Matter and Physics

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Matter and Physics
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Classification of Matter

• Four States of Matter
• Solid rigid - fixed volume and shape
• Liquid definite volume but assumes the shape of
  its container
• Gas no fixed volume or shape - assumes the
  shape of its container
• Plasma ionized gas atoms--in stars, in welders,
  and even fire

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Types of Solids

• Crystalline Solids highly regular arrangement
  of their components table salt (NaCl), pyrite
  (FeS2).
• Amorphous solids considerable disorder in
  their structures (glass).

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Solids

• Crystal Structure
• Crystals are a regular arrangement of atoms of a
  solid
• Regular geometric shape
• Regular spacing between

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Solids

• Discovered. by X-rays that pattern was regular
• X-rays through crystal bend around atoms
• Ionic and metal crystals are simple
• Organic crystals much more complex

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Elasticity

• Stretching ability plus ability to return to
  its original shape
• Materials which deform and do not return to shape
  are inelastic

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Elasticity

• Stretch of a spring is directly proportional to
  applied Hookes Law - F kx
• There is a limit to which stretched will return -
  elastic limit - why a Slinky must be replaced

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Quantities of Elasticity

• Three types of deformation occur in solids
• 1. Tensile stress has to do with change in
  length -- measured by Youngs modulus
• 2. Shear stress has to do with changing shape
  without volume measured by the shear modulus
• 3. Volume stress has to do with resistance to
  compressibility measured by the bulk modulus

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Compression and Stretching

• In solids, like steel, placed horizontally top
  and bottom behave opposite
• There is always a point between with no stretch
  or compression - a neutral layer

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Compression and Stretching

• I -beam girders take advantage of this -
  neutral layer in I area in center much less
  weight for same strength

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Density

• Lightness or heaviness
• Does not change if material is broken
• Does change if material is compressed

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Density

• r m / V (mass divided by volumekg/ m3)
• Determined by mass of atoms and their spacing
  Osmium most dense element due to close spacing
• Density of water 1 g/cm3 by definition (1000 kg
  / m3)
• Weight density is similar, weight / volume, mg
  / V, or r g
• Specific gravity normally has to do with density
  of liquids, and is the ratio of the density of a
  substance to that of water

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Scaling

• Relationship between size and, weight, strength,
  and surface area
• Ant is much stronger for its size than an
  elephant
• Elephant size ant would be very weak - it isnt
  built for increased size
• Objects which are larger are much heavier than
  stronger
• Strength depends on the cross section area
• Weight depends on volume
• Volume (cubic measure) grows faster than area
  (square measure)
• Area 22 4
• Volume 23 8
• Density makes mass and volume proportional

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Scaling

• Large animals must have greater area to hold
  their greater weight -elephant vs. deer, ant vs.
  tarantula
• King Kong could not be strong due to scaling -
  science fiction

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Scaling

• Surface area grows slower than volume also
• Elephant ears for cooling make up for lack of
  elephant surface area
• Cells must divide to increase surface area for
  life
• Surface area makes small animals fall without
  damage
• Chemical reactions take place faster with more
  surface area

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Liquids

• Pressure in liquids
• Pressure is force per unit area P F / A , units
  are Pascals, equal to 1 Newton per meter squared
• For liquids, pressure on bottom of container
  equals weight density times depth of liquid or r
  g h

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Liquids

• The pressure is same for the same liquid at the
  same depth no matter the volume
• At 5 feet in a small lake is same as at 5 feet
  in the ocean
• Depth causes pressure to be greater in a deep
  pool vs. a shallow one
• A container with holes filled with liquid, liquid
  sprays farthest from the lowest hole due to
  higher pressure

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Pascal's Principle

• Changes in pressure at any point in an enclosed
  fluid at rest are transmitted to all parts and
  act in all directions
• This principle is used in hydraulic equipment
  everywhere
• pressure in
  pressure out

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Pascal's Principle

• Can be used to increase force by same simple
  machine principle 1N moves greater distance to
  induce 50 N output
• Lift for cars in gas station or elevators in
  buildings can be done by this effect

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Homework

• P 298 9, 10, 11, 12

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Atmospheric Pressure

• Caused by weight of air pressing on us
• Weight 1.2 kg/m3 - a lot if you have a lot of
  air
• We dont feel the weight because we are
  surrounded by air

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Atmospheric Pressure

• Pressure calculates to 10 N/cm2
• Converting this, it becomes
• 100,000 N/m2
• Average atmospheric pressure 101.3 kPa at sea
  level
• Pressure varies and brings weather changes

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Mercury Barometers

• Mercury barometer uses a column of mercury to
  measure pressuredeveloped by Torricelli
• Average mercury reading is 76 cm or 760 mmHg
• Size of the tube is immaterial - always goes to
  the same height

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Mercury Barometers

• Works on same principle as straw - air pushes
  down on liquid and pushes up into straw or tube
• Trying to suck liquid from a sealed container
  would not be possible due to lack of atmospheric
  pressure
• Atmospheric pressure limits how deep a well can
  be which uses a vacuum pump 10.3 m

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Aneroid Barometers

• Cans can be crushed by atmospheric pressure if
  air is driven out
• Aneroid uses a metal box with a partial vacuum
• Air pressure varies size of box, measured with
  spring and lever system
• Can be used to measure altitude if calibrated

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Buoyancy

• Objects underwater are easier to lift than above
  surface
• Water is exerting an upward force called buoyant
  force
• Caused by water pressure greater beneath object
  than above it
• Floating occurs due to this force
• If weight gt buoyant force - object sinks
• If weight buoyant force object remains at any
  level (fish)
• If weight lt buoyant force - object floats

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Buoyancy

• Water is displaced by a submerged object
• Amount displaced volume of object
• Use this to find volume of irregular objects

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Buoyancy

• Archimedes Principle
• Immersed object is buoyed up by force equal to
  displaced
• True for both liquids and gases - both are fluid
• Immersed either totally or partially submerged
• Causes apparent weight difference
• 300g block 3N Displaces 2N if submerged
• 3N - 2N 1N apparent weight in liquid

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Buoyancy

• Archimedes principle depends on volume rather
  than weight of object -density of object
• Submarines take water in or let it out
• Fish change size of air sac
• Crocodiles swallow stones to get lower

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Floatation

• Ship can be made of iron or even concrete and
  still float.

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Floatation

• Shape causes larger volume and more buoyant
  force.
• Floating object displaces fluid equal to its own
  weight.

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Buoyancy

• Archimedes principle applies in gases
• Object buoyed up by force equal to weight of air
  displaced
• Airships (Goodyear, Fuji) float due to this
  principle

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Homework

• P 299ff 17, 20, 21, 25, 27, 29

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Behavior of Moving Fluids

• Pressure Differences Cause Motion
• Air flows from areas of high to low pressure
• This causes winds and storms
• Tornadoes, hurricanes have very low pressure and
  thus high winds

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Fluid Flow

• Fluid flow is laminar or streamline if every
  particle of that fluid moves in a smooth parallel
  pathway.
• Fluid flow that is not regular, due to too high a
  velocity or sudden changes in velocity, is called
  turbulent and the motions of the fluid are called
  eddy currents.
• In addition, viscosity, the internal friction of
  a fluid, has an effect on flow as well. Gasoline,
  with low viscosity, can flow much faster than
  honey without turbulence.

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Equation of Continuity

• In a streamline which is changing cross-
  sectional area, the mass of fluid transferred
  along the streamline does not change in a laminar
  stream. This means that the flow time also does
  not change, and thus r A1v1 r A2v2 implying
  that the velocity must change if the area changes
  in inverse relation. This equation simplifies to
  A1v1 A2v2 and is called the equation of
  continuity.

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Bernoullis Principle

• Greater the speed of flow, less pressure
  perpendicular to flow
• Kinetic - flow motion
• Potential - pressure on sides
• Gravitational Potential - due to altitude
• Sum of these three is constant in a steady fluid
  flow
• Pressure here is not that of the fluid against an
  object, only against walls of container

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Bernoullis Principle

• If flow speed is too great, turbulence forms
• Flow begins to follow curling path or Eddy
• Bernoullis principle holds only to straight flow

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Bernoullis Equation

• Through a series of manipulations, Bernoulli
  showed that the sum of the pressure, the kinetic
  energy per unit volume, and the potential energy
  per unit volume is constant. This is expressed
  as
• P ½ rv2 rgy constant
• This is often used in cases where potential
  energy does not change, so that the equation can
  be rearranged to
• P1 ½ rv12 P2 ½ rv22 or DP ½ rv22 -½ rv12
  
• With this equation, the pressure for lift on an
  airplane wing can be calculated if both
  velocities are known. Then the lift can be
  calculated by multiplying pressure x area.

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Applications of Bernoulli

• Flight - wings designed for faster airflow on
  top, causing less pressure than beneath
• Difference in pressure causes lift similar to
  buoyant force in liquids
• When lift weight, flight is possible
• Lift depends on size of wing and speed of craft
• Low speed requires large wings
• High speed can not have very large wings

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Applications of Bernoulli

• Curve ball in sports caused by spin
• Spin produces unequal pressure
• Pressure difference causes force in various
  directions

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Homework

• P 301ff 31, 33, 34, 61, 62, 70