Педаль торкається ланцюга.

Because the verb торкатися requires the genitive case, not the accusative.

So:

• ланцюг = nominative singular, chain
• ланцюга = genitive singular, of the chain / the chain after this verb

This is something English speakers often have to get used to: some Ukrainian verbs simply govern a different case than you might expect from English.

So in this sentence:

• Педаль = the subject
• торкається = touches / is touching
• ланцюга = the object in the genitive, because торкатися takes genitive

Торкається is the 3rd person singular present tense form of торкатися.

Breakdown:

• торкатися = to touch
• торкається = he/she/it touches, is touching

Since педаль is singular, the verb is also singular.

So literally:

• Педаль торкається ланцюга = The pedal touches the chain

The -ся is a very common Ukrainian verb ending often called the reflexive marker. But it does not always mean a truly reflexive action like wash oneself.

In торкатися, the -ся is just part of the standard dictionary form of the verb meaning to touch.

So you should learn it as a whole unit:

• торкатися = to touch

not as:

• торкати
  • something extra you can ignore

For learners, the safest approach is to memorize торкатися together with the case it needs:

• торкатися + genitive

Yes, педаль is feminine.

In Ukrainian, many feminine nouns end in a soft sign (ь). These are typically feminine nouns of the so-called third declension.

So:

• педаль = feminine singular noun

That is why, if you used an adjective with it, the adjective would be feminine:

• ліва педаль = the left pedal

Педаль is in the nominative singular because it is the subject of the sentence.

The sentence structure is:

• Педаль = subject, nominative
• торкається = verb
• ланцюга = object required by the verb, genitive

So even though English speakers may expect the chain to be in a direct-object case like the accusative, Ukrainian uses genitive here because of the verb.

It can mean either, depending on context.

The Ukrainian present tense often covers both:

• The pedal touches the chain
• The pedal is touching the chain

So without extra context, торкається can describe:

1. a general fact or recurring situation, or
2. something happening at the moment

If you want to make right now clearer, Ukrainian often adds an adverb or context:

• Зараз педаль торкається ланцюга. = Right now the pedal is touching the chain.

Yes. That is an aspect difference.

• торкатися = imperfective, ongoing/repeated/general touching
• торкнутися = perfective, a single completed touch

Examples:

• Педаль торкається ланцюга. = The pedal touches / is touching the chain.
• Педаль торкнулася ланцюга. = The pedal touched the chain.
• Педаль торкнеться ланцюга. = The pedal will touch the chain.

This is a very common Ukrainian verb pair:

• торкатися / торкнутися

Yes. Ukrainian word order is more flexible than English.

The neutral order here is:

• Педаль торкається ланцюга.

But other orders are possible for emphasis, for example:

• Ланцюга торкається педаль.
  This puts more focus on the chain.
• Торкається ланцюга педаль.
  This can sound more marked or stylistic.

For most learners, the basic subject + verb + object order is the safest choice.

A rough pronunciation guide:

• Педаль ≈ peh-DAHL’
• торкається ≈ tor-KA-ye-tsya
• ланцюга ≈ lan-tsyu-HA

A few useful notes:

• ль in педаль is soft
• є in -кається sounds like ye
• г in Ukrainian is usually a softer sound than English g, closer to a voiced h

So the whole sentence sounds roughly like:

• peh-DAHL’ tor-KA-ye-tsya lan-tsyu-HA

Yes, you may encounter доторкатися / доторкнутися, which also means to touch.

Very roughly:

• торкатися = to touch
• доторкатися = to make contact with, to touch

In many contexts they are quite close, but торкатися is perfectly normal here.

For a beginner, the key thing is that both verbs are commonly used with the genitive:

• торкатися ланцюга
• доторкатися ланцюга

Yes. Ланцюг is the standard Ukrainian word for chain.

In this sentence it becomes ланцюга because of the verb:

• dictionary form: ланцюг
• in the sentence: ланцюга

This is a good example of why it helps to learn nouns both in their base form and in common case forms.