Dr. Brown    		Phy53 Lect. 11:40-12:55 		9 September 2010

two force laws ... friction and drag
1st -- motion in accel frame:  in rocket stand on scale [use N2 -- no need for psuedo force ; 1D]
                               in rail car w/ hanging mass ; 2D


friction -- 
	atomic view of matter -- dipole/weak bond between two surfaces -- "sticky";  zoom in on surface = rough
	break weak bonds and "lift" enough to slide

static friction  F_s <:= \mu_s N
       once moving
kinetic friction  F_k = \mu_k N

opposes relative motion of surfaces

inclined plane w/ friction

      \theta_max



drag forces --
	spherical object in "fluid"  -- moving molecules...pressure; no net force when at rest -- but when moving with some velocity -- pressure bigger on side toward which 'tis moving -- opposes motion 
	for slow moving, laminar flow, round ...objects;  
	F_d = -b v^n    [b=drag coefficient, n=index  ~1 when slow  ..~2 when fast;   we will use 1 !]

problem  -- dropping UNC ram from helicopter into large bucket of Duke blue paint => linear, first order, inhomogenous ODE -- exponential...seperable [terminal velocity]