- It formed inside him an ambition to teach his students all the more.
- It formed an ambition to teach his students all the more inside him.
- He kept in the book bag an apple. (awkward or marked)
- He kept an apple in the book bag.
The differing acceptability of these examples is due to a phenomenon known as HEAVY NOUN PHRASE SHIFT. It gives us the illusion that we are able to move the preposition phrases in the sentence around, but really what we are moving is not the preposition phrases; it's the noun phrase ambition to teach his students all the more on the one hand and an apple on the other.
We term a noun phrase as heavy when it is long. You'll notice that the noun phrase ambition to teach his students all the more is very heavy. The noun phrase an apple is, of course, rather light. When a noun phrase is the Direct Object in a sentence, it normally occurs directly after the verb (or if there is an Indirect Object, after the Indirect Object). If there are other phrases, for example locative or temporal Adjuncts or Complements, we cannot just switch their positions willy-nilly, or the sentence will be deemed ungrammatical:
- *I met in the office canteen just now Bob.
In the sentence above I put the Direct object Bob after the Adjuncts (or "adverbial") in the office canteen and just now. Because Bob doesn't directly follow the verb, the sentence would be regarded as ungrammatical. However! If we make the Direct Object very heavy, in other words if we make it long we can move the Direct Object to the end of the sentence, no problem:
- I met in the office canteen just now that guy Bob who you bumped into the other day.
Now that the Direct Object is a ten word noun phrase, that guy Bob who you bumped into the other day, we can move it right over all the other phrases to the end of the sentence. It is perfectly grammatical.
In the Original Poster's examples (1) is fine because the noun phrase an ambition to teach his students all the more is heavy enough to move to the end of the sentence past the preposition phrase inside him. But in the Original Poster's third example, an apple is too short to justify moving to the end of the sentence. It needs come after the verb and before the preposition phrase in the book bag to sound natural. But this has nothing to do with the preposition phrase, it's just because the noun phrase, the Direct Object, is very light. The feeling that we're moving the preposition phrase is a kind of illusion.