Safety first -- Weighing in -- More weighing in -- Weight and position -- Gravity and different weights -- Measuring weight: a "spring" scale -- Weight and friction -- Becoming weightless -- Seesaws, weights, distances, and levers -- Levers to lift weights -- An inclined plane -- Measuring weight with a balance -- Can you weigh air? -- Weighing air -- Some effects of air's weight -- Defying gravity -- Defying gravity again -- Using a siphon to defy gravity -- Forces other than gravity.