Overview
1. Properties of Fluids
a. Predict how temperatures affects the flow of rate of liquids
b. Compare the viscosities and densities of various substances and understand the
relationship between the two properties
c. Describe the difference between mass and weight
d. Explain how buoyancy and gravity are related
e. Use the particle theory of matter to compare the densities of solids, liquids and gases to
describe effects of temperature on fluids
f. Compare what happens to different fluids when an external pressure is applied or when
the temperature is changed
2. The Use of Fluids
a. Plan and conduct an investigation to compare the densities of liquids and solids
b. Explain how the buoyant force on an object can be altered
c. Explain how the properties of fluids are used in design of technical innovation
d. Compare how liquids and gases transmit force in hydraulic and pneumatic systems
3. Fluids and Living Systems
a. Compare how fluids function in living things and manufactured devices
b. Explain how the study of hydraulics and pneumatics increases understanding of fluids in
the human body
A Close Up Look At Fluid Flow (p. 8)
- fluids are substances that flow
- FLOW RATE – how quickly a fluid flows
- DYNAMIC – systems involving moving fluids
- AERODYNAMICS – air moving around solid objects
- HYDRODYNAMICS – refers to motion of liquids around solid objects
Solids That Seem To Flow (p. 9)
- only liquids and gases require a container
- solids can be piled in a heap
Explaining Flow Using the Particle theory
- PARTICLE THEORY – a model to help us understand differences between fluids and solids
- 1. all matter is composed of particles
- 2. particles are in constant motion
- 3. forces of attraction among particles
- When solid; particles are close together and forces of attraction are strong
- Liquids; particles are moving more rapidly, forces of attraction are not as strong, particles can
‘slide’ over one another – aka. flowing
- Gases; particles are so far apart from each other and forces of attraction are weak, particles
can now move independently
Hand out sheet and complete in class. Take up answers.
Fluid Flow Around Objects (p. 10)
- shape of an object determines how fluids flow around
- LAMINAR FLOW – straight or almost straight line
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TURBULENT FLOW – water is irregular, broken or choppy
Refer to fig. 1 on page 10
Draw picture of figure 1 on blackboard.
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shapes that produce laminar flow have less air or water resistance that shapes that produce
turbulent flow
DRAG – resistance
Less drag means better fuel efficiency
STREAMLINED – shapes that create laminar flow that are aerodynamic
Wind Tunnels: A closer Look At Gas Flow
- wind tunnel has a propeller at one end that propels air into it
- smoke is often added to make flow visible
- engineers use wind tunnels to test airflow (ie. Airplanes, cars etc.)
Laminar Flow
Turbulent Flow
 give examples to fit under each of these headings
Viscosity: A Property of Fluids (p. 12)
- VISCOSITY – resistance that a fluid has to flowing movement
- particle theory helps us to understand that this resistance is due to the forces of attraction
among particles
- stronger the attraction among particles, greater the resistance of particles to flowing past one
another
- ketchup – high viscosity, syrup – lower viscosity
- viscosity is a concern when fluids are moving
Measuring Viscosity (p. 13)
- may use thick or thin to describe but not enough info.
- VISCOMETER – instrument that measure viscosity
Measuring Matter: Mass, Weight and Volume
Mass and Weight
- when people for refer weight, most actually mean the mass
- MASS – amount of matter in an object, stays constant
o Measured in grams or units from grams such as kg or mg
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WEIGHT – measure of force of gravity pulling on the object
o Measured in Newtons – after Sir Isaac Newton
o Object’s weight can vary according to location in the universe
o People on earth use weight and mass interchangeable because gravity on earth is
approximately the same as mass
Volume
- VOLUME – measure of amount of space occupied by matter
- Measured in cubic metres (m3) or litres
- Capacity is related to volume
- CAPACITY – measure of amount of space available inside something
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Measuring Liquids
measured by observing how much of a container they fill
if look at a container from side, may notice a slight curve at the edges of the surface
MENISCUS – curved surface of a liquid in a container
Measuring Volume of Solids – Rectangular Solids
may be measured with a ruler
use formula:
o volume = length X width X height (cm3)
Measuring Volume of Solids – Irregular Solids
- measured by displaclement
- DISPLACEMENT – technique used to measure the volume of a small irregular solid using
formula:
o volume of object = (volume of water + object) – (volume of water)
Measuring volume of Solids – Large Irregular Solid
- use displacement but recognize that the displacement must take place in another container
- overflow of fluid
- refer to page 19
Measuring Volume Activity
- give kids 3 cards with: displacement, linear volume (LxWxH) and overflow
- pick various items and kids hold up cards to decide how they would measure it
Relating Mass and Volume
Write up experiment. Hand out assignment.
Density: Another Property of Fluids
- DENSITY – the mass of a subject per unit volume
o Expressed as g/cm3
o Calculated by formula:
 Density = Mass/volume OR D = M/V
 Here are some practice questions:
Density = M/V
Mass (M)
5 kg
1000 kg
50 kg
Volume (V)
25 me
1 m3
2m
Density Is a Property of Fluids and Solids
- the ratio of mass to volume is constant for each fluid and that each fluid has its own density
- solids also have their own unique densities
- those that float = less than 1.00 g/mL
- those that sink (ie. Solids) = more than 1.00 g/mL
Homework. pg. 23 Q3a-c (3 marks for each part)
Comparing Densities
- pure substances has its own characteristic density
- solid usually have greater densities then gases
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-particle theory can help to understand
Copy figure 1 onto board for students.
Using Pure Water as a Standard
- we use pure water as a standard to compare all other densities
- comparing densities will allow us to determine which substances will float
- more dense substances sink below less dense ones
The Ups and Downs of Buoyancy (p. 28)
- when you jump into a pool, the water displaces to make room for you
- fluid also pushes back in all directions on the object
- upward part of the force exerted by the fluids is called BUOYANCY
Archimedes’ Principle
- a greek mathematician was asked to determine whether the king’s crown was made of pure gold
- he found that the crown appeared to weigh less in water than a bar of pure gold with the same mass
- this meant that there was greater buoyant force on the crown
- Archimedes realized that the crown displaced more water than the gold bar
- since was the original volume of water was the same, the crown displaced more water – therefore, NOT
pure gold, but had something else added to displace more water
- ARCHIMEDES PRINCIPLE – buoyant force on an object immersed in a fluid is equal to the weight of
the fluid that the object displaces.
How and Why Do Things Float?
- shipbuilders take dense material and make it float (ie. steel) by changing the shape
Forces Acting on a Floating Object
- if the upward force on an immersed object is greater than the downward force of gravity, object
will rise.
- opposite is also true
- BUT Archimedes’ principle says that the buoyant force on the object equals the weight of the
fluid it pushes aside
- SOOOO, the object will rise or sink depending on whether it weighs less or more than the fluid
it displaces. (give an example where the fluid can change such as jello or salt water or oil)
- POSITIVE buoyancy – object rises
- NEGATIVE buoyancy – object sinks
- NEUTRAL buoyancy – remains level
Buoyancy in Air
- buoyant forces in gases acts the same way as in liquid
- the only difference is the original densities of air, which can affect how one wants to change
buoyancy
Homework. p. 31 Q2 (2 marks), Q3 (1 mark each), Q4 (2 marks)
How Does Temperature Affect Viscosity and Density (p. 38)
- fluids run more easily when they’re warm
- as heat is taken AWAY from a fluid, its particles slow down and come closer together (Particle Theory)
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- this casues the fluid to contract, decreasing the volume, therefore, the density will increase (more
resistant)
- viscosity increases at lower temperatures
- when heat is added to a fluid, density and resistance to flow decreases
- as air is heated and released, balloon rises
Water – A Special Case
- water behaves differently from other fluids
- warmer water is less dense and floats on top of cooler water
- when swimming in a lake, stay on the top portion of the water since it is warmer
- BUTTTTTTT, as temperature drops below 4 degrees Celsius, it becomes less dense again (ice)
Refer to table 1 on page 38
- this unique property of ice floating keeps lakes from freezing solid in the winter
- as water cools, it sinks to the bottom and the ice insulates the water beneath
Explaining the Effect of Temperature Changes Using the Particle Theory
- in solids, particles are closely packed together and held in a rigid structure by forces of
attraction
- particles can move but only by vibrating in same place
- as more heat is added, speed of vibration becomes faster and the forces of attraction cannot hold
the particles together
- structure falls apart, melting occurs and a liquid is formed
- as more heat is added to liquid, again particles move faster and forces of attraction are further
broken
- particles start to escape and a gas is formed
- reverse process occurs as temperature decreases
- viscosity of fluid decreases as attraction between molecules weakens
Homework:
p. 39 Q1 (7 marks), Q2 ( 9 marks)
Confined Fluids Under Pressure (p. 44)
- confined fluids cannot leave or enter the system
- an example is blood moving through body as long as there is no open wound
- when fluids are confined, very interesting effects
- applying a force to one part of a system causes movement in another part of the system
- in air filled systems, there is a delay in the effect
- in water filled systems, the response is immediate
Using the Particle Theory (p. 45)
- in a liquid, the spaces between particles are already small
- when an external force is applied, only a small decrease takes place in the liquid’s volume
- in a gas, particles are father apart and for the force to be transmitted from one particle to
another, volume of gas must be reduced
- in other words, there is a delay in the response of a gas filled system
- it takes times to compress the gas before getting a response
- by applying enough pressure to a gas or liquid, particles can be pushed together that the gas can
change to liquid (ie. propane) or to a solid
Pressurized Fluid Systems: Hydraulics
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- HYDRAULICS – confined, pressurized systems to move liquids
What Makes Up a Hydraulic System?
- liquid put into a hydraulic system is hydraulic fluid
- oil is pushed into a cylinder and the oil pushes the piston into the cylinder
- valve controls the flow of oil
- Refer to fig. 1 on pg 46
Pumps and Valves
- pump is used to create a flow of fluid
- pumps often make fluid flow against gravity
- ie. water tap
The Heart: A Pressurized Fluid System
- the heart is essentially a pump with valves that pushes blood around your body
Pressurized Fluid Systems: Pneumatics
- PNEUMATICS – confined system that uses moving air or other gases
What Makes Up a Pneumatic System
- similar to a hydraulic system except that the air compressor is used
The Lungs: a Pneumatic System
- when we breathe, the diaphragm contracts adjusting the pressure of air in our lungs
- the diaphragm works in the same way as a plunger in a syringe
Design Challenge:
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