Phy 102: Fundamentals of Physics II Chapter 12 Lecture Notes

English chemist, mathematician, physicist, and inventor (the spiral spring) England’s 1 st experimental scientist. Founder of many scientific fields, including: –Microscopy- Microbiology –Meteorology- geology –Earth sciences Robert Hooke ( ) Gained acclaim for writing the 1 st 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

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

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/m 3 –Other: g/cm 3 (or g/mL), kg/L, g/L

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 (  x): F ~  x {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)

The Soloflex

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)

Arches An inexpensive restaurant specializing in fried foods

Scaling An object’s strength is proportional to its cross-sectional area (A): Strength ~ A (measured in m 2 or cm 2 ) An object’s mass is proportional to its volume (V): Weight ~ V (in m 3 or cm 3 ) 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)