I don't know what you mean with "flat side". But if two black holes collide, this should produce a huge amount of gravitational wave. This is believed to be a common result of galaxy mergers.
There are six flat sides
There are 2 completely flat sides on every cylinder.
square
So that whatever leftover gunk happens to be on the table doesn't get all over the part of the stopper that goes into the bottle, contaminating the contents.
A triangle has three sides !
Faces are sides but sides (as in sides of a square) need not be faces.
A pentagon has five flat sides
It is a pyramid.
Trapezoid.
If it has flat sides it will influence the spin characteristics, possibly causing it to become unstable.
It is. All sides of a geometric pyramid are flat - even stepped pyramids.
plumage