El frasco de vidrio se cayó al suelo, pero no se rompió.

In Spanish, caerse is very commonly used for to fall down / to fall over, especially when talking about a person or object that accidentally falls.

• El frasco cayó = the jar fell
• El frasco se cayó = the jar fell down / the jar accidentally fell

Both can be possible, but se cayó sounds very natural here because it describes an event happening to the jar, not something deliberate.

This se is not really translated as itself in English. It is part of the verb caerse.

Not in the usual English sense of reflexive.

In se cayó, the se is part of the pronominal verb caerse. It does not mean the jar literally fell itself. Instead, it often gives the idea of:

• an event that happened
• loss of position
• often something accidental or sudden

So although it uses a reflexive-looking pronoun, you should learn caerse as a common verb meaning to fall down.

Because a + el contracts to al.

So:

• a + el = al
• de + el = del

That is why Spanish says:

• al suelo = to the ground / onto the floor

This contraction is required, except with the article in some proper names like a El Escorial.

Here, suelo means floor or ground, depending on context.

In this sentence, since a jar falls and does not break, al suelo is naturally understood as:

• onto the floor
• sometimes more generally to the ground

If the context is indoors, English would usually say the floor. If outdoors, the ground may fit better.

Spanish often expresses material with de + noun:

• de vidrio = made of glass
• de madera = made of wood
• de metal = made of metal

So el frasco de vidrio literally means the jar of glass, but in natural English we say the glass jar.

Spanish can sometimes use adjectives for materials, but de vidrio is the normal and natural way here.

These words can overlap, but they are not exactly the same.

• frasco: jar, bottle, small container, often for medicine, perfume, preserves, etc.
• botella: bottle
• tarro: jar, pot, or container, depending on region and context

In Spain, frasco often suggests a container, sometimes smaller or more compact than a botella. In this sentence, frasco works well for jar.

Because both refer to completed events in the past.

• se cayó = it fell
• no se rompió = it did not break

The preterite is used because the sentence describes specific finished events: the jar fell, and it did not break.

If you used the imperfect, it would sound like background description or repeated action, which is not the idea here.

Spanish usually omits subject pronouns when they are not needed.

The subject is already clear from the context:

• El frasco de vidrio se cayó...
• ...pero no se rompió

Once el frasco has been mentioned, Spanish does not need to repeat él. Adding él would usually be for emphasis or contrast.

This is very normal in Spanish and is one of the big differences from English.

Because romper and romperse are different in use.

• romper algo = to break something
  
  • Juan rompió el vaso = Juan broke the glass
• romperse = to break / to get broken
  
  • El vaso se rompió = the glass broke

In your sentence, the jar is the thing that would break, so Spanish uses se rompió.

This is a very common pattern in Spanish when something changes state on its own or without mentioning who caused it.

Yes, often a little.

The sentence suggests that falling to the floor would normally make a glass jar break, so pero no se rompió adds a contrast:

• it fell
• but surprisingly, it did not break

That contrast is carried by pero and by the real-world expectation that glass is fragile.

Yes, that is grammatically correct.

However, se cayó is often more natural in everyday Spanish when something accidentally falls over or drops. Using cayó can sound a bit more neutral or literary depending on context.

So:

• se cayó = very common in everyday speech
• cayó = also correct, but slightly different in feel

In Spain, both can refer to glass, but they are not always identical.

• vidrio often refers to the material in a general or technical sense
• cristal is also very common for everyday glass, especially things like windows, drinking glasses, or broken glass

In this sentence, de vidrio sounds completely natural for made of glass.
If you said de cristal, it might sometimes suggest a finer or more delicate kind of glass, depending on context.

A learner may notice the written accent marks.

• cayó is stressed on the last syllable: ca-YÓ
• rompió is stressed on the last syllable: rom-PIÓ

The accent marks show that stress.

Very roughly in Spain Spanish:

• se cayó ≈ seh kah-YOH
• se rompió ≈ seh rom-PYOH

Also note that ll in cayó is not present here because the verb is caer. The form is cayó, with y, not calló.

Spanish word order is fairly flexible, but this order is the most neutral and natural:

• subject: El frasco de vidrio
• verb: se cayó
• place/destination: al suelo

You could move al suelo for emphasis in some contexts, but the given order is the straightforward way to tell the event.

For example:

• El frasco de vidrio se cayó al suelo = neutral
• Al suelo se cayó el frasco de vidrio = more marked, more dramatic or literary