Can someone give me an example of
...how the accusative case can be used to express direction? I found this on Wikipedia, and I can't picture how that works.
"Direction of motion can be expressed either by the accusative case, or by the preposition al (to) with the nominative."
EDIT: Never mind. I find the explanation on Lernu. I'll post it below for you all. :)
Direction by -n After prepositions, use the basic word form without -n. pri la knabo - about the boy en la domoj - in the houses al la urbo - to the city
After prepositions which do not indicate movement, but do indicate a place, you use -n to show motion to that location. Hundo saltas sur la tablo. - A dog jumps on the table. Hundo saltas sur la tablon. - A dog jumps onto the table. Mi iras en la domo. - I go in the house. Mi iras en la domon. - I go into the house.
La kuniklo saltas sur la elefanton. La kuniklo saltas sur la elefanto. -n works the same way after adverbs which indicate location. hejme - at home | hejmen - [to] home urbe - in the city | urben - to the city kie - where | kien - to where tie - there | tien - to there
La kato saltas sur la tablo = the cat is on the table and jumps on it. (La kato saltas surtable)
La kato saltas sur la tablon = the cat is not yet on the table but jumps onto it. (La kato saltas surtablen)
Mi iras en la urbo = I wander in the town.
Mi iras en la urbon = I was in the country side and go into the town.
Mi iras al la urbo = I go to the town. NEVER put an accusative after AL.
Is there a rule regarding why the accusative N changes the meaning of the preposition? For example, in your first sentence "sur" means "on top of" and in the second sentence it means "onto".
It's what is sometimes called accusative of movement. Just to show the goal: Mi metas mian poŝtelefonon (object) en mian poŝon (end goal of the moving, transfer, shifting). Mi tradukas la libron (object) Esperanten (goal accusative).
I think it means like direction of the sentence. There are three things in a sentence; a subject, an object, and a verb. The subject does the verb to the object, and therefore the object gets the Accusative ending. For example: "Mi trinkas lakton" (I drink milk) In this sentance direction is shown in that the subject, mi, drinks the milk.
So direction in the way it's worded? So a different direction might be "Lakton mi trinkas"?
"Mi trinkas lakton" and "Lakton mi trinkas" have the same meaning, just the emphasis in on "mi" in the first sentence and "lakton" on the second. the -n ending has actually at least 2 meanings, the accusative like in these examples and for indicating movement in some cases like in the examples of balou67 .