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Unit B – Fluids Chapter 4 – The Properties of
FluidsChapter 5 - The Use of FluidsChapter 6 – Fluids and Living
Things
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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
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4.1 – A Close-Up Look at Fluid Flow
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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
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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
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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
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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.
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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 movingI. Solids – particles packed so tight that they
can only vibrateII. Liquids- particles farther apart so they can
slide past each otherIII. Gases- particles very far apart, move
quickly3. There are forces of attraction among particles
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Kinetic Molecular Theory
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Temperature and Changes of State
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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
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4.2 – Fluid Flow Around Objects
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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
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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
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Wind TunnelsResistance and Aerodynamics
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4.3 – Viscosity: A Property of Fluids
VISCOSITY- The resistance of a fluid to flowing and movement
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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
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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
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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
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An Instrument that measures viscosity is called a viscometer
Measuring Viscosity
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4.5 – Measuring Matter: Mass, Weight, & Volume
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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
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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 Volume
Calculating 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
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Density is a Property of Fluids and Solids
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4.9 – Comparing Densities
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When comparing densities why is air less dense than liquids?
Liquids and gas
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When looking at two substances does it’s density change as it changes state?
Use the kinetic molecular theory to explain why it does.
What happens to the volume of a substance when heat is added or taken away?
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Water is exception to the rule.
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If you have two 300ml bottles full of water that are the exact same size and you freeze bottle one and not bottle two?
Will one bottle get bigger? What the mass in each bottle stay the same? Will the
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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
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What portion of an iceberg is submerged?
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Calculate
Calculate the percentage of a piece of birch that would float on the surface of vegetable oil
Birch D = 0.66g/cm3 Oil D = 0.92g/cm3
Formula to find comparing densities
Density of solid / Density of liquid x 100 %
Would more or less of the birch float in water compared to oil?
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4.10 – The Ups and Downs of Buoyancy
The volume of fluid displaced is equal to the volume of the object in
the fluid
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How is buoyancy different that volume?
Try this Lump a ball a clay and drop it in water watch
how much water displaces Turn that lump into a bowl and submerge
into water see what happen. What did you notice.
Buoyancy
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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
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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
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Buoyant force = Weight in air (N) – Weight in liquid
(N)For example if 300g or clay weighs 2.9N in the air and 1.6 N in water what is the
buoyant force?
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4.11 – How and Why Do Things Float?
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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
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Forces Acting on a Floating Object
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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
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Buoyancy in Air
Buoyancy in Water Buoyancy in Air
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Plimsoll Lines
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What happens to a substance when it’s mass stays the same but it’s volume increases?
What are the three types of bouyancy?
The density of air is _______ of that of water? Which means in order for something to float in air you must?
Let’s Recap
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4.12 – How Does Temperature Affect
Viscosity and Density?
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Viscosity is the resistance of a fluid to flow and move
Like in the oil lab when happen when heat is added to the oil? Think about the oil’s molecules
What happens when heat is taken away from the oil? Think about the oil’s molecules
Viscosity
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Density Is the mass of a substance per unit volume of a substance. D = M/V
Generally, what happens to a liquids density when we heat a substance?
Hint – think about it’s molecules, now think about it’s volume.
Generally, what happens to a liquids density when heat is removed? Again think of molecules and volume.
Density
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How Does Temperature Affect Viscosity and Density?
As just discussed fluids run more easily when they are warm because molecules are able to slide past each other. Syrup!
Viscosity, density and buoyancy all change with changes in temperature
We also know that density changes as heat being added or removed affects it’s volume. Heat expand & cool shrinks.
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Water Behaves Differently
Water is the only liquid that has a reverse effect only when you remove heat.
What happens as you remove heat from water?
Hint think of an ice cube in water.
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Water: A Special Case
Water behaves differently from other fluids when the temperature changes
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Go into Skitch and Draw a picture of what molecules look
like at 0ºC, 4ºC and 8º C
