Grade 8 Discovering Science

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Grade 8Discovering Science

• Unit 3 Fluids and Viscosity

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Chapter 7

• Viscosity describes a fluids resistance to flow.

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QUESTIONS

• Why do some fluids seem to hold their shape
  longer?
• Why do some fluids take up more space than other
  fluids at different t temperatures?
• Why do some fluids flow slowly while other flow
  quickly?

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The Particles Theory

• All matter is made up of particles.
• These particles are constantly moving they have
  energy.
• There are spaces between these particles.
• There are attractive forces between the
  particles.
• The particles of one substance differs from the
  particles of other substances.

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The States of Matter
Properties Properties Properties Properties Properties
State Shape Volume Particle Arrangement Particle Movement
Solid Fixed Does not change Tight Vibrate
Liquid Unfixed Does not change Tight Flowing
Gas Unfixed Changes Loose Random
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The Changing States of Matter

• Melting - Solid to liquid
• Freezing - Liquid to solid
• Evaporation - Liquid to gas
• Condensation - Gas to liquid
• Sublimation - Solid to gas
• Deposition - Gas to solid
• Ionization - Gas to plasma
• Deionization - Plasma to gas

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Changing States of Matter - Continued
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Fluids

• A fluid is anything that flows.
• Example
• Water, maple syrup, milk, motor oil, Cheese
  Whiz, compressed air in tires, ...

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Viscosity

• The viscosity of a fluid is related to the
  amount of friction between particles
• Friction is the resistance to movement.
• Viscosity describes how thick or thin
  something is.
• Viscosity is how easily a fluid flows.
• Flow rate is the amount of fluid that flows past
  a point in a given amount of time

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Examples Viscosity

• Motor oil, in the winter, flowing from its
  container flows slow, but in the summer it flows
  fast.
• Pancake syrup, just out of the refrigerator,
  flowing from the bottle flows slow, but when
  warmed up by placing it under warm water will
  flow fast.
• relate to the particle theory.

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The particle Theory and Viscosity

• Several factors influence the viscosity of a
  fluid, they include
• Strength of attractive forces
• Temperature variations
• Concentration of the fluid
• Particle size

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Chapter 8

• Density describes the amount of mass in a given
  volume of a substance

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Density

• Density is the amount of mass in a certain unit
  volume of a substance.
• A bowling ball has a high density of particles in
  comparison to a balloon filled with helium gas or
  a glass of water.
• The particle theory, density and a thermometer.

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Density cont...

• Solid objects can move easily through liquids
  and gasses, while gases and liquids find it
  difficult to travel through solids, if at all.
• Gasses are less dense than liquids
• Liquids are less dense than solids
• Displacement is the amount of space that an
  object takes up when placed in a fluid.

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Calculating Density, Volume and Mass

• Density is the amount of mass in a certain unit
  volume of a substance.
• Volume is a measurement of the amount of space
  occupied by a substance.
• Mass is the amount of matter in a substance.

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Calculating Density

• Formula

• Word Problem

• Density (D) Mass (m) / Volume (V)
• D m/V

• Find the density of a substance with a mass of 25
  g and a volume of 4 cm3
• D m/V
• D 25 g / 4 cm3
• D 6.25 g/cm3

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Calculating Volume

• Formula

• Word Problem

• Volume (V) Mass (m) / Density (D)
• V m/D

• Find the volume of a substance with a density of
  8.5 g/ cm3 and a mass of 34 g.
• V m/D
• V 34 g / 8.5 cm3
• V 4 cm3

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Calculating Mass

• Formula

• Word Problem

• Mass (m) Volume (V) x Density (D)
• m VD

• Find the mass of a substance with a density of
  10.2 g/ cm3 and a volume of 3.4 cm3.
• m VD
• m 3.4 cm3 x 10.2 g/ cm3
• m 34.68 g

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Density Changes in Everyday Life

• Examples (Discuss)
• A baking cake
• Water (three states)
• Warms and cool tire pressure
• Drying wood
• Hot air balloons
• Salt water

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Chapter 9

• Forces influence the motion and properties of
  fluids

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Force

• A force is a push or pull.
• A force can start an object to move or stop an
  object from moving.
• A force can cause an object to speed up or slow
  down.
• A force can change the direction of a moving
  object.
• A force can be a bend, twist of squeeze.
• An arrow is used to symbolize force

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Types of Forces

• Buoyancy
• Magnetic
• Gravity
• Friction

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Forces

• Balanced Forces

• Unbalanced Forces

• Balanced forces are equal to each other and
  opposite in direction to each other.
• Potential energy - stored energy energy at rest.

• One force is greater than another
• Kinetic energy energy in motion/

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Mass vs. Weight

• Mass

• Weight

• Mass remains the same no matter where an object
  is in the universe.

• Weight is the measure of the push or pull, of
  gravity on an object.
• Weight is measured in units of Newton (N).
• The weight of an object on the moon is 1/6 of
  that on Earth. A 600 N person would weigh 100 N
  on the moon.

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Buoyancy The Anti-Gravity Force

• Buoyancy is the upward force of an object that is
  submerged or floating in/on a fluid.
• In other words buoyancy is the upward push of a
  substance away from the natural pull of center of
  the Earth.

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Objects Which Have Buoyant Forces Acting Upon Them

• Boat
• Hot air Balloon
• Airplane
• Swimmer
• Parachutist

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Archimedes Principle

• The buoyant force acting on an object equals the
  weight (force of gravity) of the fluid being
  displaced by the object.
• If the force of gravity pulling down on an
  object is equal to the amount of buoyant force
  pushing up then the object is said to have
  neutral buoyancy it will neither rise or sink.

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Salt Water vs. Fresh Water

• Fluids with high density (particles are closer
  together) exert a greater buoyant force than
  fluids with low density (particles farther apart
  from each other).
• Example Salt water is more dense than fresh
  water, therefore, object is salt water will float
  better than is fresh water.

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Design Influences an Objects Ability to Sink or
Float

• Concrete or steel boat vs. a chunk of concrete or
  a section of steal.
• A silk/canvass hot air balloon vs. a sheet of
  canvass.
• Submarine vs. an iron pole.

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Average Density

• The average density of an object is the total
  mass of all substances that make up the object
  divided by the total volume of the object.
• Ships can be built of steel because the haul of
  the ships can be constructed large enough to
  ensure the density of air in the haul is low.

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Pressure

• Pressure is the force acting on a certain area of
  a surface.
• Example When you place your finger on a bruise,
  you are applying pressure to that specific area.
  You are not applying pressure to your ankle, ...
  Just the bruise.

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Force, Area and PressureTwo General Conclusions

• 1.) The larger the force, the greater the
  pressure.
• 2.) The smaller the area, the greater the
  pressure.

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Calculating Pressure

• Formula

• Word Problem

• Pressure is calculated by measuring the force
  that is being exerted on an object and dividing
  it by the area over which the force is being
  exerted.
• Pressure (P) Force (F) / Area (A)
• P F / A
• Pressure is measured in units of pascals (Pa)

• A serving jug hold 500 N of Kool-Aid. If the
  base of the serving jug is 0.05 m2, what pressure
  does the Kool-Aide exert on the base of the
  serving jug?
• P F / A
• P 500 N / 0.05 m2
• P 10 000 Pa

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Calculating Force

• Formula

• Word Problem

• Force (F) Pressure (P) x Area (A)
• F P x A

• If 63 000 Pa of pressure is being exerted on a
  rubber ducky with a area of 0.09 m2, how much
  force is being exerted on the rubber ducky?
• F P x A
• F 63 000 Pa x 0.09 m2
• F 5670 N

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Calculating Area

• Formula

• Word Problem

• Area (A) Force (F) / Pressure (P)
• A F / P

• If 500 N of force is being exerted on a balloon
  creating pressure of 1600 Pa, what is the area
  of the object?
• A F / P
• A 500 N / 1600 Pa
• A 0.3125 m2

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Pressure, Volume and Temperature

• Increasing the temperature of a gas increases the
  volume of the gas (pressure being held constant).
• Increasing the temperature of a gas increases the
  pressure of the gas (volume being held constant).
• Increasing the pressure of a gas decreases the
  volume of a gas (temperature being held
  constant).

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Compression vs. Incompressibility

• Compression
• The ability to squeeze into a smaller volume.
• ex. Aerosol cans
• Incompressibility
• The inability to squeeze into a smaller volume .
• ex. Try squeezing a unopened 2l Pepsi bottle.
  What happened did not happened?

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Pascals Law

• Pascals law states that pressure applied to an
  enclosed fluid is transmitted with equal force
  throughout the entire container.
• Discuss
• Compressed air
• Propane cylinders
• Aerosol cans

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Application of Pascals Law

• A car lift
• An hydraulic jack
• Automatic breaking system

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Hydraulics vs. Pneumatics

• Hydraulics is the study of pressure on fluids.
• Pneumatics is the study of pressure on gases.

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New Technologies

• Hydraulic System

• Pneumatic System

• Devices which exerts/transmits force on a
  continuous, enclosed liquid.
• Examples dentist chair, dump truck, loaders,
  car lifts, human circulatory system...

• Devises which exert/transmits force on continuous
  enclosed gas.
• Examples Air compressors, jack hammers, air nail
  gun, ...