The concept of a container is tangible, not abstract.
We are representing physical Containers by delimiting Boundaries and basic facts by empty containers.
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physical | BrE ˈfɪzɪkl, AmE ˈfɪzək(ə)l | A adjective 1 (material) physisch ‹Gewalt› stofflich, dinglich ‹Welt, Universum› 2 (of physics) physikalisch ▸ it's a physical impossibility (figurative) es ist absolut unmöglich 3 (bodily) körperlich physisch ▸ you need to take more physical exercise du brauchst mehr Bewegung ▸ physical check-up or examination ärztliche Untersuchung ▸ get/be physical (informal) rabiat werden/sein 4 (carnal, sensual) körperlich ‹Liebe› sinnlich ‹Person, Ausstrahlung› B noun ärztliche [Vorsorge]untersuchung (for joining the army) Musterung (Fem.)