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Grade 8
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A fluid is anything substance that flows
Honey, water, and lava are all fluids – but so
are gasses such as oxygen and carbon
dioxide
We use fluids to help us improve our lives
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Fluids can transport solids
A mixture of water and solids is called a
slurry
The paper that you write on was once a slurry
of wood pulp and water
Hydroseeding is the process of spraying a
slurry of seeds, fertilizer and sawdust to plant
difficult to reach areas
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Fluids can hold other materials
For example, the cytoplasm in your cells hole
the organelles that allow a cell to grow and
replicate
Toothpaste is a fluid that holds materials
designed to clean, polish and protect your
teeth.
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A slurry of water and cement is easy to
transport. As it hardens it can be shaped to
become a smooth, level concrete sidewalk
Each of these photographs show fluids in use
1. How are our lives improved by each of the uses
shown
2. What environmental issues are raised by each
use?
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Matter is anything that has mass and volume
The Particle Theory of Matter is a theory that
describes matter. It explains the behaviour of
solids, liquids and gasses.
Copy the 6 postulates of the theory into your
booklet from page 198 in your textbook.
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The particle theory states that particles are
attracted to each other. However, particles in
some substances may be more attracted to
particles in other substances than they are to
each other
Particles in a liquid can overcome some of
their attraction to each other and slide past
each other. This is why liquids flow and take
the shape of their containers
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Gas particles can move so quickly and are so
far apart that they overcome almost all their
attraction to each other. This is why gasses
flow and spread out to all parts of their
container.
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When the temperature of a solid, liquid or gas
increase, its particles move faster and farther
apart – as a result the substance expands
Thermal expansion is an increase in the
volume of a substance in response to an
increase in its temperature
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Ketchup, like all liquids will flow. However, it
is designed to flow slowly so it will stay on
food.
Thickness or thinness of a fluid is called
viscosity.
Viscosity is the resistance of a fluid to flow.
Fluids with a high viscosity do not flow as
easily as fluids with a low viscosity
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Temperature can have a big effect
on viscosity
When heat is added to a liquid, the
particles move faster and move
farther apart. This allows the
particles to move past each other
more freely
As the temperature of a liquid
increases, its viscosity decreases.
The cooler the liquid, the slower it
flows.
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Temperature affects the viscosity of gasses
differently from how it affects liquids
Friction is a force that works to slow down
motion as a result of surfaces rubbing against
each other
The greater the rubbing, or friction between
particles in any fluid, the higher the viscosity
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BUT in gases, the higher the temperature,
the higher the friction and the higher the
viscosity. The warmer the gas, the slower it
flows.
As the temperature of the gas decreases, the
particles slow down and collide less often, so
there is less friction. The viscosity decreases.
The cooler the gas, the faster it flows.
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The flow rate of a fluid is a measure of speed
at which a fluid flows from one point to
another
The greater the viscosity, the lower the flow
rate.
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The amount of mass contained in a given
volume is called density
Density describes how closely packed
together the particles are in a substance
A substance is most dense when it is a solid,
and least dense when it is a gas
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Read page 216 in the textbook. Copy the
three points in your booklet.
If metal has a greater density than water –
how is it possible for metal boats to float on
water?
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If you consider the density of the air inside
the boat and the density of all the objects in
the boat, you would find that the combined
density of all parts of the boat is less than the
density of the water.
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Density is the ratio of mass to volume. The
unit for measuring the density of liquids is
usually grams per millilitre (g/ml)
You can calculate the density if a substance
by dividing its mass by its volume
Density (D) = mass (m)
Volume (v)
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A force is a push or pull on an object – but
you already knew that 
We measure force in newtons (N)
One newton is approximately equal to the
force that you would exert to hold up a
baseball.
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Buoyancy is the tendency of an object in a
fluid to rise or sink due to density
differences with its surroundings,
Gravity attracts matter downwards towards
the earths centre. A fluid however exerts an
opposite force that pushes matter upward.
This is called the buoyant force.
Read page 220 to fill out
the chart in your booklet.
Pressure is the amount of force
applied to a given area.
You may have felt the pressure of water when
you swim deep in water.
Air is a fluid and it exerts pressure around you
all the time. Air pressure is why your ears
may “pop” when you are on a plane.
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Air pressure changes with altitude
There is less air pressure if we travel to a
higher altitude, like a mountain, because
there are fewer layers of air above us and the
air there is less dense.
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Pressure in fluid also changes with its depth
For example, the weight of the water in the upper
part of a swimming pool presses down on the
water on the lower part of the pool
The greater the dept of water, the greater the
pressure at that point.
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If a fluid is allowed to move, it will always go
from an area of higher pressure to an area of
lower pressure
You make use of this property when you
drink from a straw. Your mouth creates an
area of lower pressure. The juice box is at a
higher pressure, so it travels up the straw and
into your mouth. Mmm.
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An increase in temperature results in an
increase in pressure.
When the temperature increases, the particles
move faster and hit the walls of the container
with more energy
If the volume of the container cannot
increase, its pressure increases, possibly
resulting in an explosion
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Compression is a decrease in volume caused
by a force
Compressibility is the property of being able
to be compressed
Materials in a liquid state are said to be
incompressible, which means they can not be
compressed easily
Your foot compresses the air
inside the soccer ball as you
kick it.
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A fluid system is a group of parts, including
at least one fluid, that interact with each
other and function as a whole.
Two examples found in nature are
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Our body’s circulatory system
The movement of sap in trees
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Blaise Pascal made an important discovery in
the mid 1600s.
Pascal’s Law states that when force is applied
to an enclosed fluid, the increase in pressure
is transmitted equally to all parts of the fluid.
For example, when you squeeze
a balloon in the middle and it
bulges evenly at either end
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Hydraulic systems are systems that use a
liquid under pressure to transmit a force and
do work.
Rescue workers use hydraulic systems in the
Jaws of Life to free people trapped in vehicles
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Liquids can not be compressed. This means
that when pressure is applied to a liquid in a
pipe or a tube, the force can be transmitted
over a distance
Hydraulic systems can multiply the force
exerted by a liquid.
Read pages 242-243 to explain how a hoist
works,
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A pneumatic system is a system that uses a
gas, usually air, under pressure to transmit a
force.
In order for a gas to be put to work in a fluid
system, it must first be compressed.
Two advantages of pneumatic systems are
safety and cost.
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A pump is a device that moves a fluid
through or into something.
For example, your heat pumps blood to your
lungs.
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Valves are devices that control the flow of
fluids
For example, turning a tap one way allows
water to flow out. Turning it the other way
closes off the flow of water.
Page 247 of your textbook describes 4
different types of valves.