But not so deep as to introduce
a new source of FRICTION."
The Big Bang Theory Season 2, Episode 5
I'm detecting a little FRICTION
between you two,
The Big Bang Theory Season 7, Episode 15
I know that money can
be a source of FRICTION
The Big Bang Theory Season 12, Episode 3
...to static FRICTION between the tire
and the road to zero.
The Big Bang Theory Season 2, Episode 5