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Matter Ch. 18 - 20 Phases of Matter • Review… The four Phases of Matter are… 1. 2. 3. 4. Solids • Properties 1. Crystal Structure 2. Density Solids • Properties Cont… 3. Elastic Materials – Returns to original shape after distortion. (Ex. Slinky) • Elastic Limit – Distance at which permanent distortion occurs 4. Inelastic Materials – Do not resume original shape after distortion. (Ex. Clay) Solids • For Elastic Materials… – Hookes Law - the amount of stretch (or compression), is directly proportional to the applied force. F ~ ∆x Solids • Compression and Tension Between the top and bottom, there is a region that is neither stretched nor compressed. This is the neutral layer. Compression and Tension • I-Beams – An I-beam is like a solid bar with some of the steel scooped from its middle where it is needed least. The beam is therefore lighter for nearly the same strength. Scaling • The study of how size affects the relationship between weight, strength, and surface area. An ant can carry the weight of several ants on its back, whereas a strong elephant could not even carry one elephant on its back. If an ant were scaled up to the size of an elephant, would it be several times stronger than an elephant? Scaling • As the size of a thing increases, it grows heavier much faster than it grows stronger. • How scaling affects strength – Weight depends on volume – Strength comes from the area of the cross-section of the limb. Ex’s. Tree limbs, animal limbs… Scaling • A 1-cm cube has a cross section of 1 cm2 and its volume is 1 cm3. • A 2-cm cube of the same material has a crosssectional area of 4 cm2 and a volume of 8 cm3. • What about a 5-cm cube? – Volume = ________ – Cross sectional area = __________ Scaling How scaling affects strength. • Compare the thick legs of large animals to those of small animals: an elephant and a deer, or a tarantula and a daddy longlegs. Scaling • Surface area to volume ratio – Smaller objects have more surface area per kilogram. • Cooling occurs at the surface… So crushed ice cools a drink faster than an ice cube! (The crushed ice presents more surface area) • Steel wool rusts faster than a solid piece of steel. • Chunks of coal burn, while coal dust explodes! • Thin French fries cook faster in oil than fat fries. • Flat burgers cook faster than meatballs. Scaling • Scaling and living organisms – The big ears of an elephant are not for hearing, but for cooling! – If an elephant did not have large ears, it would not have enough surface area to cool its huge mass. Liquids Liquids • Liquid pressure depends on depth (not on volume). Soda Bottle Demo Liquid Pressure think! A brick mason wishes to mark the back of a building at the exact height of bricks already laid at the front of the building. How can he measure the same height using only a clear garden hose and water? Buoyancy • Buoyancy: Apparent loss of weight of objects when submerged in a liquid. Buoyancy • The upward forces against the bottom of a submerged object are greater than the downward forces against the top. There is a net upward force, the buoyant force. Bouyancy • When an object is submerged, it displaces a volume of water equal to the volume of the object itself. Archimedes Principle • States… “the buoyant force on an immersed object is equal to the weight of the fluid it displaces” The weight of the fluid displaced is = to the buoyant force on the rock Archimedes Principle • A brick weighs less in water than it does in air. Archimedes Principle think! A block is held suspended beneath the water in the three positions, A, B, and C. In which position is the buoyant force on it greatest? Answer: The buoyant force is the same at all three positions, because the amount of water displaced is the same in A, B, and C. Does It Sink, or Does It Float? • Sinking and floating can be summed up in 3 simple rules. – An object more dense than the fluid in which it is immersed sinks. – An object less dense than the fluid in which it is immersed floats. – An object with density equal to the density of the fluid in which it is immersed neither sinks nor floats. Does it Sink or Float? • The wood floats because it is less dense than water. • The rock sinks because it is denser than water. • The fish neither rises nor sinks because it has the same density as water. Flotation • How does a ship made of iron float? – Iron is nearly 8 times more dense than water • The answer is in the shape of the hull! Flotation • The iron bowl still weighs 1 ton but if you lower the bowl into a body of water, it displaces a greater volume of water. • The deeper the bowl is immersed, the more water is displaced and the greater is the buoyant force exerted on the bowl. • When the weight of the displaced water equals the weight of the bowl, it will sink no farther. • The buoyant force now equals the weight of the bowl. Flotation A solid iron block sinks, while the same block shaped to displace more water floats. Flotation • Every ship must be designed to displace a weight of water equal to its own weight. • A 10,000-ton ship must be built wide enough to displace 10,000 tons of water before it sinks too deep below the surface. Flotation • The same ship is shown empty and loaded. The weight of the ship’s load equals the weight of extra water displaced. Pascal’s Principle • Describes how changes in a pressure are transmitted in a fluid. • The principle behind all hydraulic systems. Pascal’s Principle • A 1-N load on the left piston will support 50N load on the right piston. • The piston on the left has an area of 1cm2. • The piston on the right has an area of 50cm2. Pascal’s Principle • The automobile lift is in many service stations. • Whatever air pressure the compressor supplies to the reservoir, is transmitted through the oil to the piston that raises the car. Gases Chapter 20 Atmospheric Pressure • Caused by the weight of the air above us. – When a Boeing 777 is fully pressurized approximately 1000 kg is added to it’s mass. Measuring Air Pressure • An instrument used for measuring the pressure of the atmosphere is called a barometer. – In a simple mercury barometer, a glass tube (longer than 76 cm) closed at one end, is filled with mercury and tipped upside down in a dish of mercury. – The mercury in the tube runs out of the submerged open bottom until the level falls to about 76 cm. Air Pressure • You cannot drink soda through the straw unless the atmosphere exerts a pressure on the surrounding liquid. Measuring Air Pressure • An aneroid barometer is an instrument that measures variations in atmospheric pressure without a liquid. • Since atmospheric pressure decreases with increasing altitude, a barometer can be used to determine elevation. Boyles Law • “The product of pressure and volume for a given mass of gas is a constant as long as the temperature does not change” Boyles Law Describes the relationship between the pressure and volume of a gas. P1V1 = P2V2 P1 and V1 represent the original pressure and volume P2 and V2 represent the second, or final, pressure and volume Boyles Law think! If you squeeze a balloon to one third its volume, by how much will the pressure inside increase? Bernoulli’s Principle • In it’s simplest form states… “when the speed of a fluid increases, pressure in the fluid decreases” Water flows through the pipe below. Describe the velocity through the wide portion vs. the narrow portion. How does this relate to pressure within the pipe? Application of Bernoulli’s Principle • In high winds, air pressure above a roof can drastically decrease. Application of Bernoulli’s Principle • Throwing a curve ball. Applications of Bernoulli’s Principle • Passing Boats run the risk of a sideways collision. • Try this experiment in your sink! Application of Bernoulli’s Principle …the shape of an airplane’s wing! • Due to the shape of airplane wings, air passes somewhat faster over the top surface of the wing than beneath the lower surface. • Pressure above the wing is less than pressure below the wing. • Lift is the upward force created by the difference between the air pressure above and below the wing.