This document discusses forces and motion. It defines key terms like force, net force, balanced and unbalanced forces. It explains that an object's motion can only be determined relative to another object used as a reference point. Forces can be added or subtracted depending on whether they act in the same or opposite directions. A net force causes an object to change its motion, such as starting to move, stopping, or changing direction. Balanced forces in opposite directions do not change an object's motion.