Learn Hardcore Portuguese (Portugal): Quando a música tem um ritmo rápido, a Maria dança com ainda mais energia. - When the music has a fast rhythm, Maria dances with even more energy.

a música here literally means the music, referring to the music that is playing in that situation.
In Portuguese you often use the article even when English would talk about something more generally:
- A música é importante. = Music is important.
- Gosto da música. = I like (the) music.

So Quando a música tem um ritmo rápido is naturally When the music has a fast rhythm, not just “when music has a fast rhythm.”

Why is there an a before Maria? Do you always put an article before names?

In European Portuguese it is very common (though not absolutely obligatory) to use the definite article before personal names:

a Maria
o João
a Ana
o Pedro

So a Maria dança… is like saying Maria dances…, but sounding natural and colloquial in Portugal.

Notes:

In European Portuguese, using the article with names is standard in speech and informal writing.
In Brazilian Portuguese, people usually do not use the article before first names: they would more often say Maria dança…, without a.
You can drop the article in some more formal styles, headlines, etc., but a Maria is perfectly normal and very common in Portugal.

Does quando here mean “when” or “if”? Could I use se instead?

Quando literally means when, but in a sentence like this it introduces a general condition that is always (or usually) true. English can translate it as when(ever) or even as if:

Quando a música tem um ritmo rápido, a Maria dança…
- When the music has a fast rhythm, Maria dances with even more energy.
- Whenever the music has a fast rhythm, Maria dances…
- If the music has a fast rhythm, Maria dances…

Using se instead would sound more hypothetical or uncertain:

Se a música tiver um ritmo rápido, a Maria dança…
- If the music has a fast rhythm, Maria will dance…

So:

quando = each time that / whenever, for regular situations
se = if, for conditions that may or may not happen

Why do you say tem um ritmo rápido instead of just é rápida?

Both are grammatically possible, but they feel slightly different:

Quando a música tem um ritmo rápido…
- Literally: When the music has a fast rhythm…
- Focuses on the rhythm as a noun, something the music has.
Quando a música é rápida…
- Literally: When the music is fast…
- Describes the music itself as fast, in a more general way.

Portuguese often likes to express qualities as something that a thing has, using ter + noun:

Tem um som muito forte. = It has a very strong sound.
O filme tem uma história interessante. = The film has an interesting story.

So ter um ritmo rápido is a very natural way to talk specifically about the tempo or beat of the music. É rápida is correct, just a bit less specific about rhythm.

Why is it ritmo rápido and not ritmo rápida? Isn’t música feminine?

Adjectives agree with the noun they describe, not with the nearest word in the sentence.

ritmo is masculine (o ritmo)
rápido is describing ritmo, so it must be masculine: ritmo rápido

Even though música is feminine (a música), rápido is not describing música directly. It is describing the ritmo of the music.

Another example:

um carro vermelho = a red car (carro is masculine, so vermelho)
uma casa vermelha = a red house (casa is feminine, so vermelha)

Here we have:

um ritmo rápido = a fast rhythm (masc. noun + masc. adjective)

What does ainda add in com ainda mais energia? Could I just say com mais energia?

Yes, you can say com mais energia:

…a Maria dança com mais energia. = Maria dances with more energy.

The word ainda here adds the idea of even:

com ainda mais energia = with even more energy

So:

mais energia = more energy
ainda mais energia = even more energy (a stronger comparison)

In this sentence, ainda intensifies the increase in energy compared to normal.

Is the position of ainda fixed? Could I say com mais energia ainda or ainda com mais energia?

All three are possible, but they have slightly different feel:

com ainda mais energia (most common and neutral)
- Very natural, smooth, and clear.
com mais energia ainda
- Also correct.
- Puts a little extra emphasis at the end, on how much more energy there is.
ainda com mais energia
- Grammatically possible.
- Sounds a bit more marked or stylistic; you might hear it in speech with strong emphasis, or in more expressive writing.

In everyday language, com ainda mais energia is the most typical and recommended order.

Why is dança in the simple present? In English we often say “is dancing”.

Portuguese uses the simple present much more than English does, especially for:

regular/habitual actions
general truths

Here, a Maria dança… is describing what she typically does whenever the music has a fast rhythm. That’s why the simple present is the natural choice.

Compare:

Quando a música tem um ritmo rápido, a Maria dança com ainda mais energia.
- When the music has a fast rhythm, Maria dances with even more energy. (habit)
Agora, a Maria está a dançar com muita energia.
- Right now, Maria is dancing with a lot of energy. (action in progress)

In European Portuguese, the progressive is usually estar a + infinitive:

está a dançar (EP) ≈ está dançando (BP)

Why is there a comma after rápido?

In Portuguese, when a sentence starts with a subordinate clause introduced by words like quando, se, porque, etc., it is standard to put a comma before the main clause:

Quando a música tem um ritmo rápido, a Maria dança…
Se chover, não saímos de casa.
Quando eu chego a casa, janto.

If you invert the order (main clause first), the comma is usually not needed:

A Maria dança com ainda mais energia quando a música tem um ritmo rápido.

Could I say Quando a música tiver um ritmo rápido instead of tem?

Yes, but the meaning changes slightly.

Quando a música tem um ritmo rápido…
- General rule / habitual situation.
- Whenever the music has a fast rhythm, this is what happens.
Quando a música tiver um ritmo rápido…
- Future-oriented; talking about a specific future situation.
- When the music has a fast rhythm (in the future), then Maria will dance…

You’ll often see quando + future subjunctive (quando tiver) when referring to a specific future event:

Quando chegares, liga-me.
Quando tiveres tempo, diz-me.

In your sentence, we are describing a regular behaviour, so tem (present) is more natural.

Why is it com in dança com ainda mais energia? Could I use some other preposition?

Here com literally means with, expressing the manner or quality of the action:

dançar com energia = to dance with energy
falar com entusiasmo = to speak with enthusiasm

Other options exist but change the style or structure:

dança ainda mais energicamente
(adverb energicamente = more formal / written style)
dança cheia de energia
(literally “full of energy”, more descriptive, slightly different meaning)

So com (ainda) mais energia is the most straightforward, natural way to say with (even) more energy.

How do you pronounce ritmo and música?

Approximate European Portuguese pronunciation:

música: [MOO-zee-kɐ]
- mú-: like moo (but shorter)
- -si-: like zee
- -ca: like kɐ (a very reduced, almost dull uh sound)
ritmo: [REE-tmu]
- r- at the beginning: a throaty sound (like French or German r)
- -i-: like ee
- -tmo: t
  - m very close together; the o is very weak, almost like an unstressed u

The h in ritmo is silent; it only affects spelling, not pronunciation.