Here's why:
* Short vowel sounds are typically found in words where the vowel is followed by one consonant. In "wag," the "a" is followed by the consonant "g."
* Long vowel sounds are often found in words where the vowel is followed by a consonant and a silent "e" at the end, or where the vowel is part of a vowel digraph (two vowels that make one sound).
The sound of "wag" is similar to the short "a" sound in words like "cat," "hat," and "bag."