Most of the time, vowels keep their short and long sounds. However, sometimes, these vowel sounds change. When this happens, the two letters morph together to make a new sound. Depending on how they morph together, these new sounds could be r-controlled variables, vowel digraphs, and diphthongs. When a vowel is followed by an r, the r changes the way the syllable sounds. These are called r-controlled vowels. This, and a lot more about this concept is shown in this video with brilliant examples which facilitate better understanding and a lasting grip in the students' mind.