Learn Finnish: Urheilija harrastaa yleisurheilua ja juoksee kilometrin joka aamu. - The athlete does track and field and runs a kilometer every morning.

Even though running can be an ongoing process, Finnish treats expressions of exact distance, weight, and measure as total objects. In an affirmative sentence, reaching that exact amount takes the genitive accusative (ending in -n) to show the full distance was completed. If the sentence were negative, it would become partitive (ei juokse kilometriä).

Why does the first verb take a partitive object (yleisurheilua) but the second verb takes an accusative object (kilometrin)?

The verb harrastaa (to do as a hobby) inherently describes an open-ended, continuous activity, so it always demands a partitive object. In contrast, juoksee kilometrin expresses the completion of a specific, measurable goal, which triggers the total object rule for exact distances.

Why doesn't the time expression joka aamu have a case ending, like aamulla (in the morning) does?

The word joka (every/each) freezes the phrase in the nominative case. While you would use the adessive case to say 'in the morning' (aamulla), phrases starting with joka stay uninflected, such as joka aamu (every morning) or joka päivä (every day).

The word yleisurheilua looks like a compound. What does it literally mean?