a liquid?· Viscosity of liquids is an important property that must be measured precisely in some industries· The cosmetics industry depends on flow rate and viscosity

Ex. Lipstick manufacturing page 45

Product Appeal and Viscosity

· People in many occupations need to know how to adjust the viscosity of a substance to suit needs (ex. chefs, mechanics, artists, technicians, etc.)

· Food manufacturers need to ensure that their foods are the right consistency (thickness) for their consumers· They must also know to regulate the effect of heat on the viscosity of a substance

How Does the Viscosity of Liquids Vary?

Liquids flow at different rates because they have different viscosities

- Particles can move around, but it might be difficult for them to pass each other (resistance to flow)

- This creates internal friction- It is easier for some fluid particles to move past each other than

other fluid particles- Attractive forces between some particles are stronger than

others

The viscosity of a liquid DECREASES as it is HEATED, and INCREASES as it is

COOLED.

- As the temperature of a substance increases, the attractive forces of the between the particles decrease. As the temperature of a substance decreases, the attractive forces between particles increases.

- Warmer liquids flow more quickly and cooler liquids flow more slowly

How does the viscosity of gases vary?

- Gas particles flow differently than liquid particles- Gas particles are far apart, so the attractive forces are

low, and the type of gas particle isn't as important- Gas particles collide rather than slide past each other- If gas particles are moving in the same direction, viscosity

will be low, BUT as they gain energy and move faster, gas particles will collide more and viscosity will be highEx. Balloon releasing gas

- The temperature of a gas directly affects viscosity

The viscosity of a gas INCREASES as it is HEATED, and DECREASES as it is

COOLED(this is the opposite of liquids)

Why?

Topic 4 Review page 49

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