Here's why:
* Diphthong: A diphthong is a sound made by combining two vowel sounds within a single syllable. The sound glides from one vowel to the other.
* Double "oo" sound: The double "oo" sound, as in "moon" or "food," is a gliding sound that starts with a more open vowel sound and moves towards a more closed vowel sound.
Examples:
* "moon" - The "oo" sound starts with a sound similar to the vowel in "mood" and transitions to a sound closer to the vowel in "foot."
* "food" - The same transition happens in "food," from a more open "oo" to a more closed "oo."
Short vowels and long vowels:
* Short vowels are single, distinct sounds, like the "a" in "cat" or the "i" in "bit."
* Long vowels often correspond to the vowel sound in the word's spelling, like the "a" in "bake" or the "e" in "be."
Therefore, while the "oo" in words like "moon" and "food" may be a long vowel sound, it's actually formed by a diphthong, not a single vowel sound.