Questions & Answers about Время пролетает незаметно, но не впустую.
Why is the prefix про- used in пролетает here instead of just saying Время летит?
Both время летит (time flies) and время пролетает (time flies by) are common metaphorical uses of verbs of motion. The prefix про- adds the idea of passing through or going past. Here, it emphasizes that a period of time is slipping past us from beginning to end, rather than just describing the speed of time in general.
Why use the imperfective verb пролетает rather than the perfective пролетит?
The imperfective пролетает expresses a general, ongoing truth about how time behaves. If you wanted to say that a specific event in the future 'will fly by', you would switch to the perfective form: неделя пролетит незаметно (the week will fly by unnoticeably).
How does впустую compare to other words for 'in vain' like зря or напрасно?
Впустую literally comes from the preposition в (into) plus the adjective пустой (empty). It creates a vivid image of effort or time pouring into an empty void. While зря and напрасно are very common synonyms for 'in vain', впустую strongly emphasizes a total lack of productive results, which perfectly contrasts with the time flying.
What is the root of the adverb незаметно?