Learn Hardcore Indonesian: Ilmuwan menunjukkan lagi reaksi kecil di tabung kaca sambil memakai kacamata pelindung. - The scientist shows a small reaction again in a glass tube while wearing protective goggles.

It does not change form for singular or plural.
- Ilmuwan = a scientist / scientists (depending on context)
To make it clearly plural, you can say:
- para ilmuwan = scientists (a group of scientists)
- banyak ilmuwan = many scientists

There is no gender marking either, so ilmuwan can be male or female.

What is the difference between menunjuk and menunjukkan, and why is menunjukkan used here?

Both come from the root tunjuk:

menunjuk = to point (with a finger, etc.)
- Dia menunjuk ke papan tulis. = He/She pointed at the board.
menunjukkan = to show / to demonstrate (to make something visible or clear to someone)
- Dia menunjukkan hasil percobaan. = He/She showed the experiment results.

In the sentence:

Ilmuwan menunjukkan lagi reaksi kecil di tabung kaca...

the scientist is demonstrating a reaction (not just pointing at it), so menunjukkan is the natural choice.

What exactly does lagi mean here, and can it go in other positions?

Here, lagi means “again” (repetition):

menunjukkan lagi = shows it again

Common meanings of lagi:

again
- Coba lagi. = Try again.
more / another
- Mau satu lagi? = Do you want one more?
currently / in the middle of (colloquial, like “be -ing”)
- Dia lagi makan. = He/She is eating (right now).

Position and meaning matter:

Ilmuwan menunjukkan lagi reaksi kecil...
→ again (repeating the action of showing)
Ilmuwan lagi menunjukkan reaksi kecil...
→ is currently showing (progressive aspect), not “again”

So if you want the “again” meaning, keep lagi close after the verb menunjukkan.

Why is it reaksi kecil and not kecil reaksi? How do adjectives work here?

In Indonesian, adjectives usually come after the noun:

reaksi kecil = small reaction
rumah besar = big house
tabung kaca = glass tube

Putting the adjective before the noun (kecil reaksi) is generally ungrammatical or at least sounds very strange in standard Indonesian.

So:

reaksi kecil is correct
kecil reaksi is wrong in standard usage

Does di tabung kaca mean “in the glass tube” or “at the glass tube”? Could we use dalam instead of di?

di is a general location preposition meaning at / in / on, depending on context.

In:

reaksi kecil di tabung kaca

it is naturally understood as “in the glass tube”, because reactions occur inside a tube in a lab context.

You sometimes can use dalam (“inside, within”) to emphasize the interior:

reaksi kecil di tabung kaca
= a small reaction in the glass tube (neutral, standard)
reaksi kecil dalam tabung kaca
= a small reaction inside the glass tube (slightly more explicit about “inside”)

Both are generally acceptable, but di tabung kaca is very common and sounds natural.

What does sambil do in this sentence? Could I replace it with ketika or sementara?

sambil means “while (at the same time)”, used when one subject is doing two actions simultaneously:

Ilmuwan menunjukkan lagi reaksi kecil di tabung kaca sambil memakai kacamata pelindung.
The same scientist is (1) showing the reaction and (2) wearing protective glasses at the same time.

Key points:

sambil:
- Same subject for both actions
- Often with an -ing feel: showing… while wearing…
ketika / sementara:
- More like “when / while” introducing another clause
- Often used in more complex sentences, may involve different subjects.

You could say:

Ketika ilmuwan menunjukkan reaksi kecil di tabung kaca, ia memakai kacamata pelindung.
= When the scientist showed the small reaction in the glass tube, he/she wore protective glasses.

But sambil is more compact and natural when you want to highlight one person doing two things at once.

Why is it memakai and not just pakai? Are they different?

The root verb is pakai (“to use / to wear”).

memakai = formal/neutral form with the prefix me-
- Common in writing, narration, and more careful speech
- Ilmuwan memakai kacamata pelindung.
pakai = bare root; very common in informal spoken Indonesian
- Ilmuwan pakai kacamata pelindung. (still fine in everyday speech)

Meaning is basically the same (“to wear” here), but memakai sounds a bit more standard and fits written or narrative style better, like in this sentence.

What exactly does kacamata pelindung mean? Is it singular or plural?

kacamata pelindung literally breaks down as:

kacamata = glasses / spectacles
- from kaca (glass) + mata (eye)
- now written as one word: kacamata
pelindung = protector / protective (thing that protects)

So kacamata pelindung = protective glasses, i.e. safety glasses / goggles.

Number:

Indonesian does not mark singular/plural here:
- kacamata pelindung could be one pair of safety glasses or safety glasses in general.
To be explicit:
- sepasang kacamata pelindung = a pair of safety glasses
- beberapa kacamata pelindung = some safety glasses

In the sentence, context suggests one pair that the scientist is wearing.

How do we know this sentence is past tense (“showed”) if there is no tense marker in Indonesian?

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

shows / is showing (present)
showed / was showing (past)
even will show (future), if the context says so.

Tense is usually indicated by:

time words: kemarin (yesterday), tadi (earlier), besok (tomorrow), etc.
aspect words: sudah (already), sedang (in the middle of), akan (will), etc.

For example:

Tadi ilmuwan menunjukkan reaksi kecil…
= Earlier the scientist showed a small reaction…
Sekarang ilmuwan sedang menunjukkan reaksi kecil…
= Now the scientist is showing a small reaction…

In your isolated sentence, English may translate it as “showed” or “is showing” depending on the surrounding context, which Indonesian itself doesn’t encode in the verb form.

Can we rearrange the sentence, for example moving sambil memakai kacamata pelindung to another place?

Yes, Indonesian word order is fairly flexible for adverbial phrases like this, as long as the meaning stays clear. For example, all of these are acceptable:

Sambil memakai kacamata pelindung, ilmuwan menunjukkan lagi reaksi kecil di tabung kaca.
→ While wearing protective glasses, the scientist showed the small reaction in the glass tube again.
Ilmuwan, sambil memakai kacamata pelindung, menunjukkan lagi reaksi kecil di tabung kaca.
→ Same meaning, slightly more formal or written style.

The core order subject–verb–object (Ilmuwan menunjukkan reaksi kecil...) stays the same. The sambil-phrase can float to the front or after the verb phrase for style or emphasis.

Be careful with lagi though: moving it, as in:

Ilmuwan lagi menunjukkan reaksi kecil...

changes lagi from “again” to “is currently (showing)”, so its position affects the meaning.