La bola cayó al suelo.

Because bola is a singular feminine noun, so it normally takes the feminine singular article la when you mean the ball.

• la = the for a feminine singular noun
• bola = a feminine noun

So:

• la bola = the ball
• una bola = a ball

In this sentence, la bola is the subject: it is the thing that fell.

It can be, but learners should know that pelota is also very common, and often more natural for a physical ball used in games.

Broadly speaking:

• pelota = ball, especially a sports ball or toy ball
• bola = ball, sphere, lump, or something round

So La bola cayó al suelo is grammatically fine, but depending on context, many speakers might also say:

• La pelota cayó al suelo.

In Spain, both words exist, but pelota is often the more everyday word for an actual ball.

Cayó is the 3rd person singular preterite form of the verb caer (to fall).

That form is used because:

• the subject is singular: la bola
• the action happened in the past
• it is seen as a completed event

So:

• caer = to fall
• cayó = it fell / she fell / he fell depending on context

In this sentence, it means the ball fell.

A few useful related forms:

• cae = it falls / is falling
• caía = it was falling / used to fall
• cayó = it fell

The accent mark shows both pronunciation and which verb form it is.

• cayó is pronounced with stress on the last syllable: ca-YÓ
• without the accent, cayo would be a different word or would be read differently

This accent helps distinguish the past tense form clearly.

For learners, the important thing is simply:

• cayó = past tense, he/she/it fell

Because in Spanish, a + el contracts to al.

So:

• a el suelo → al suelo

This contraction is required in normal Spanish.

Examples:

• Voy al parque.
• Llegó al final.
• Cayó al suelo.

The only common exception is when el is part of a proper name, such as:

• a El Escorial

But here suelo is just a normal noun, so it must be al suelo.

Here, suelo means the ground or the floor surface.

It is a very natural choice in this kind of sentence.

Some comparisons:

• suelo = ground/floor surface in a general sense
• tierra = earth, soil, ground outdoors
• piso = in Spain, mainly flat/apartment; in some Latin American varieties it can also mean floor

So in Spain, suelo is especially natural for floor/ground surface.
That is why cayó al suelo sounds very normal.

Compare:

• La pelota cayó al suelo. = The ball fell to the ground/floor.
• La pelota está en el suelo. = The ball is on the ground/floor.

Because al suelo expresses movement toward the ground, while en el suelo expresses location on the ground.

So:

• cayó al suelo = fell to the ground
• está en el suelo = is on the ground

This is a very common distinction in Spanish:

• a often shows direction or destination
• en often shows location

So after a verb like caer, al suelo is the natural choice when you focus on the fall itself.

Because Spanish often omits subject pronouns when the subject is already clear.

In English, you need it fell.
In Spanish, the verb form often tells you enough, and the noun is already present:

• La bola cayó al suelo.

You could technically say:

• Ella cayó al suelo.

But that would mean she fell to the ground, not it, because Spanish pronouns reflect grammatical gender and are usually not used for things the way English uses it.

So Spanish normally just uses the noun itself, or leaves the pronoun out if the context is clear.

Yes, you could, and it is very common in everyday Spanish.

Both are possible:

• La bola cayó al suelo
• La bola se cayó al suelo

In many contexts, caerse sounds a bit more natural in everyday speech for an accidental fall or something falling down.

Very roughly:

• caer = to fall
• caerse = to fall down / to end up falling, often with an accidental feel

That said, cayó al suelo is completely correct and natural.

Yes, but La bola cayó al suelo is the most straightforward and neutral order.

Spanish word order is more flexible than English. You might also hear:

• Cayó la bola al suelo.

But this sounds more marked or literary, and it is less likely to be the first version taught to a learner.

The standard beginner-friendly structure is:

• subject + verb + complement
• La bola + cayó + al suelo

A simple pronunciation guide is:

la BO-la ka-YÓ al SWE-lo

A few notes:

• ll in cayó is not involved here; the y in cayó sounds like a Spanish y
• the stress in cayó is on the last syllable: -yó
• suelo is stressed on sue-

In standard Spain Spanish, a rough approximation is:

la BO-la ka-YO al SWEH-lo

The exact sound of c in cayó is like an English k, because it comes before a.