Why does volcano have a long vowel sound and volcanic short sound?

It's a great question! You're right to notice that the "o" sound is different in "volcano" and "volcanic." This is due to a phenomenon called vowel reduction.

Here's the breakdown:

* Volcano: The "o" in "volcano" is stressed, making it a long "o" sound. It's pronounced like "voh-l-KAY-noh."

* Volcanic: The "o" in "volcanic" is unstressed, making it a short "o" sound. It's pronounced like "vol-KAN-ik."

Why does this happen?

Vowel reduction is a common feature of English pronunciation. Unstressed vowels often become shorter and less distinct. In "volcanic," the "o" is not the main focus of the word, so it gets reduced to a short "o."

Here are some other examples of vowel reduction:

* Photo: The "o" is stressed, so it's pronounced like "FOH-toh."

* Photograph: The "o" is unstressed, so it's pronounced like "FOH-tuh-graf."

* Atom: The "o" is stressed, so it's pronounced like "AY-tuhm."

* Atomic: The "o" is unstressed, so it's pronounced like "uh-TOM-ik."

It's important to note that these are general trends, and there can be exceptions depending on the specific word. But in the case of "volcano" and "volcanic," the difference in vowel sound is a direct result of stress.