Щоразу, коли колесо рухається, спиця торкається світловідбивача.

Yes, щоразу is written as one word. It means every time or each time.

In this sentence, Щоразу, коли... means Every time when..., which English would usually shorten to just Whenever... or Every time....

A very close alternative is кожного разу:

• Щоразу, коли колесо рухається...
• Кожного разу, коли колесо рухається...

Both are natural. Щоразу is just more compact.

The commas mark off the clause introduced by коли.

The structure is:

• Щоразу, коли колесо рухається, спиця торкається світловідбивача.

Literally:

• Every time, when the wheel moves, the spoke touches the reflector.

In Ukrainian, subordinate clauses are usually separated by commas. Here коли колесо рухається is a time clause, so it is set off with commas.

You can think of the sentence as:

• Main idea: спиця торкається світловідбивача
• Time condition: коли колесо рухається
• Framing expression: щоразу

Because колесо is the subject of рухається.

• колесо рухається = the wheel moves / is moving

In Ukrainian, the subject of a sentence is normally in the nominative case.
Here:

• колесо = nominative singular, wheel
• рухається = moves

So this part literally means the wheel moves.

Рухається means moves or is moving.

It comes from рухатися = to move.

The ending -ся is a very common Ukrainian verb ending. It often makes the verb reflexive or changes how the action is understood. In many verbs, especially motion/state verbs, it is simply part of the normal dictionary form and has to be learned with the verb.

So:

• рухати = to move something
• рухатися = to move oneself / to be moving

That is why:

• колесо рухається = the wheel moves

Because Ukrainian often uses the present tense for actions that happen regularly, generally, or whenever a condition is met.

This sentence describes a repeated or habitual fact:

• Every time the wheel moves, the spoke touches the reflector.

So the present tense here does not mean only right now. It can also mean:

• something that happens regularly
• a general truth
• a repeated mechanical action

English does this too:

• When water boils, it evaporates.
• Every time the wheel moves, the spoke touches the reflector.

Because the verb торкатися normally takes the genitive case, not the accusative.

So:

• dictionary form: світловідбивач = reflector
• in this sentence: світловідбивача = genitive singular

That is because:

• торкатися чого? = to touch what?
  The answer goes in the genitive.

So:

• спиця торкається світловідбивача = the spoke touches the reflector

This is one of those verb patterns that learners usually just have to memorize.

Торкатися and торкати are related, but торкатися is the normal verb for to touch in this kind of sentence.

Here:

• торкається = from торкатися
• it means touches

The important thing for a learner is:

• торкатися is very commonly used with the genitive case
• that is why you get світловідбивача

So in this sentence, торкається is the expected choice.

Not necessarily. Ukrainian often uses the singular when talking about a typical repeated action involving one item at a time.

Here the idea is something like:

• a spoke touches the reflector
• or the spoke touches the reflector

It is describing what happens in the wheel’s rotation: one spoke comes around and makes contact.

So the singular sounds natural because the sentence is describing the event as a repeating mechanical pattern, not necessarily talking about all spokes at once.

Світловідбивач is a compound word:

• світло = light
• відбивати / відбивач = to reflect / reflector-like formation

So світловідбивач literally means something like light-reflector, i.e. reflector.

This kind of compound word is common in Ukrainian technical or descriptive vocabulary.

Yes, Ukrainian word order is more flexible than English word order, although not completely free.

The given sentence is neutral and clear:

• Щоразу, коли колесо рухається, спиця торкається світловідбивача.

You could also rearrange parts for emphasis, for example:

• Спиця торкається світловідбивача щоразу, коли колесо рухається.

That still means the same thing. The difference is mostly stylistic or about what you want to emphasize first.

For learners, the original order is a very good standard pattern:

• time expression first
• then the main action

Yes, but the meaning changes slightly.

• Коли колесо рухається, спиця торкається світловідбивача.
  = When the wheel moves, the spoke touches the reflector.

• Щоразу, коли колесо рухається, спиця торкається світловідбивача.
  = Every time the wheel moves, the spoke touches the reflector.

Without щоразу, the sentence still works, but щоразу makes the idea of repetition more explicit: each time this happens.

Because Ukrainian has no articles.

English distinguishes:

• a wheel
• the wheel

Ukrainian simply says:

• колесо

The exact meaning depends on context. In this sentence, English might translate the nouns as:

• the wheel
• the spoke
• the reflector

because the situation sounds specific. But Ukrainian does not need separate words for that.

It describes a repeated process or a general mechanical fact.

Several things show that:

• щоразу = every time
• коли clause = repeated condition
• present tense verbs = habitual/general action

So the sentence is not about one single moment. It means that whenever this condition happens, the result happens too.

A very useful way is:

• Щоразу = every time
• коли колесо рухається = when the wheel moves
• спиця торкається = the spoke touches
• світловідбивача = the reflector

So the full pattern is:

• Щоразу, коли X, Y.
• Every time X, Y.

That makes it easier to reuse:

• Щоразу, коли я читаю, я засинаю.
• Every time I read, I fall asleep.

The sentence you were given follows that exact pattern.