Here's why:
* Short vowel sounds are typically quick and sharp, often represented by the single letter vowel in a word (e.g., "u" in "duck").
* Long vowel sounds are often represented by a vowel followed by a silent "e" or by a vowel combination (e.g., "u" in "flute" or "ue" in "due").
Therefore, the "u" sound in "duck" is a short vowel sound, distinct from the longer "u" sound in words like "flute" or "cute."