Here's why:
* Short vowel sounds are typically quick and sharp. They are the sounds you hear in words like "cat," "bed," "dog," and "sun."
* Long vowel sounds are typically drawn out and are often spelled with a vowel followed by a silent "e" or a vowel digraph (two vowels together).
The "a" in "can" has a short, sharp sound similar to the "a" in "cat."