I was rereading my student's blogs on the InTune Monthly Magazine article "Let It Slide"
and realized that we hadn't talked about all the different ways you can tune a guitar.
Compare the difference between "Standard" and "Open G" guitar tuning:
(low to high)
Standard Tuning: E A D G B E
Open G Tuning: D G D G B D
Standard tuning produces an unsettled, unresolved chord when strummed. Open G tuning produces a pleasing G major chord when strummed. That's why it and other open tunings are used while playing slide guitar. For more tunings, go to Big City String Company's Guitar Tunings