The faster a liquid flows, the less viscous it is…… How is the ... · The greater the viscosity...

How is the flow rate of a liquid related to its viscosity?

The faster a liquid flows, ...the less viscous it is……

(or the other way around)

INVERSE relationship* (in science: often either

direct or inverse relationship)

HOMEWORK: In your notebook: p 281 Q 1 - 4 (brief answers)

1. What is meant by the flow rate of a substance?

Flow rate is a measure of the time it takes for a fluid to flow from one point to another. The shorter the time is, the greater the flow rate is.

2. What is the relationship between the viscosity of a liquid and its flow rate?

The greater the viscosity is of a liquid, the lower its flow rate is. For example, white glue has high viscosity, and flows very slowly.

HOMEWORK: p 2813. How can you test the viscosity of a liquid? (all measure flow rate)

Several tests:

1. Drop identical marbles into cylinders of fluids. The greater the viscosity is, the more time it takes for the fluid to reach the bottom. (drop test)

2. Pour the fluid into a container with a small hole in the bottom, and measure the volume of fluid that comes out in one minute. The greater the viscosity is, the smaller the flow rate is. (drain test)

3. Done in our lab session: Ramp test

HOMEWORK: p 2814. List two substances that have a low viscosity and two substances that have a high viscosity.

Low viscosity fluids: many alcohols, gasoline, water, butane in a butane lighter

High viscosity fluids: vegetable oil, motor oil, molasses, syrup, paint, glue, etc.

7.3 Factors that affect Viscosity:

1. Temperature:

2. Concentration:

3. Attractive Forces:

4. Particle Size and Shape:

1. Temperature:

Q) What is Kinetic Energy?

● the energy a particle has due to its motion

Kinetic energy = Speed of particles

Kinetic Energy depends on … temperature!

Kinetic energy=Speed of particles Temperature

….then

Kinetic Energy

Temperature and Viscosity of Liquids

↑ temp

Particles have more kinetic energy

Particles pull away from each other = ↑ flow

Viscosity ↓

Read P. 286...why do we sometimes “plug in” cars (block heater) on a cold night?

Temperature and Viscosity of Liquids

↓ temp

Particles have less kinetic energy

Particles are closer to each other = ↓ flow

-- Ice --

Viscosity ↑

Temperature and Viscosity of GasesThe effect of temperature on gas particles is opposite to the effect on liquids.

● Gas particles do not depend on an increase in energy (a rise in temperature) to move farther apart, as is the case for liquids. (The particle theory statesthat the particles in gases are already very far apart)

● When energy is added (increase temperature), gas particles speed up and collide with each other more often, causing an increase in internal friction, and therefore an increase in viscosity.

● Cooler temperatures in gases keep the internal friction of particles (and the viscosity) low.

Demo Balloon Experiment:(you will observe that a gas contracts when it cools).

1. What do you think happened to the temperature of the gas (air) inside the flask during this experiment?

2. How would you describe the kinetic energy of the particles of the gas inside the flask during the experiment?

3. How is the behaviour of the balloon related to the kinetic energy of the particles of gas inside theflask? ↑ temp then ↑ pressure….

Temperature and Viscosity of Gases

↑ temp

Particles have MORE kinetic energy

Particles speed up and bump into each other

Viscosity ?

See textbook

Page 294

particles in gas are

already far apart

↑ friction (bumping) = ↓ flow

Viscosity ↑

Fluid movement of gases● note that drifting smoke particles provide clues to the movement of the

surrounding gas

2) Concentration

Concentration = amount of a substance dissolved in a specific volume

______ concentration then _____ viscosity

P. 288 food examples...discuss

Chefs: Making gravy or sauces…(flour and water) If you increase the concentration of flour mixed with the water…

What happens to your sauce or gravy?

(or cornstarch and water)

3) Attractive Forces and Viscosity

● invisible attractive forces can be strong or weak

● it depends on the substance

Ex:

Water = weak attractionOil = medium attractionHoney = medium to strong attraction

Water molecule

Attractive Forces and Viscosity

- if weak attraction then particles pull apart and slide over each other easily

Flow is easy so….

Viscosity is lower

Water molecule

Attractive Forces and Viscosity

- if strong attraction then particles pull towards each other and do not slide over each other easily

Flow is difficult so….

Viscosity is higher

2 oil molecules

4) Particle Size and Viscosity

Small = Fast

Takes up less space and has more room to move Flows faster

so viscosity is ________

Particle Size and Viscosity

Big = Slow

Takes up more space and has less room to move

Flows slower

so viscosity is ________

Motor oil example

Viscosity and particle size

SYRUP WATER SOAP

Particle Theory of Matter...with a bit more info

1) All matter is made up of very small particles.

2) All particles in a pure substance are the same.

3) There is space between the particles.

4) The particles are always MOVING. As particles gain ENERGY, they move faster.

5) The particles in a substance are attracted to one another. The strength of the attractive force depends on the type of particle.

“Real” World Connection Steam (heat) is used in oilsands industry to alter viscosity of bitumen (oil).