phy53 lect		dr brown		26 oct 2010

prelecture conversation -- cars, manual transmission, hybrids, gas mileage

exam comments -- don't try to memorize "bank" of problems -- learn to "think physics"

torque...

theorems about torque for certain combinations

"coupled forces" --   torque indepen of coordinates

arbitrary pair of forces --  torque decomposes into orbital and spin effect on angular momentum

if total force and torque are zero in one frame with pivot at origin - then zero in all inertial frames 

add conditions - at rest and not rotating == static equilibrium

examples w/ static equilib

1. plank (scaffolding) on two stands and painter some distance from one end

2. tipping problem -- cube on inclined plane

    consider tipping vs sliding angle 

3. piano up the stairs with guy at each end

4. wheel at curb and horizontal force applied at C-of-Mass

5. string and some angle holding horizontal rod up against wall