Here's why:
* Short vowels are pronounced quickly and have a short, distinct sound. In "ran," the "a" sound is short and sharp, similar to the "a" in "cat" or "hat."
* Long vowels are typically pronounced longer and have a more drawn-out sound, often with an "e" at the end of the word (like "ran" vs. "rain").
Therefore, the "a" in "ran" has a short vowel sound.