Post on 15-Apr-2018
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).