Questions & Answers about Vauhti kasvoi nopeasti.
- vauhti is the subject: speed, pace, or momentum
- kasvoi is the verb: past tense of kasvaa = grew / increased
- nopeasti is an adverb: quickly / rapidly
So structurally it is:
subject + verb + adverb
Because it is the subject of the sentence, and subjects are typically in the nominative in Finnish.
The nominative singular form is the basic dictionary-like form of the noun, and here that form is vauhti.
Kasvoi is in the past tense (often called the imperfect in Finnish grammar).
It is the 3rd person singular form of kasvaa.
- kasvaa = to grow, to increase
- kasvoi = grew, increased
So the sentence describes something that happened in the past.