Equilibrium: no net force, no acceleration, constant velocity or at rest, forces form a closed figure. Concurrent vectors: placed tail-to-tail component vectors: must be head-to-tail to find resultant. Resultant force = fnet : head-to-head and tail-to-tail with components. Range of possible resultants: maximum = sum of vectors minimum = difference of vectors. Box on a hill in equilibrium: mgsin = ff or fa or ft and mgcos = fn. Mass (m): = inertia, amount of matter, constant from place to place, units: kg. Weight (fg): = force of gravity, changes from place to place, units: n formula: fg = mg. Triangle rule sum of any 2 sides third side for forces to be in equilibrium. Fn f = m g sin f =mgcos . Gm/r: acceleration due to gravity, units: m/s , formula: g = 2 2: gravitational field strength, units: n/kg, formula: g = fg/m.