natu ha atui node, kami wo mizikaku simasu.

は marks the topic of the sentence.

So 夏は means something like as for summer or when it comes to summer. The sentence is talking about what happens in the context of summer.

It is not the same as saying summer is performing an action. It just sets the frame for the statement:

• 夏は暑い = Summer is hot / As for summer, it’s hot

ので is a grammar pattern meaning because, since, or so.

Here:

• 暑い = hot
• 暑いので = because it is hot

You cannot normally use で by itself after an い-adjective like 暑い to mean because.

So:

• 暑いので、髪を短くします。 = Because it’s hot, I make/cut my hair short.

Both can mean because, but the nuance is a little different.

• ので sounds a bit more explanatory, softer, and less direct
• から can sound a bit more straightforward or assertive

So:

• 夏は暑いので、髪を短くします。
• 夏は暑いから、髪を短くします。

Both are natural, but ので often feels slightly more polite or matter-of-fact.

を marks the direct object of the verb.

In this sentence, 髪 is the thing being changed:

• 髪を短くします = make/cut the hair short

Even though in English we might think of short as the important part, in Japanese the hair itself is still treated as the object of the action.

This comes from the い-adjective 短い meaning short.

To use an い-adjective before a verb like する, you change -い to -く:

• 短い → 短く

Then:

• 短くする = to make something short

So:

• 髪を短くします = I make my hair short = I cut my hair short

This pattern is very common:

• 部屋を明るくする = make the room bright
• 値段を安くする = make the price cheap/lower the price

Good question. Both are possible, but they focus on slightly different things.

• 髪を切ります = cut hair
  Focus: the action of cutting

• 髪を短くします = make hair short / cut hair short
  Focus: the resulting state

So this sentence emphasizes the result: the hair becomes short.

In real life, people also say:

• 夏は暑いので、髪を短く切ります。 = Because summer is hot, I cut my hair short.

It can mean either, depending on context.

• make my hair short
• cut my hair short
• shorten my hair

Japanese does not always specify whether the final result is simply shorter than before or specifically short in an absolute sense. Context usually tells you.

So in natural English, this sentence is often translated as:

• Because summer is hot, I cut my hair short.

The subject is omitted, which is very common in Japanese.

A full version could be:

• 私は夏は暑いので、髪を短くします。

But Japanese often leaves out 私 if it is obvious from context.

In a standalone sentence like this, the most natural assumption is:

• I cut my hair short because summer is hot

Depending on context, it could also mean she/he/they do this, but without context learners usually read it as I.

Japanese non-past forms often cover both present and future, and sometimes habitual actions too.

So 髪を短くします could mean:

• I cut my hair short (habitually / generally)
• I will cut my hair short (future plan)
• I am going to cut my hair short (depending on context)

With 夏は暑いので, the sentence often sounds like a general or repeated habit:

• Because summer is hot, I cut my hair short.

But it could also refer to a current decision:

• Since summer is hot, I’m going to cut my hair short.

夏は sets up summer as the topic: as for summer.

Using に would not be natural here, because に usually marks a specific time when something happens. But 暑い is a general description of summer, not a one-time event happening at summer.

So:

• 夏は暑い = Summer is hot
  is natural.

You could use 夏に in sentences like:

• 夏に髪を短くします。 = I cut my hair short in summer.

There, 夏に marks the time of the action する.

The comma helps separate the reason from the main action:

• 夏は暑いので、 = Because summer is hot,
• 髪を短くします。 = I cut my hair short.

In Japanese, commas are often used for readability and rhythm. In a sentence like this, the comma is very natural, though punctuation can vary a little depending on writing style.

No. Normal Japanese is usually written without spaces.

So this sentence would normally appear as:

• 夏は暑いので、髪を短くします。

The spaced version is just for learners, to make the parts easier to see:

• 夏 / は / 暑い / ので / 髪 / を / 短く / します

Yes, but the meaning changes.

• 髪を短くします = I make/cut my hair short = someone intentionally changes it

• 髪が短くなります = My hair becomes short = focuses on the change itself, not on the person doing it

So in your sentence, する is used because the speaker is intentionally doing something to the hair.