The vowel sound in LOOSE is actually shorter than the sound in LOSE. The reason is pre-fortis clipping, a process that causes some consonant sounds to shorten vowels: 

VIDEO: 7 Minutes
QUIZ: 5 Minutes

NOTE: this quiz is about pre-fortis clipping, which is covered in the video above. If you are unfamiliar with the rules, we recommend watching the video before trying the quiz.