Drop off is someplace were you can leave things ... I distributed 10 questionnaires to 2 different drop-offs (It could also mean a downward slope) a fall off in sales to fall down on a job Fall down: Fail in meeting expectation ... He fell down on his job Fall off: A decrease: Stock prices have fallen off

Yes, there are some differences. I dropped off my clothes at the dry cleaners today I drop them off every week and pick them up when they are ready. Be careful, or you may fall off the chair The floor is wet so be careful that you don't slip and fall down

Because phrasal verbs can have very different meanings depending on the context, I'll assume you mean an object/person moving downwards from a height. "drop off" = the focus is on the beginning of the fall. You'll normally tell us where from: drop off a table, drop off a cliff, drop off the edge... "fall off" = very similar to drop off, except this suggests an accident. "fall down" = the focus is on the end of the fall, ie. the ground. The object/person was not caught or stopped during the fall. Normally the fall begins from a natural standing position (eg. of a person, or a building) and not from a higher place.