"korobu　ころぶ（転ぶ）" ：to stumble on something (i.e. a stone) and fall to the ground fall over a stone = 石につまずいて転ぶ fall over on the street = 道で転ぶ "ochiru　おちる（落ちる）"：to fall from high places (i.e. a roof, a ladder, a bed) 　　　　　　　　　　　　　　　　to drop into somewhere under the ground (i.e. hole, pitfall) 　fall from a ladder：はしごから落ちる fall off the bed：ベッドから落ちる 　drop into a pitfall：落とし穴に落ちる "おちる" has a lot of meaning other than those above. ---------------------- My English is still poor. Can you understand my answer? Hope this will help :)

ochiru = downward falling korobu = tumbling falling http://jisho.org/words?jap=ochiru&eng=&dict=edict http://jisho.org/words/?jap=korobu&eng=&dict=edict There you will find example sentences that highlight the differences and similarities.