Pentatonic scale

Hey guys. I see that pentatonic scales a minor and c major have the same notes. So do you determine which scale it is by where you start or what. I read that minor scales have a sadder sound, but how would the sound differ from a major scale if the notes are the same?

It's all in the tonic. You have a predominant sound when you play the notes of one scale in this order, instead of another.
You determine the key from what notes seem to be focus point. As you pointed out, if you hear a sad song and know it's using the pentatonic scales there is a good chance it's in minor. The scale starts on a specific note, the tonic, but when creating music, it doe not have to be the first or last note played, but it will have some pull.
If you know the music, you can look into the other notes being played to find clues as to what the scale is.

A minor is the relative minor to C major which means that it is the aeolian mode (or sixth mode) in the key of C major and therefore contains the same notes. you can also find relative minors by counting three half steps back from the major root.