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Unit B – Fluids . Chapter 4 – The Properties of Fluids Chapter 5 - The Use of Fluids Chapter 6 – Fluids and Living Things. 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 - PowerPoint PPT Presentation
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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 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
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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 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
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Density is a Property of Fluids and Solids
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4.9 – Comparing Densities
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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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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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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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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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4.12 – How Does Temperature Affect Viscosity
and Density?
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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
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Water: A Special Case
Water behaves differently from other fluids when the temperature changes