Сегодня у нас лабораторная по физике, и нужно прийти пораньше.

In Russian, у + genitive is a very common way to express that someone has something, or that something exists for / with someone.

• у нас literally means at us or with us
• In context, Сегодня у нас лабораторная means Today we have a lab

This is much more natural in Russian than trying to translate English have directly.

Examples:

• У меня урок. = I have a lesson.
• У нас экзамен. = We have an exam.

So here, у нас does not mean physical location as much as for us / on our schedule.

Yes, historically it is an adjective, but in modern Russian it is very commonly used as a noun by itself.

It is short for:

• лабораторная работа = lab work / laboratory exercise

In everyday speech, Russians often drop работа and simply say:

• лабораторная = lab session / lab assignment

This is very common in school and university contexts.

So:

• Сегодня у нас лабораторная = literally something like Today we have a lab (exercise/session)

Физике is in the dative case because the preposition по often requires the dative.

In this kind of academic context, по + dative means in / on the subject of.

So:

• по физике = in physics / for physics / on physics
• экзамен по математике = math exam
• книга по истории = a book on history
• урок по английскому = English lesson

So лабораторная по физике means a physics lab.

Yes, Russian word order is flexible.

Сегодня is placed first because it sets the time frame right away: Today...

You could also hear:

• У нас сегодня лабораторная по физике...
• Лабораторная по физике у нас сегодня...
  though this is less neutral and more marked

Putting Сегодня first is very natural because it highlights today as the starting point of the message.

Because и is joining two clauses here, not just two single words.

The two parts are:

1. Сегодня у нас лабораторная по физике
2. нужно прийти пораньше

These are two separate predicative units, so Russian normally uses a comma before и in this situation.

Compare:

• У нас лабораторная и семинар.
  No comma: just two nouns
• У нас лабораторная, и нужно прийти пораньше.
  Comma: two clauses

Russian often uses impersonal constructions where English would use something like we need to... or you have to...

• нужно прийти = it is necessary to arrive / one needs to arrive

This sounds natural and slightly less direct than мы должны прийти.

Compare:

• Нужно прийти пораньше. = We need to come early / It’s necessary to arrive early.
• Мы должны прийти пораньше. = We must arrive early.

The version with нужно is very common in everyday Russian and often leaves the subject understood from context.

The subject is understood from context.

The first clause says:

• у нас лабораторная = we have a lab

So in the second clause, it is natural to understand:

• (нам) нужно прийти пораньше = (we) need to come earlier

Russian often omits words that are obvious from context. If you wanted to make it explicit, you could say:

• Сегодня у нас лабораторная по физике, и нам нужно прийти пораньше.

That is also correct, just slightly fuller.

Because прийти is perfective, and here the speaker is talking about a single completed arrival.

• прийти = to arrive / to come once, as a completed action
• приходить = to come / be coming, repeated or ongoing, or more general

In this sentence, the idea is:

• We need to arrive early for today’s lab

That is a one-time event, so прийти is the natural choice.

Examples:

• Нужно прийти к девяти. = You need to arrive by nine.
• Он часто приходит рано. = He often comes early.

Not exactly. Пораньше means earlier or a bit earlier than usual / than expected.

It comes from:

• рано = early
• раньше = earlier
• пораньше = a little earlier / somewhat earlier

So:

• нужно прийти пораньше = we need to come a bit earlier

This often suggests:

• earlier than normal
• earlier than the official start
• early enough for preparation

It is slightly softer and more conversational than simply saying раньше.

No.

• лаборатория = laboratory as a room or lab facility
• лабораторная (работа) = lab class / lab assignment / laboratory exercise

So in this sentence, лабораторная does not mean the room. It means the class activity or assignment.

Compare:

• Мы в лаборатории. = We are in the laboratory.
• У нас лабораторная по физике. = We have a physics lab.

Yes, that is a helpful rough breakdown, and it shows how Russian is structured. A literal gloss would be something like:

• Сегодня = today
• у нас = at us / for us
• лабораторная = lab session
• по физике = in physics
• и = and
• нужно = it is necessary
• прийти = to arrive
• пораньше = a bit earlier

But in natural English, you would say:

• Today we have a physics lab, and we need to come a bit early.

Literal translation is useful for understanding grammar, but not for producing natural English.

Yes, but the nuance changes a little.

• раньше = earlier
• пораньше = a bit earlier / somewhat earlier

So:

• нужно прийти раньше sounds more direct and plain: need to arrive earlier
• нужно прийти пораньше sounds a little softer and more idiomatic in conversation

In many situations, пораньше is what a native speaker would naturally choose.

The main stress pattern is:

• Сего́дня у нас лаборато́рная по фи́зике, и ну́жно прийти́ пора́ньше.

A few important ones:

• сего́дня
• лаборато́рная
• фи́зике
• ну́жно
• прийти́
• пора́ньше

Stress matters in Russian, so it is worth learning these together with the words.