Here's why:
* Short vowel sounds are typically quick and sharp. They often sound like the first letter of the vowel's name (e.g., "a" in "cat," "e" in "bed," "i" in "pig," "o" in "hot," "u" in "cup").
* Long vowel sounds are usually longer and smoother, often sounding like the vowel's full name (e.g., "a" in "cake," "e" in "see," "i" in "kite," "o" in "go," "u" in "flute").
In "sock," the "o" sound is short and sharp, similar to the sound of "o" in "hot."