a) Box ist in Ruhe, da Mensch nicht dran zieht und Gewichtskraft und Normalkraft sich die Waage halten. b) Mensch zieht, aber Zugkraft kann Haftreibung nicht überwinden c) Zwei Menschen ziehen (doppelte Zugkraft) und die gemeinsame Zugkraft überwindet die Haftreibung. d) Box ist nun in Bewegung, die Reibungskraft geringer.

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