Learn Hardcore Swahili: Tukiweka sumaku karibu na simu, mara nyingine ishara ya mtandao hupotea. - If we put a magnet near the phone, sometimes the network signal disappears.

So tukiweka literally means when we put or if we put. It describes an action that happens at the same time as, or as a condition for, the main clause.

In this sentence, Tukiweka sumaku karibu na simu = When we put a magnet near the phone / If we put a magnet near the phone.

What does the -ki- marker (in tukiweka) do, and how is it different from normal present tense?

The -ki- marker links two actions and usually means when, while, or sometimes if. It is used in the dependent clause (the first part of the sentence here):

Tukiweka sumaku karibu na simu = When/If we put a magnet near the phone...

Compare:

Tunaweka sumaku karibu na simu. = We are putting / we put a magnet near the phone. (simple present, no condition)
Tukiweka sumaku karibu na simu, ... = When/If we put a magnet near the phone, ... (sets up a condition or time frame)

So -ki- is not just a tense; it connects two clauses: “when/if X happens, Y happens”.

Could we say Tunapoweka sumaku karibu na simu instead of Tukiweka sumaku karibu na simu? What is the difference between -ki- and -napo-?

Yes, you can say:

Tunapoweka sumaku karibu na simu, mara nyingine ishara ya mtandao hupotea.

Both tukiweka and tunapoweka can mean when we put.

Subtle differences:

-ki- (tukiweka) often feels a bit more general or typical:
- Tukiweka sumaku karibu na simu, ... = In general, when/if we put a magnet near the phone, this can happen.
-napo- (tunapoweka) tends to emphasize whenever / the times when in a slightly more specific or ongoing sense:
- Tunapoweka sumaku karibu na simu, ... = Whenever we put a magnet near the phone, ... (still general, but can feel a bit more “each time we do it”)

In everyday speech, both forms are acceptable here, and many speakers would use them almost interchangeably.

Does tukiweka here really mean “we”, or can it be understood more like “when you put / when one puts”?

Grammatically, tukiweka = when we put (tu- = we).

However, in Swahili, “we” can often be used in a general, inclusive way, much like English “you” or “one” in general statements:

Tukiweka sumaku karibu na simu, ...
can be understood as
When you put a magnet near the phone, sometimes the signal disappears.

So it doesn’t necessarily mean “we (specific people sitting here)”, but more like “people in general / you in general”.

What is sumaku? Is it singular or plural? Does it change form in the plural?

Sumaku means magnet.

It belongs to a noun class where the singular and plural look the same (class 9/10). So:

sumaku = a magnet / magnets (context decides)

Examples:

Nina sumaku moja. = I have one magnet.
Nina sumaku tatu. = I have three magnets.

There is no separate plural form like masumaku; sumaku is used for both singular and plural.

What does karibu na mean, and how is it different from just karibu?

Karibu has several uses:

As an adverb:
- Yuko karibu. = He/She is near.
  (No object mentioned.)
As a preposition-like phrase with na:
- karibu na = near / close to (something)
- karibu na simu = near the phone
As a greeting:
- Karibu! = Welcome! (come in, feel at home)

In this sentence, karibu na simu specifically means near the phone.

You cannot say *karibu simu for “near the phone”. You need na:
karibu na + [noun] = near [noun].

What does mara nyingine mean, and how is it different from wakati mwingine?

Mara nyingine literally means other times, and in practice it usually means sometimes.

In this sentence:

mara nyingine ishara ya mtandao hupotea
= sometimes the network signal disappears.

Wakati mwingine also means sometimes or another time. The nuance:

mara nyingine – focuses on occasions or instances (“other times, on some occasions”)
wakati mwingine – focuses on time/periods (“at other times, sometimes”)

In many contexts they are interchangeable:

Mara nyingine naenda kwa miguu. = Sometimes I go on foot.
Wakati mwingine naenda kwa miguu. = Sometimes I go on foot.

Here, you could also say Wakati mwingine ishara ya mtandao hupotea, with the same meaning.

What exactly does ishara ya mtandao mean?

Breakdown:

ishara = signal, sign, indicator
mtandao = network, often also internet (literally “something spread out / network”)

So ishara ya mtandao means network signal. In the context of a phone, this is the mobile network signal (like the bars of reception).

So the full clause:

mara nyingine ishara ya mtandao hupotea
= sometimes the network signal disappears (you lose reception).

Why is it ishara ya mtandao and not ishara wa mtandao? What is the role of ya here?

The word ya is the possessive/connecting word (the -a construction) agreeing with the noun class of ishara.

ishara belongs to noun class 9/10, whose -a connector form is ya.
mtandao is the noun it is linked to (of the network).

So:

ishara ya mtandao = signal of the network / network signal

If the head noun were in a different class, the connector would change. For example:

mtaro wa mtandao = the trench of the network (class 3, connector wa)
vitabu vya Kiswahili = Swahili books (class 8, connector vya)

Here, ishara → class 9/10 → connector ya → ishara ya mtandao.

What does hupotea mean, and how is hu- different from ina- (like inapotea)?

The verb is kupotea = to disappear / to be lost.

Hupotea is made of:

hu- (special prefix)
-potea (verb stem)

The hu- prefix is used for habitual / general truth in the 3rd person (he/she/it/they/it in general). It often translates as usually / tends to / (generally) does.

So:

ishara ya mtandao hupotea
= the network signal (sometimes) disappears / tends to disappear (as a general occurrence).

Compare:

ishara ya mtandao inapotea.
- ina- is normal present: “is disappearing / disappears (now / this time).”
  This can refer more to a specific situation happening now.
ishara ya mtandao hupotea.
- points to what usually or sometimes happens in general, not just this moment.

In this sentence, hu- fits well because the whole sentence describes a typical or possible effect of putting a magnet near a phone, not one specific event.

Can the order of the clauses be changed? For example: Mara nyingine ishara ya mtandao hupotea tukiweka sumaku karibu na simu.

Yes, you can reverse the order:

Tukiweka sumaku karibu na simu, mara nyingine ishara ya mtandao hupotea.
Mara nyingine ishara ya mtandao hupotea tukiweka sumaku karibu na simu.

Both mean the same thing. The difference is emphasis:

Starting with Tukiweka sumaku... emphasizes the condition first.
Starting with Mara nyingine ishara... emphasizes the result (sometimes the signal disappears) first.

The comma after the first clause is optional in everyday writing, but it can help readability, especially when the -ki- clause comes first.

Could we say sumaku karibu simu without na, or is na necessary?

In this structure, na is necessary.

karibu na [noun] = near [noun], close to [noun]
karibu na simu = near the phone

You cannot drop na here:

*karibu simu is not correct for “near the phone.”

So the correct form is sumaku karibu na simu = a magnet close to the phone / a magnet near the phone.

Does simu mean specifically a mobile phone, or any kind of phone?

Simu is a general word for telephone. It can mean:

a mobile phone (cell phone)
a landline phone
a phone call in some contexts (e.g. Nimepata simu = I got a call)

Context usually tells you what kind of phone. In modern everyday speech, simu very often refers to a mobile phone, since that is what people mostly use.