The o-vowel changes its sound slightly depending on whether it is spoken short or long.
The short "o" sounds open, the lips are more relaxed, the lower jaw drops slightly.

The long "o" sounds more closed; the mouth is more closed, the lips are more puckered.

Click "play all", then you will hear 3 short and 3 long "o"s spoken.

Later you can check out the translations in the mouse-overs.