Ytan känns kall.

Because ytan is the definite singular form of yta.

• yta = a surface
• ytan = the surface

In Swedish, the idea of the is often added as a suffix to the noun instead of being a separate word. So ytan already includes the.

It is an en word: en yta.

That matters for agreement and for the definite form:

• en yta = a surface
• ytan = the surface
• ytor = surfaces
• ytorna = the surfaces

Because it is an en word, a predicative adjective in the singular will usually take the common gender form, which is why you get kall rather than kallt.

Känns is the present tense of kännas, which is an s-verb in Swedish.

The basic forms are:

• kännas = to feel / seem
• känns = feels / seems
• kändes = felt / seemed

In this sentence, känns means something like feels or seems to the touch.

Even though -s often reminds learners of the passive, here it is best to learn kännas as its own verb.

This is a very common question.

• känna often means to feel, sense, know, recognize
• kännas means to feel / seem from someone's point of view

Compare:

• Jag känner något kallt. = I feel something cold.
• Ytan känns kall. = The surface feels cold.

So in Ytan känns kall, the subject is the surface, and the sentence describes how it seems to a person who touches or experiences it.

Because kall agrees with ytan, which is singular and common gender.

Swedish adjective agreement here works like this:

• common gender singular: kall
• neuter singular: kallt
• plural: kalla

So:

• Ytan känns kall. = common gender singular
• Golvet känns kallt. = neuter singular
• Ytorna känns kalla. = plural

Because kall is being used predicatively, not attributively.

In Ytan känns kall, kall comes after the verb and describes the subject. Predicative adjectives agree in gender and number, but not in definiteness.

Compare:

• den kalla ytan = the cold surface
  Here the adjective comes before the noun, so it takes the definite/plural-style form kalla.

• ytan känns kall = the surface feels cold
  Here the adjective comes after the verb, so it stays kall.

This difference is very important in Swedish.

Because känns and är are not exactly the same.

• Ytan är kall. = The surface is cold.
  This sounds more like a direct statement of fact.

• Ytan känns kall. = The surface feels cold.
  This focuses on how it seems or feels, usually to the touch.

So känns is often a little more subjective or based on sensory experience.

Yes. Swedish often leaves that unstated.

Ytan känns kall naturally means that the surface feels cold to the person experiencing it. English does the same thing in many cases.

If you really want to mention the experiencer, you can add it, for example:

• Ytan känns kall för mig. = The surface feels cold to me.

But in most everyday situations, that extra part is unnecessary.

You can do it like this:

• Ytan känns inte kall. = The surface does not feel cold.
• Känns ytan kall? = Does the surface feel cold?

In the question, Swedish puts the verb first: Känns ytan kall? This is normal Swedish word order for yes/no questions.