writing accents

what is the rule for writing accents in Hiragana? why is the u character written for an accented o, when every other vowel seems to use its own character? thanks

くうこう

kūkō

こんにちは (Konnichiwa) Paolo-xy6b,

Thanks for your question!

In Japanese, whenever an お (o) vowel sound is followed by an う (u) vowel sound, the う (u) vowel sound that follows is pronounced as an お (o) sound (despite being written as う (u)). In other words, whenever you see a word with an お (o) and う (u) vowel sound combination, this will be pronoucned as one long お (o) vowel sound. For example:

Since rōmaji serves as a reading aid, the macron ("-")over the “o” makes the most sense when it comes to explaining how this word is pronounced (that is, as an elongated お (o) sound). 

Japanese has various romanization systems, though, so you may see this romanized in different ways depending on the resource you're looking at. For the word くうこう (kūkō) “airport” for example, you may see the following variations:

kuukou

kūkou

kūkō

kuukō

Learning to read katakana and hiragana can help to mitiagte the confusion that sometimes comes from reading romanizations. 

I hope this helped!

べんきょう　を　がんばって　ください！ (Benkyō o ganbatte kudasai!)

I think I understand. 

Also, can you tell me why the “ja” sound is written using じ (ji) and ゃ(ya)?

Thanks for your help.

こんにちは  (Konnichiwa) Paolo-xy6b,

The reason for this is because the  じ (ji) and や (ya) sounds join together to make the sound “ja."

Some sounds in Japanese can only be made by joining two syllables together; these are known as “ combination syllables.” In combination syllables, the sound of the the two individual syllables join together to form a single sound. Combination syllables are made by adding a small や (ya), ゆ (yu), or よ (yo) character after a consonant. The sound じゃ (ja) is an example of a combination syllable: it combines the syllables じ (ji) and や (ya) together. 

To answer your question a little more specifically, in combination syllables, the vowel sound disappears from the consonant and the “y” sound disappears from the や (ya), ゆ (yu), or よ (yo) syllable. In the case of じゃ (ja), the vowel sound “i" disappears from the じ (ji) and the “y” sound disappears from や (ya) so that together, we get a “ja” sound. 

You can learn more about combination syllables in this Writing lesson:
https://app.rocketlanguages.com/members/products/5/lesson/5201#top

I hope this helped! 
べんきょう　を　がんばって　ください！ (Benkyō o ganbatte kudasai!)

Thank you!