Phy 102: Fundamentals of Physics II

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Phy 102 Fundamentals of Physics II

• Chapter 12 Lecture Notes

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Robert Hooke (1635-1702)

• English chemist, mathematician,physicist, and
  inventor (the spiral spring)
• Englands 1st experimental scientist.
• Founder of many scientific fields, including
• Microscopy - Microbiology
• Meteorology - geology
• Earth sciences

• Gained acclaim for writing the 1st microscopy
  textbook
• Known for his creating brilliant ideas but not
  following them up to develop complete theories
• Contemporary ( scientific enemy!) of Isaac
  Newton
• Hooke claimed Newton stole many of his ideas
  including his theory of universal gravitation and
  a particle theory of optics
• Hooke was known for his frequent and bitter
  disputes with fellow scientists

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Solids

• Substance with definite shape definite volume
• Classifications of solids
• Crystalline (regular)
• Amorphous (irregular)
• Types of solids
• Ionic
• Covalent
• Metallic
• Van der Waals

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Density

• A physical property of matter
• The relationship between a substances mass and
  the volume of space it occupies
• Depends on
• Mass of the atoms/molecules
• How tightly the atoms are packed together
• To calculate density
• Density mass/volume
• or
• D m/V
• Units are
• SI kg/m3
• Other g/cm3 (or g/mL), kg/L, g/L

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Elasticity

• Elastic materials have 2 characteristics
• They change shape when a deforming force acts on
  an object (e.g. compress or stretch)
• They return to the original shape when the
  deforming force is removed
• The force (F) required to deform an elastic
  material is proportional to the amount of
  deformation the object experiences (Dx)
• F Dx This is called Hookes Law
• Elastic materials can be stretched/compressed
  past a point (called the elastic limit) beyond
  which Hookes Law no longer applies ( they stay
  permanently deformed)

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The Soloflex
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Tension Compression

• Something pulled on (stretched) is referred to as
  being under tension
• Something pushed in is in compression
• When something is bent
• the outside part of it is in tension
• the inner part is in compression
• Somewhere between these regions is an interface
  called the neutral layer (where neither tension
  nor compression occurs)
• Steel girders are designed in I shapes to that
  maximum material is at tension/compression
  regions minimal material is located at the
  neutral layer (to maximize stretch minimize
  weight)

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Arches

• An inexpensive restaurant specializing
• in fried foods

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Scaling

• An objects strength is proportional to its
  cross-sectional area (A)
• Strength A (measured in m2 or cm2)
• An objects mass is proportional to its volume
  (V)
• Weight V (in m3 or cm3)
• As objects increase in size, volume weight
  increase faster than cross-sectional area
  strength
• This results in disproportionately larger support
  features (such as legs)
• Lighter animals tend to have thin legs (spiders,
  deer, etc.)
• Heavier animals tend to have thick legs (rhinos,
  elephants, hippos)