Momentum, rotation, oscillations and fluids

This topic covers four AP Physics 1 ideas that often catch out students who are comfortable with basic forces and energy. It begins with momentum. Momentum is a vector, so you choose one direction as positive and give anything moving the other way a negative velocity before adding. Next is rolling. A ball rolling down a ramp both moves and spins, so part of its energy becomes rotational kinetic energy, and it reaches the bottom slower than a frictionless block would. The third page is the pendulum. Its period depends on length and gravity, not on the mass of the bob, which surprises a lot of people. A mass on a spring is different, because there the mass does matter. The last page is buoyancy. The buoyant force equals the weight of fluid displaced, so a floating object only counts the volume below the surface. For every question here, sketch the situation and label directions first.