1

Unit B – Fluids Chapter 4 – The Properties of

FluidsChapter 5 - The Use of FluidsChapter 6 – Fluids and Living

Things

2

Chapter 4 – The Properties of Fluids

Key Ideas• FLUID FLOW IS IMPORTANT WHEN AN OBJECT IS MOVING THROUGH A FLUID

OR A FLUID AROUND AN OBJECT• FLUIDS CAN BE DESCRIBE USING THEIR PROPERTIES• THE KINETIC MOLECULAR THEORY CAN EXPLAIN THE BEHAVIOUR OF

FLUIDS• TEMPERATURE CAN AFFECT THE PROPERTIES OF FLUIDS

3

4.1 – A Close-Up Look at Fluid Flow

4

Fluids are things that flow – Gases & Liquids Fluids flow because some sort of force is pushing or

pulling them

FORCE – a push or pull that causes movement The most common force is the force of gravity

FLOW RATE – how quickly a fluid flows in a given amount of time

Fluids Flow

5

Fluids Flow Systems that involve

movement, such as moving fluids, are said to be dynamic

Air or gas moving around solid objects is referred to as aerodynamics

Water or liquids moving around solid objects is referred to as hydrodynamics

6

Solids That Seem to Flow

Some solids can be poured (powder, sand) and can appear to flow but these are not fluids

If it can form a pile – it is not a fluid

7

The Kinetic Molecular Theory

All matter can exist in three states and can change from one state to another Solid Liquid

Gas

The Kinetic Molecular Theory is a model that helps us understand how matter can change from one state to another.

8

Kinetic Molecular Theory

The Kinetic Molecular Theory states that:1. All matter is made up of very small

particles (molecules and atoms)2. Particles are constantly moving

I. Solids – particles packed so tight that they can only vibrate

II. Liquids- particles farther apart so they can slide past each other

III. Gases- particles very far apart, move quickly

3. There are forces of attraction among particles

9

Kinetic Molecular Theory

10

Temperature and Changes of State

11

Forces of attraction between particles are strong when they are close together

Particles cannot flow in a solid b/c the force of attraction between them is too strong

Liquids and gases can flow because the molecules have enough energy to break the forces of attraction between the molecules

Explaining Flow Using the Kinetic Molecular Theory

12

4.2 – Fluid Flow Around Objects

13

Shape of an object determines how fluids flow around it

Laminar Flow- Flow in which a fluid travels in straight, or almost straight lines

Turbulent Flow- fluid flow characterized by irregular patterns when a fluid is unable to travel in straight lines

14

Shape of an object determines how fluids flow around it

Drag- A force (air or water resistance) that acts to slow an object moving through a fluid.

Streamlined- shaped to create laminar flow, has less air or water resistance (less drag) also called aerodynamic

15

Wind TunnelsResistance and Aerodynamics

16

4.3 – Viscosity: A Property of Fluids

VISCOSITY- The resistance of a fluid to flowing and movement

17

The Kinetic Molecular Theory helps us understand that resistance is due to the forces among particles

COHESION – The attractive forces among the particles of the same substance

The stronger the forces of attraction are, the greater the resistance of particles moving past one another

Viscosity

18

ADHESION – The attractive forces between the particles of a fluid and the particles of another substance The reason why ketchup sticks to the sides of a

bottle

Viscosity

19

SURFACE TENSION

In liquids, the attractive forces among the particles at the surface are greater than the attractive forces among the particles deeper in the liquid – this is called surface tension

SURFACE TENSION– The increased attraction among the particles at the surface of a liquid

20

An Instrument that measures viscosity is called a viscometer

Measuring Viscosity

21

4.5 – Measuring Matter: Mass, Weight, & Volume

22

Mass– the amount of material in an object An object’s mass stays constant everywhere in the

universe Mass is measured in grams (g) (kilo, milli, micro)

Weight– a measurement of the force of gravity pulling on an object An object’s weight varies depending where it is in the

universe Weight is measured in Newtons (N)

Mass & Weight

23

Mass vs. Weight

24

Volume– a measure of the amount of space an object occupies. It is measured in cubic meters, cubic centimetres,

litres, or millilitres

Meniscus– curved surface where a liquid contacts the wall of a container Forms due to the adhesive forces between the fluid

and the container

Volume

Measuring Volume Measuring the Volume

of a Liquid: You can measure a small

volume in a graduated cylinder

Remember to read the volume from the bottom of the meniscus at eye level

Measuring Volume Calculating the Volume

of a Rectangular Solid: Volume = length x width x

height

If you measure all the sides in centimetres then the volume will be in cubic centimetres (cm3)

*REMEMBER* - one cm3 = one mL

Measuring VolumeCalculating the Volume of an Irregular Solid: Use technique called DISPLACEMENT

Volume of solid = (volume of water + solid) – volume of water

Measuring Volume

Calculating the Volume of an Irregular Solid

4.7 – Density: Another Property of Fluids

DENSITY – Mass per unit volume of a substance

Using Density

It is expressed as grams per cubic centimetre (g/cm3) or grams per millilitre (g/mL)

Density is calculated by dividing the mass of an amount of a substance by its volume.

Density= mass/volume or D=m/V

31

Density is a Property of Fluids and Solids

32

4.9 – Comparing Densities

33

Comparing Densities – Things to Remember

Each pure substance has its own characteristic density

Solids have greater densities (usually) than liquids, and liquids have greater densities than gases

34

What portion of an iceberg is submerged?

35

4.10 – The Ups and Downs of Buoyancy

The volume of fluid displaced is equal to the volume of the object in

the fluid

36

Buoyancy Buoyancy – The upward

force that a fluid exerts on an object

Buoyancy is not the only force that acts on an object in a fluid – The force of gravity (weight) also acts on the object

37

Archimedes Principle

Archimedes Principle – the buoyant force on an object immersed in a fluid is equal to the weight of the fluid that the object displaces

38

4.11 – How and Why Do Things Float?

39

Positive Buoyancy- the tendency of an object to float or rise in a fluid because the object weighs less than the fluid it displaces

Neutral Buoyancy- The tendency of an object to remain at a constant level in a fluid because the object weighs the same as the fluid it displaces

Negative Buoyancy- the tendency of an object to sink in a fluid because the object weighs more than the fluid it displaces.

Forces Acting on a Floating Object

40

Forces Acting on a Floating Object

41

Buoyancy acts on objects immersed in a gas the same way it acts on objects immersed in gas – however there is ONE big difference between them

Density – the density of air is about 1/800 of that of water

You must displace a much greater volume of air to “float” in it

Buoyancy in Air

42

Buoyancy in Air

Buoyancy in Water Buoyancy in Air

43

Plimsoll Lines

44

4.12 – How Does Temperature Affect Viscosity

and Density?

45

How Does Temperature Affect Viscosity and Density?

Fluids run more easily when they are warm

Viscosity, density and buoyancy all change with changes in temperature

What happens when a fluid is cooled? How would this affect density if we know that d=m/v

46

Water: A Special Case

Water behaves differently from other fluids when the temperature changes