...caused by relative motion between
the SOURCE of the wave and the observer.
The Big Bang Theory Season 1, Episode 6
So I went back to the SOURCE.
Game of Thrones Season 4, Episode 8
But not so deep as to introduce
a new SOURCE of friction."
The Big Bang Theory Season 2, Episode 5
I know that money can
be a SOURCE of friction
The Big Bang Theory Season 12, Episode 3
as a SOURCE of information
The Big Bang Theory Season 11, Episode 16