La gravedad parece más fácil cuando la ecuación está bien explicada.

In Spanish, abstract nouns are often used with the definite article much more than in English. So la gravedad is very natural, even though English often just says gravity without the.

This is common with school subjects, ideas, and general concepts:

• La historia es interesante = History is interesting
• La música me ayuda a estudiar = Music helps me study
• La gravedad parece más fácil... = Gravity seems easier...

So the article is not unusual here; it is simply standard Spanish usage.

Because the subject is la gravedad, which is singular.

• la gravedad = singular
• therefore the verb must also be singular: parece

If the subject were plural, then you would use parecen:

• Las matemáticas parecen más fáciles = Maths seem easier

Even though the sentence also contains la ecuación, that noun belongs to the cuando clause and is not the subject of parece.

In Spanish, más + adjective can sometimes express a general idea of more/easier than before, easier in that situation, or easier than it seems otherwise, even when the second part of the comparison is not stated explicitly.

So parece más fácil means something like:

• seems easier
• seems easier that way
• seems easier than usual / than before / than in other circumstances

This is very normal in both Spanish and English. We often leave the second half of the comparison understood from context.

Because fácil is an adjective that has the same form for masculine and feminine.

So you get:

• un problema fácil
• una cuestión fácil

The adjective does change for number, though:

• un problema fácil
• dos problemas fáciles

So in your sentence, más fácil is correct because it agrees in meaning with la gravedad, but fácil itself does not need a separate feminine form.

Cuando means when, and here it introduces a situation that is presented as a general or real circumstance:

• La gravedad parece más fácil cuando...
  = Gravity seems easier when...

If you used si, the meaning would shift toward if:

• ...si la ecuación está bien explicada
  = ...if the equation is well explained

That is not wrong in every context, but it is a slightly different idea. Cuando sounds more like a general truth or repeated experience: whenever the equation is well explained, gravity seems easier.

Spanish often uses estar + past participle to describe a state or condition resulting from an action.

So la ecuación está bien explicada means the equation is in a well-explained state, or simply the equation is well explained.

This is more natural here than es bien explicada. In many cases:

• estar + participle = focuses on the resulting condition
• ser + participle = more like a passive construction focused on the action itself

Compare:

• La puerta está cerrada = The door is closed
• La puerta fue cerrada por Ana = The door was closed by Ana

In your sentence, the focus is the condition of the equation, so está bien explicada is the natural choice.

Because explicada agrees with la ecuación, which is:

• feminine
• singular

So the participle must match it:

• el problema está bien explicado
• la ecuación está bien explicada
• los problemas están bien explicados
• las ecuaciones están bien explicadas

This agreement is very common with estar + participle.

Bien is an adverb, and it modifies explicada in the sense of well explained.

So:

• explicada = explained
• bien explicada = well explained

This works just like:

• bien escrito = well written
• bien organizado = well organised
• bien preparado = well prepared

Notice that bien does not change form. It is an adverb, not an adjective.

Grammatically, you could form a sentence with es, but the meaning would change.

• parece más fácil = seems easier
• es más fácil = is easier

Parece expresses an impression or appearance. It is softer and more subjective. That fits well here, because the idea is about how gravity feels to the learner when the equation is explained clearly.

Using es would sound more definite and factual.

No. The main subject of the sentence is la gravedad.

The sentence is structured like this:

• La gravedad = subject of the main clause
• parece más fácil = main verb phrase
• cuando la ecuación está bien explicada = subordinate clause introduced by cuando

Inside that subordinate clause:

• la ecuación = subject
• está bien explicada = verb phrase

So there are two clauses, each with its own subject.

This word order is very normal in Spanish:

• cuando
  • subject + verb phrase

So:

• cuando la ecuación está bien explicada

Spanish often keeps a straightforward subject-verb order in subordinate clauses, especially when the subject is explicitly stated.

You could sometimes rearrange parts for emphasis, but the version in the sentence is the most neutral and natural.

The accent mark changes the function:

• cuando = when as a conjunction or relative word
• cuándo = when? in direct or indirect questions

In your sentence, it is cuando without an accent because it introduces a clause:

• La gravedad parece más fácil cuando...

Examples with cuándo:

• ¿Cuándo empieza la clase? = When does class start?
• No sé cuándo empieza la clase = I don’t know when class starts

So the version in your sentence is correct because it is not a question.

Yes, it is natural and understandable Spanish. A native speaker could say it exactly like that.

Depending on context, they might also say things like:

• La gravedad parece más fácil de entender cuando la ecuación está bien explicada.
• La gravedad resulta más fácil cuando la ecuación está bien explicada.

But your original sentence is perfectly fine. It sounds like a general statement about learning or understanding a topic.