The Buoyancy Scale



A metal rod and a styrofoam orb are put at both ends of a balance scale. Both seem equal in mass. If the setup is exposed to vacuum, the bigger ball tends downwards.

In order to understand this experiment, the students need to trail the buoyancy (in air). Independently, they conclude with the help of school books or with the assistance of their supervisors, that if mass is to be measured properly, the weighing has to be done in vacuum. (The mass of the styrofoam orb in our case is 0,2 g larger than the one of the metal rod).