The importance of the definition of weight

Presented by the Newton definition of weight that identifies the weight with the force of gravity exerted on the body, at the ninth grade, results in miss- conceptions: gravity stops at the end of the atmosphere and needs air for its activity, gravitation is unique to earth does not act in other locations such as on the moon or Mars. There is no gravity in space. An astronaut orbiting around the earth is not affected by gravity. When these findings were researched at high school: at grades eleven and twelve, among students and teachers the same miss- conceptions were observed. No reduction of them was found. Differentiation between apparent and real weight did not improve the results. Facing these results it was suggested to change the definition of weight and choose the one that young pupils use: weight is the force exerted by the body on the hand or any other support including the scale. This definition assumes that free falling bodies have no weight. In this way continuity is achieved both with young pupils' definition and the assumption made in general relativity that falling bodies have no weight. Two research works were made using this definition and resulted with a significant reduction of the miss-conception and even vanishing of some of them. This result was achieved using two different instruction methods.