Learn Finnish: Kokeneempi ryhmä sieti painottomuutta paremmin kuin odotimme. - The more experienced group tolerated weightlessness better than we expected.

It is the comparative form of the past active participle kokenut (experienced), which comes from the verb kokea (to experience). To form the comparative, you take the inflectional stem of the participle, which is kokenee-, and add the comparative suffix -mpi.

Why is painottomuutta in the partitive case?

The verb sietää (to tolerate or withstand) is a partitive verb. The thing being tolerated must always take the partitive case, which is why the nominative painottomuus becomes painottomuutta.

How is the word painottomuus built from its root?

It is built from the noun paino (weight). Adding the suffix -ton makes the adjective painoton (weightless). The stem of this adjective is painottoma-, so when we add the suffix -uus, it creates the abstract noun painottomuus (weightlessness).

Why does the sentence use paremmin instead of parempi?

Parempi is an adjective meaning better, used to modify nouns (like parempi ryhmä). Paremmin is an adverb, which is the comparative form of hyvin (well). Here it modifies the verb sieti, telling us how the group tolerated the situation.

Why is the verb odotimme in the simple past instead of the past perfect (had expected)?