Matter and Physics

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Matter and Physics
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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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Density

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

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Density

• D m/v
• Determined by mass of atoms and their spacing
  Osmium most dense element due to close spacing
• Density of water 1 g/cm3 by definition
• Weight density is similar, weight / volume

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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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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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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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Homework

• RQ 2, 4, 7, 8, 11, 12, 18, 19
• TE 3, 6, 9, 10

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Liquids

• Pressure in liquids
• Pressure is force per unit area
• For liquids, pressure on bottom of container
  equals weight density times depth of liquid

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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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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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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

• RQ 1, 2, 3, 6, 12, 13, 14, 15
• TE 2, 3, 5, 6, 7, 10