Sidesømmen må flyttes.

Because Norwegian usually writes compound nouns as a single word.

• side = side
• søm = seam
• sidesøm = side seam

Then the definite ending is added to the whole compound:

• en sidesøm = a side seam
• sidesømmen = the side seam

This is very normal in Norwegian. English often uses two words where Norwegian uses one.

-en is the definite singular ending for many masculine nouns in Bokmål.

So:

• en sidesøm = a side seam
• sidesømmen = the side seam

Unlike English, Norwegian usually puts the definite article at the end of the noun instead of using a separate word like the.

Sidesøm is masculine in Bokmål, so its basic forms are:

• en sidesøm = a side seam
• sidesømmen = the side seam
• sidesømmer = side seams
• sidesømmene = the side seams

In compounds, the gender usually comes from the main final noun, which here is søm.

Må is the present tense of å måtte, and it expresses necessity, like must or has to in English.

So in this sentence it shows that moving the side seam is necessary.

A useful thing to remember: Norwegian verbs do not change form depending on the subject.

• jeg må
• du må
• han må
• vi må

It is always må.

Because modal verbs like må, kan, skal, vil, and bør normally take an infinitive without å.

Compare:

• Jeg vil flytte den.
• Sidesømmen må flyttes.

So after må, you do not say å flyttes.

Because flyttes is passive.

• flytte = to move something
• flyttes = be moved

In this sentence, the side seam is not doing the action; it is receiving the action. That is why Norwegian uses the passive form.

So:

• Vi må flytte sidesømmen. = We must move the side seam.
• Sidesømmen må flyttes. = The side seam must be moved.

It looks like the present passive form, but after a modal verb such as må, it works like a passive infinitive in meaning.

So learners should understand:

• må flyttes = must be moved

not

• must is moved

In other words, after må, think of flyttes here as part of the idea be moved.

Yes. It is a passive sentence.

The active version would be something like:

• Noen må flytte sidesømmen. = Someone must move the side seam.

The passive version removes or hides the person doing the action:

• Sidesømmen må flyttes.

This is very common in instructions, technical writing, sewing patterns, manuals, and workplace language, where the action matters more than who does it.

Yes, you could. That is also correct.

There are two common ways to form the passive in Norwegian:

• s-passive: må flyttes
• bli-passive: må bli flyttet

In many cases both are possible. In short practical instructions, må flyttes often sounds neat and natural. Må bli flyttet can sound a bit more explicit or a bit heavier.

So both work, but må flyttes is very typical in this kind of sentence.

Because Norwegian main clauses follow the verb-second rule.

The finite verb here is må, and it must come in the second position in the clause.

So with the subject first:

• Sidesømmen må flyttes.

If you start with another element, the verb still stays second, and the subject moves after it:

• Nå må sidesømmen flyttes.
• I morgen må sidesømmen flyttes.

This verb-second pattern is one of the most important word-order rules in Norwegian.

Ø does not have an exact English equivalent, so it often takes practice.

A rough guide:

• keep your tongue somewhat like for e in bed
• round your lips

For many learners, a rough approximation is something a bit like the vowel in British English bird without a strong r, but that is only approximate.

So søm has a rounded vowel that is different from both o and e. It is worth practicing because ø is a very common Norwegian sound.