Learn Hardcore Indonesian: Guru fisika kami menjelaskan teori dengan jelas di perpustakaan. - Our physics teacher explains the theory clearly in the library.

guru – teacher
fisika – physics
guru fisika – physics teacher
kami – we / us (exclusive: not including the person spoken to)
guru fisika kami – our physics teacher
menjelaskan – to explain
- jelas – clear
- meN‑ … ‑kan – a common verb pattern; here it makes jelas (clear) into menjelaskan (to make something clear, to explain)
teori – theory
dengan – with, by (used to form adverbs)
jelas – clear
dengan jelas – clearly
di – at / in
perpustakaan – library
di perpustakaan – in the library / at the library

So the structure is:
[Guru fisika kami] [menjelaskan] [teori] [dengan jelas] [di perpustakaan].
[Our physics teacher] [explained] [the theory] [clearly] [in the library].

Why does kami (our) come at the end of guru fisika kami, not before like in English?

In Indonesian, possessors usually come after the thing possessed.

guru kami – our teacher
buku saya – my book
rumah mereka – their house

So:

guru fisika kami literally: teacher physics our
→ natural English: our physics teacher

Word order pattern:
[noun] [modifier(s)] [possessor]

Here:

guru (noun: teacher)
fisika (modifier: physics)
kami (possessor: our)

Putting kami before (kami guru fisika) is ungrammatical.

What exactly is guru fisika? Is fisika an adjective here, or a noun?

Fisika is still a noun (“physics”), but Indonesian often uses noun + noun to mean “X of Y” or “Y X”:

guru matematika – math teacher (teacher of mathematics)
guru bahasa Inggris – English teacher (teacher of English)
buku sejarah – history book (book about history)

So guru fisika is a noun–noun compound that means physics teacher (a teacher whose subject is physics). There is no special adjective form like “physical” here; you just stick the subject noun after guru.

What is the difference between kami and kita? Could I say Guru fisika kita instead?

Both mean we / our, but:

kami = we / our, excluding the person you’re talking to
kita = we / our, including the person you’re talking to

So:

guru fisika kami – our physics teacher (the speaker’s group, not including the listener)
guru fisika kita – our physics teacher (including the listener in “our”)

You can say Guru fisika kita menjelaskan teori… if you want to include the listener as part of the group that shares that teacher.

Does guru fisika kami mean one teacher or several teachers?

By itself, guru fisika kami is number-neutral. It could mean:

our physics teacher (singular), or
our physics teachers (plural), depending on context.

To make it clearly plural, you can say:

guru-guru fisika kami – our physics teachers
para guru fisika kami – our physics teachers (more formal/literary)

Similarly, teori could be “theory” or “theories” unless you specify:

teori-teori – theories (explicit plural)

How do we know if this sentence is in the past (explained) or present (explains)? There’s no tense marker.

Indonesian verbs generally do not change form for tense. Menjelaskan can mean:

explains
is explaining
explained
will explain

The tense is understood from context or from time words:

Kemarin guru fisika kami menjelaskan teori…
Yesterday our physics teacher explained the theory…
Sekarang guru fisika kami menjelaskan teori…
Now our physics teacher is explaining the theory…
Besok guru fisika kami akan menjelaskan teori…
Tomorrow our physics teacher will explain the theory…

Without context, Guru fisika kami menjelaskan teori… is ambiguous about time, but that’s normal and natural in Indonesian.

What is the relationship between jelas and menjelaskan?

jelas – clear (adjective)
- Penjelasannya sangat jelas. – The explanation is very clear.
menjelaskan – to explain, to make something clear (verb)
- Guru fisika kami menjelaskan teori. – Our physics teacher explains the theory.

Formally, menjelaskan is built from:

jelas (clear)
meN‑ … ‑kan (a verbal affix pair that often makes a causative verb: “to make X [adj] / to do X to something”)

So menjelaskan [teori] is “to make [the theory] clear” → “to explain [the theory]”.

Why is it dengan jelas “clearly” instead of just jelas?

Indonesian often uses dengan + adjective to form an adverb, similar to English with X / in an X way:

dengan jelas – clearly
dengan cepat – quickly
dengan hati-hati – carefully

So:

Guru fisika kami menjelaskan teori dengan jelas.
Our physics teacher explained the theory clearly.

You can sometimes use jelas alone as an adverb, especially in informal speech:

Dia menjelaskan teori itu jelas sekali.
He explained that theory very clearly.

But dengan jelas is the textbook, neutral adverbial form.

Can dengan jelas be put in a different place in the sentence?

Yes, adverbial phrases in Indonesian are fairly flexible, as long as the sentence remains clear. Some possibilities:

Guru fisika kami menjelaskan teori dengan jelas di perpustakaan.
Guru fisika kami menjelaskan teori di perpustakaan dengan jelas.
Dengan jelas, guru fisika kami menjelaskan teori di perpustakaan. (more formal/written style)

What you usually don’t do is split the verb and its object unnaturally, like:

✗ Guru fisika kami menjelaskan dengan jelas teori di perpustakaan.
(not wrong grammatically, but sounds awkward because teori is separated from menjelaskan by the adverb)

A safe rule:
Verb + object, then adverbs (manner, place, time) after that, unless you front an adverb for emphasis.

Does teori here mean “the theory” or “a theory”? There are no articles.

Indonesian has no articles like a / an / the, so teori by itself can be:

the theory
a theory
theories (in a generic sense, depending on context)

To make it more specific:

sebuah teori – a theory (one theory, fairly neutral)
teori itu – that theory / the theory (already known or being pointed out)
teori-teori itu – those theories (specific, plural)

In your sentence, teori is just “the theory” or “the theory (they were studying)”, from context.

Why do we need di before perpustakaan? Can we say just perpustakaan?

Di is a preposition meaning in / at / on (for location). To express location, you normally need di:

di rumah – at home
di sekolah – at school
di perpustakaan – at / in the library

Saying just perpustakaan at the end:

✗ … jelas perpustakaan.

is ungrammatical as a place phrase; you need di to mark it as a location.

Related contrasts:

di perpustakaan – in/at the library (location)
ke perpustakaan – to the library (movement toward)
dari perpustakaan – from the library (movement away)

You might also see di dalam perpustakaan – inside the library (emphasizing inside).

Could we move di perpustakaan to the front of the sentence?

Yes. Putting the place expression first is common, especially in narrative or when you want to set the scene:

Di perpustakaan, guru fisika kami menjelaskan teori dengan jelas.
In the library, our physics teacher clearly explained the theory.

This sounds natural. The main clause is unchanged; you just prepose the location for emphasis/context.

Could we drop kami and just say Guru fisika menjelaskan teori…?

You can, but the meaning changes slightly:

Guru fisika menjelaskan teori…
A / the physics teacher explained the theory… (generic or unspecified belonging)
Guru fisika kami menjelaskan teori…
Our physics teacher explained the theory… (specifically our teacher)

So yes, kami is optional grammatically, but it adds the nuance of possession: it’s the teacher that belongs to “us” (our class, our school group, etc.).

How would I say “Our physics teacher explained the theory to us clearly in the library”? Where does “to us” go?

You need an indirect object phrase, usually with kepada or pada:

Guru fisika kami menjelaskan teori kepada kami dengan jelas di perpustakaan.

Breakdown:

kepada kami – to us
You already have kami as the possessor (guru fisika kami), and a second kami as the indirect object (kepada kami).

This is not redundant in Indonesian; it’s natural:

Guru fisika kami – our physics teacher (who belongs to us as students)
menjelaskan teori kepada kami – explained the theory to us

Why is the word order Subject – Verb – Object – Adverbs? Is that the normal pattern in Indonesian?

Yes, the most common basic word order is S – V – O, then adverbials:

[Guru fisika kami] [menjelaskan] [teori] [dengan jelas] [di perpustakaan].
[Subject] [Verb] [Object] [Manner] [Place]

Similar patterns:

Saya makan nasi di rumah.
I eat rice at home.
Mereka menonton film bersama tadi malam.
They watched a movie together last night.

Adverbs of manner, place, time commonly come after the object, but can move for emphasis (especially time and place).

Is there a more casual or spoken alternative to menjelaskan?

Yes, in everyday informal Indonesian (especially in Jakarta/some urban speech), people often use colloquial forms derived from terang (clear/bright) or shortened forms:

nerangin (colloquial from menerangkan) – to explain
- Guru fisika kami nerangin teori itu di perpustakaan.
jelasin (shortened from menjelaskan) – to explain
- Guru fisika kami jelasin teori itu di perpustakaan.

These are informal. For writing, exams, or formal contexts, stick to menjelaskan.

If I wanted to say “the explanation was clear” instead of “explained clearly”, how would I change the sentence?

You would switch from using the verb “explain” to using the noun “explanation” plus jelas as an adjective:

Penjelasan guru fisika kami sangat jelas di perpustakaan.
Our physics teacher’s explanation was very clear in the library.

Or, keeping the library phrase more naturally with the verb:

Di perpustakaan, penjelasan guru fisika kami sangat jelas.
In the library, our physics teacher’s explanation was very clear.

Here:

penjelasan – explanation (noun, from jelas)
jelas – clear (adjective)
sangat – very (optional, just adds “very”)