Reviewed homework.  Considered a number of vector addition problems. Examples included adding displacements and adding forces.

Re-reviewed homework to discuss why in an expressed such as 0.2 cos( 0.3 + 0.4 t ) that we should evaluate the expression using the radian mode of the calculator and not the degree mode.  We further derived an expression (v²/r) for the magnitude of the centripetal acceleration.  We discussed that having an acceleration meant there is a change in velocity, but since velocity is a vector that change might be in the magnitude, the direction or both. We then examined the forces acting on a freely falling object (gravity), an object sitting still on a horizontal plane (gravity and normal), and an object sliding down an incline (gravity, normal and possibly friction.)