Here's why:
* Short vowel sounds are typically quick and sharp, like the sound of "a" in "cat" or "i" in "pig."
* Long vowel sounds are typically drawn out and sound similar to the letter's name, like the sound of "a" in "cake" or "e" in "tree."
The vowel sound in "pan" is similar to the sound of "a" in "cat." It's a short, quick sound.