W nowym samochodzie fotel jest wygodniejszy, ale hamulec działa inaczej niż w starym.

Because w can take different cases depending on meaning.

• When w means in/inside as a location, it takes the locative case.
• Here we are talking about something located in the new car, so we use the locative: w nowym samochodzie.

If there were movement into something, Polish would usually use w + accusative, for example: Wsiadłem w nowy samochód.

So in this sentence, w nowym samochodzie is correct because it describes location, not motion.

Those are locative singular forms.

• nowy → nowym
• stary → starym
• samochód → samochodzie

The adjective has to agree with the noun in gender, number, and case, so since samochód is masculine singular and is in the locative, the adjective also appears in masculine singular locative: nowym samochodzie.

The noun samochód changes to samochodzie in the locative singular. That kind of stem change is normal in Polish declension.

The noun is omitted because it is obvious from context.

w starym means something like in the old one, where one refers to samochodzie. Polish often leaves out a noun if it has already been mentioned and can be easily understood.

So:

• w nowym samochodzie
• w starym = w starym samochodzie

The adjective starym still stays in the locative because the hidden noun is still understood to be in the locative.

Because they are the subjects of their clauses, so they are in the nominative case.

• fotel jest wygodniejszy
• hamulec działa inaczej

In Polish, the subject of a sentence is normally in the nominative. The dictionary form of a noun is usually the nominative singular, which is why these words look unchanged here.

Wygodniejszy is the comparative form of wygodny.

• wygodny = comfortable
• wygodniejszy = more comfortable

Polish often forms comparatives with endings like -szy, -iejszy, or -niejszy. In this case, the comparative is built as wygodniejszy.

You can also sometimes use bardziej wygodny, and it would be understandable, but the one-word comparative wygodniejszy is the more natural and standard choice here.

Because the sentence is describing two different kinds of things:

• fotel jest wygodniejszy describes a quality of the seat, so Polish uses być
  • adjective.
• hamulec działa inaczej describes how the brake functions, so Polish uses a verb of action plus an adverb.

So:

• wygodniejszy is an adjective describing fotel
• inaczej is an adverb describing działa

That difference is very natural in Polish.

Inaczej is an adverb meaning differently. It modifies the verb działa.

So hamulec działa inaczej means the brake works/functions differently.

This is a common Polish pattern:

• robić coś inaczej = to do something differently
• działać inaczej = to work differently
• wyglądać inaczej = to look different

Niż is used for comparison, especially after comparatives or words implying difference.

Here it links the idea differently with the thing being compared:

• inaczej niż w starym

That is basically differently than in the old one.

Polish also uses niż after forms like:

• lepszy niż
• większy niż
• szybciej niż

So in this sentence, niż introduces the comparison point.

Not naturally in this exact sentence.

With simple adjective comparisons, Polish often allows both patterns:

• większy niż tamten
• większy od tamtego

But here the comparison is built around inaczej and an elliptical phrase w starym, so niż is the normal choice:

• działa inaczej niż w starym

Using od here would sound wrong or at least very unnatural.

Because ale is a coordinating conjunction meaning but, and in Polish it is normally preceded by a comma when it joins two clauses.

So the structure is:

• W nowym samochodzie fotel jest wygodniejszy, ale hamulec działa inaczej niż w starym.

This comma is required in standard writing.

Yes, Polish word order is fairly flexible.

This sentence starts with W nowym samochodzie, which sets the scene first: in the new car. That is a very natural way to present the information.

You could also say something like:

• Fotel w nowym samochodzie jest wygodniejszy, ale hamulec działa inaczej niż w starym.

That is also grammatical, but it shifts the focus slightly toward fotel first.

So the original word order is natural and emphasizes the setting before talking about the seat.

Because there are actually two separate clauses, each with its own subject and verb:

1. fotel jest wygodniejszy
2. hamulec działa inaczej niż w starym

The conjunction ale joins these two clauses. Each verb agrees only with its own subject:

• fotel → jest
• hamulec → działa

So there is no reason for a plural verb here.

Yes. Samochód is a masculine singular noun, and that affects adjective agreement.

That is why you get:

• nowy samochód in the nominative
• w nowym samochodzie in the locative

The adjective must match the noun’s gender, number, and case, so once samochód changes case, the adjective changes too.

The same applies to the understood noun in w starym: the hidden noun is still samochodzie, so the adjective remains masculine singular locative.