Grade 8Discovering Science Unit 3: Fluids and Viscosity
Chapter 7 Viscosity describes a fluid’s resistance to flow.
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?
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.
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
Fluids • A fluid is anything that flows. • Example: Water, maple syrup, milk, motor oil, Cheese Whiz, compressed air in tires, ...
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
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.
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
Chapter 8 Density describes the amount of mass in a given volume of a substance
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.
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.
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.
Calculating Density Formula: Word Problem: 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 • Density (D) = Mass (m) / Volume (V) D = m/V
Calculating Volume Formula: Word Problem: 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 • Volume (V) = Mass (m) / Density (D) V = m/D
Calculating Mass Formula: Word Problem: 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 • Mass (m) = Volume (V) x Density (D) m = VD
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
Chapter 9 Forces influence the motion and properties of fluids
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
Types of Forces • Buoyancy • Magnetic • Gravity • Friction
Forces Balanced Forces: Unbalanced Forces: One force is greater than another Kinetic energy – energy in motion/ • Balanced forces are equal to each other and opposite in direction to each other. • Potential energy - stored energy; energy at rest.
Mass vs. Weight Mass: Weight: 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. • Mass remains the same no matter where an object is in the universe.
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.
Objects Which Have Buoyant Forces Acting Upon Them • Boat • Hot air Balloon • Airplane • Swimmer • Parachutist
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.
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.
Design Influences an Object’s 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.
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.
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.
Force, Area and PressureTwo General Conclusions 1.) The larger the force, the greater the pressure. 2.) The smaller the area, the greater the pressure.
Calculating Pressure Formula: Word Problem: 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 • 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)
Calculating Force Formula: Word Problem: 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 • Force (F) = Pressure (P) x Area (A) F = P x A
Calculating Area Formula: Word Problem: 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 • Area (A) = Force (F) / Pressure (P) A = F / P
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).
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?
Pascal’s Law • Pascal’s 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
Application of Pascal’s Law • A car lift • An hydraulic jack • Automatic breaking system
Hydraulics vs. Pneumatics • Hydraulics is the study of pressure on “fluids”. • Pneumatics is the study of pressure on “gases”.
New Technologies Hydraulic System Pneumatic System Devises which exert/transmits force on continuous enclosed gas. Examples: Air compressors, jack hammers, air nail gun, ... • Devices which exerts/transmits force on a continuous, enclosed liquid. • Examples: dentist chair, dump truck, loaders, car lifts, human circulatory system...