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Phy 102: Fundamentals of Physics II

Phy 102: Fundamentals of Physics II. Chapter 12 Lecture Notes. Robert Hooke (1635-1702). English chemist, mathematician, physicist, and inventor (the spiral spring) England’s 1 st experimental scientist. Founder of many scientific fields, including: Microscopy - Microbiology

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Phy 102: Fundamentals of Physics II

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  1. Phy 102: Fundamentals of Physics II Chapter 12 Lecture Notes

  2. Robert Hooke (1635-1702) • English chemist, mathematician,physicist, and inventor (the spiral spring) • England’s 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

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

  4. Density • A physical property of matter • The relationship between a substance’s 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

  5. 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 Hooke’s Law} • Elastic materials can be stretched/compressed past a point (called the elastic limit) beyond which Hooke’s Law no longer applies (& they stay permanently deformed)

  6. The Soloflex

  7. 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)

  8. Arches An inexpensive restaurant specializing in fried foods

  9. Scaling • An object’s strength is proportional to its cross-sectional area (A): Strength ~ A (measured in m2 or cm2) • An object’s 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)

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