phy53 lect dr. brown 16 november 2010 curve balls -- baseball
discussion -- golf balls...dimpled surface; compare to ping pong
ball leading to Young's Modulus atoms modeled like connected by
springs [discussion of similarity -- Leonard-Jones potential --
consider Taylor series expansion about the minimum] single
chain; two chains; block of material with cross sectional
area... F_{restoring} = - Y A/L \Delta L = -"k_eff" \Delta L Y =
young's modulus = stress over strain = (F/A)/(\Delta L /L)
explains linear response limit, elastic limit[permanent
deformation] and fracture limit Another material response --
push rectanglular cross section at top -- shear stress and
strain Shear modulus = shear stress / shear strain = (F/A) /
(\Delta x /L) finally -- "Bulk modulus" increase pressure --
response is change in volume large bulk modulus => low
compressibility We can really understand springs now and where,
from microscopic view of matter, Hooke's Law comes from-- so,
solve -- mass on a spring F_x = -kx = m a = m \fr