English: The diagramm depicts Galileo's thought experiment on free falling bodies. Suppose you have two objects, one heavier (b) than the other (a). Suppose the heavier object falls faster. When you put the lighter object under the heavier object (c), the lighter object should slow down the heavier object. On the other hand gluing together both objects results in an heavier object (c), which should fall even faster than (b). The contradiction proves (by reductio ad absurdum) that the assumption must be false.