We are two girls from Norway and we just learned about German "alternation spread prepositions" or "Wechselpräpositionen". What I mean is those prepositions that sometimes controls dative and sometimes accusatives, for example "an, auf, hinter" etc. My question is; we learned that if the subject moves in a determined, limited area, it will be dative. But when we tried to use dative for something that moved in a determined area such as the country, or even the globe, our teacher said the rule did not count here, because the determined area was to big. Therefore, we wonder if there is any limit for when this rule counts and not. In that case, how large is the limit? Thank you.
There are exactly nine Wechselpräpositionen, an, auf, hinter, neben, in, über, unter, vor and zwischen. These mean a different thing when used either with dative or accusative.
What's right is accusative is connected to movement while dative is connected to a location, but this is only a rule of thumb. What your teacher meant is most likely the following:
Ich ging an den Strand. (an+accusative)
I walked to the beach.
Ich ging am Strand. (an+dative)
I walked on the beach.
In both cases, you walk, clearly a movement. In the first sentence, der Strand is a direction you are heading to, while in the second sentence, der Strand is a place where you do something.
Be careful, however, because the verb or object may command either a direction or a place, so it's not always intuitive:
Er sprang über den Zaun. (über+accusative)
You may think you need a dative here because der Zaun is the place where the jump happens, but it needs to be a direction, because a Zaun is a thing crossed by an action.
Sie kommt am Bahnhof an. (an+dative)
The verb ankommen requires a place, not a direction, though you may see ankommen as a movement.