Describe factors that increase or decrease friction and drag, and use stopping-distance data to compare surfaces.
Friction is a force between two surfaces in contact that resists motion, acting opposite to the sliding direction. Rougher surfaces create more friction, and pressing surfaces together harder also increases it.
Drag is friction's cousin, between an object and a fluid (air or water). Drag increases sharply with speed and with the surface area facing the motion -- a parachute's huge open surface creates enormous drag, while a narrow diver's body creates very little.
Mastery looks like: They predict which of two surfaces or shapes experiences more friction or drag and explain why, using stopping-distance evidence when available.
Common stumbles: Treating friction and drag as identical; assuming heavier objects always slide farther, when more weight usually means more friction and a shorter slide.