Горячий чай быстро остывает на столе.

Because чай is a masculine singular noun, and the adjective must agree with it in gender, number, and case.

Here, чай is:

• masculine
• singular
• nominative

So the adjective also has to be masculine singular nominative:

• горячий чай = hot tea

Compare:

• горячая вода = hot water, because вода is feminine
• горячее молоко = hot milk, because молоко is neuter

Because чай is the subject of the sentence — it is the thing doing the action, or more accurately, the thing undergoing the action.

In Горячий чай быстро остывает на столе, the tea is what cools down, so Russian uses the nominative:

• чай = tea, subject form

If tea were an object instead, it might appear in another case.

Остывает is the imperfective present form of остывать.

It is used here because the sentence describes:

• a general fact
• a repeated situation
• or a process in progress

So Горячий чай быстро остывает на столе means something like:

• hot tea cools down quickly on the table
• hot tea is cooling down quickly on the table

By contrast, остынет is the perfective future form from остыть:

• Чай остынет = the tea will cool down / will have cooled down

So:

• остывает = is cooling down / cools down
• остынет = will cool down

These are an aspect pair:

• остывать = imperfective
• остыть = perfective

Russian aspect is very important.

Imperfective: остывать

Used for:

• process
• repetition
• general facts
• ongoing action

Examples:

• Чай быстро остывает. = Tea cools down quickly.
• Суп остывал на столе. = The soup was cooling on the table.

Perfective: остыть

Used for:

• completion
• one whole event
• result

Examples:

• Чай остыл. = The tea cooled down / has gone cold.
• Суп остынет через десять минут. = The soup will cool down in ten minutes.

So in your sentence, остывает focuses on the process, not the completed result.

Остывать is usually intransitive. It means to cool down, not to cool something down.

So:

• Чай остывает. = The tea is cooling down.

But you would not normally say that someone остывает чай to mean cools the tea.

If you want to cool something, Russian usually uses another verb, such as:

• охлаждать / охладить
• sometimes остужать / остудить

For example:

• Я остудил чай. = I cooled the tea down.
• Чай остывает. = The tea is cooling down.

Yes. Быстро is the adverb form related to the adjective быстрый.

• быстрый = fast, quick
• быстро = quickly, fast

In this sentence, быстро modifies the verb остывает, so it tells us how the tea cools down:

• быстро остывает = cools down quickly

This is similar to English:

• quick → adjective
• quickly → adverb

Russian often forms adverbs from adjectives like this:

• медленный → медленно = slow → slowly
• тихий → тихо = quiet → quietly

Because на столе expresses location: the tea is on the table.

After на, Russian can use different cases depending on the meaning:

1. на + accusative = movement onto something

• на стол = onto the table

Example:

• Я поставил чай на стол. = I put the tea onto the table.

2. на + prepositional = location on something

• на столе = on the table

Example:

• Чай стоит на столе. = The tea is on the table.

In your sentence, the tea is already there, so Russian uses the prepositional case:

• на столе

It can do both.

Literally, на столе means:

• on the table

But in context, it often also implies:

• while sitting on the table
• when left on the table
• as it stands on the table

So the sentence can feel slightly broader than just pure location. It suggests the tea cools quickly when it is sitting there on the table.

That kind of small contextual extension is very normal in Russian.

Russian has no articles like English a/an/the.

So чай can mean:

• tea
• a tea
• the tea

The exact meaning depends on context.

In your sentence, English might translate it as:

• Hot tea cools down quickly on the table or
• The hot tea cools down quickly on the table

Russian leaves that unstated unless context makes it clear in some other way.

This is one of the biggest differences from English.

Yes. Russian word order is more flexible than English because case endings show grammatical roles.

The neutral order here is:

• Горячий чай быстро остывает на столе.

But other orders are possible, depending on emphasis:

• На столе горячий чай быстро остывает.
  Emphasis on on the table
• Быстро остывает горячий чай на столе.
  More literary or marked; emphasis on the action
• Горячий чай на столе быстро остывает.
  Slightly emphasizes the location before the verb

The basic meaning stays similar, but the focus changes.

For learners, the original order is a good neutral pattern: subject + adverb + verb + location

Because of the verb ending.

The verb остывать in the present tense is conjugated like this:

• я остываю = I cool down / am cooling down
• ты остываешь = you cool down
• он / она / оно остывает = he / she / it cools down
• мы остываем = we cool down
• вы остываете = you cool down
• они остывают = they cool down

So -ет in остывает shows third person singular.

Since чай is singular, the verb also appears in singular:

• чай остывает

If the subject were plural:

• Напитки остывают. = The drinks cool down.

No. They describe different temperatures.

• горячий = hot
• тёплый = warm

So:

• горячий чай = hot tea
• тёплый чай = warm tea

This matters with остывать, because something that is горячий can остывать and become тёплый, and later even холодный.

A rough temperature progression could be:

• горячий = hot
• тёплый = warm
• прохладный / холодный = cool / cold

The stress is:

• горЯчий
• чай
• бЫстро
• остывАет
• на столЕ

So the whole sentence is pronounced roughly like:

• горЯчий чай бЫстро остывАет на столЕ

Stress is very important in Russian because it is not always predictable and can affect vowel pronunciation.

For example, unstressed о is often pronounced more like a in actual speech, so остывает will not sound exactly like it looks if you pronounce every vowel fully.

Not usually, at least not with the same meaning.

• быстро = quickly, fast
• скоро = soon

So:

• быстро остывает = cools down quickly
• скоро остынет = will cool down soon

That means скоро works more naturally with a future or result idea:

• Горячий чай скоро остынет. = The hot tea will cool down soon.

But in your sentence, быстро is the natural choice because it describes the speed of the process.

It can be either, depending on context.

Without articles, Russian often leaves this open.

General statement

• Горячий чай быстро остывает на столе.
• Hot tea cools down quickly on the table.

This sounds like a general observation.

Specific situation

In the right context, it could also mean:

• The hot tea is cooling down quickly on the table.

For example, if you are looking at a particular cup, the same Russian sentence can describe that situation too.

So the sentence is somewhat flexible in interpretation. Context decides.