Этот стул шатается, потому что один винт выпал.

Because стул is a masculine singular noun.

The demonstrative этот must agree with the noun in gender, number, and case:

• этот = masculine singular
• эта = feminine singular
• это = neuter singular
• эти = plural

So:

• этот стул = this chair
• эта лампа = this lamp
• это окно = this window

Here, стул is masculine, so этот is the correct form.

Because стул is the subject of the sentence, so it is in the nominative case.

In Этот стул шатается, the chair is the thing doing the action of wobbling, so Russian uses the nominative:

• стул = chair, nominative singular

If the noun had another role, its form might change. For example:

• Я вижу стул = I see a chair
  Here стул is in the accusative, but for an inanimate masculine noun, the form happens to look the same as the nominative.

Шатается means something like:

• is wobbling
• is unsteady
• is loose and rocking

For a chair, шатается suggests it is not firm or stable.

It comes from the verb шататься, which is an imperfective verb. In this sentence, it is 3rd person singular present tense:

• я шатаюсь
• ты шатаешься
• он / она шатается

So Этот стул шатается literally means This chair is wobbling / is unsteady.

The -ся ending is very common in Russian and often makes a verb reflexive or intransitive.

Here, шататься is the normal verb used for something that wobbles by itself or is loose/unsteady.

Compare:

• шатать = to shake something
• шататься = to shake / wobble / sway

So:

• Я шатаю стол = I am shaking the table
• Стол шатается = The table is wobbling

In this sentence, the chair is not actively shaking something else. It is itself unstable, so шатается is the natural form.

Because потому что introduces a subordinate clause.

The sentence has two parts:

• Этот стул шатается
• потому что один винт выпал

In Russian, when one clause explains the reason for another, a comma is normally used before потому что:

• Он ушёл, потому что устал.
• Я дома, потому что идёт дождь.

So the comma here is standard punctuation.

Yes, потому что is a very common way to say because.

It introduces the reason:

• Этот стул шатается, потому что один винт выпал. = This chair is wobbling because one screw fell out.

There are other ways to express because, such as:

• так как
• из-за того что

But потому что is one of the most common and straightforward choices in everyday Russian.

Because один винт is the subject of the second clause:

• один винт выпал = one screw fell out

Since винт is the thing that did the action of falling out, it stays in the nominative case.

Also, один must agree with винт:

• один = masculine singular nominative
• винт = masculine singular nominative

So the phrase is grammatically matched.

It can feel like both.

Literally, один means one, but in sentences like this it often has the natural sense of:

• one of the screws
• a screw

So один винт выпал can be understood as:

• one screw fell out
• a screw has fallen out

Russian has no articles like a or the, so words like один sometimes help give that kind of meaning in context.

Here винт means screw.

In other contexts, винт can also mean things like:

• a screw as a mechanical fastener
• a propeller
• a threaded part

But with a chair, the obvious meaning is screw.

So один винт выпал means that one of the screws has come out.

Выпал is the past tense masculine singular form of выпасть.

It means:

• fell out
• came out

Why this form?

1. Past tense: the event already happened.
2. Masculine singular: because the subject is винт, which is masculine singular.
3. Perfective aspect: выпасть focuses on the completed result — the screw has come out.

Compare:

• выпадать = imperfective, repeated or ongoing
• выпасть = perfective, completed event

So винт выпал means the screw did come out, as a finished event.

Russian past tense agrees with the subject in gender and number.

The subject is винт, which is masculine singular, so:

• выпал = masculine singular
• выпала = feminine singular
• выпало = neuter singular
• выпали = plural

Examples:

• Лампа упала. = The lamp fell.
  (лампа is feminine)
• Окно открылось. = The window opened.
  (окно is neuter)
• Винты выпали. = The screws fell out.
  (винты is plural)

So выпал matches винт.

Because Russian often leaves that out when it is obvious from context.

In this sentence, if a chair is wobbling because a screw is missing, it is easy to understand that the screw fell out of the chair or out of its fitting.

So один винт выпал sounds natural without adding more detail.

If you wanted to be more explicit, you could say something like:

• Один винт выпал из стула. = One screw fell out of the chair.

But in everyday speech, the shorter version is often enough.

Yes, Russian word order is fairly flexible, though some versions sound more natural than others.

The original sentence:

• Этот стул шатается, потому что один винт выпал.

is the most neutral and natural order.

You could also hear:

• Потому что один винт выпал, этот стул шатается.

This puts more emphasis on the reason first, but it can sound a bit more marked or explanatory.

Within the second clause, changing word order can also shift emphasis:

• Один винт выпал = neutral
• Выпал один винт = slightly more focus on the fact that a screw fell out

So yes, word order can move, but the original sentence is the best standard version for most situations.

A natural stress pattern would be something like:

• Э́тот стул шата́ется, потому́ что оди́н винт вы́пал.

Approximate stress points:

• Э́тот
• шата́ется
• потому́
• оди́н
• вы́пал

A learner should especially notice:

• шата́ется
• вы́пал

Russian stress is important because it is not always predictable from spelling.

Sometimes, yes, but the meaning may change slightly.

For example:

• качается = is swinging / rocking
• болтается = is dangling / wobbling loosely
• шатается = is unstable, loose, wobbling

For furniture, шатается is especially natural when a chair or table is loose because of bad assembly or a missing part.

So while other verbs may be possible in some contexts, шатается is a very good choice here.