Why is an Attitude Indicator not Built Like a Ball Compass?

[greypilgrim]

Hi.
I used to think that the attitude indicators (artificial horizons) in airplanes were just bottom-heavy spheres swimming in a liquid in a transparent shell, like a ball compass:

But apparently they use quite a complicated gyroscopic system. Why?

 

[Lnewqban]

As the aircraft deviates from a rectilinear trajectory, it induces centripetal forces that would affect the bottom-heavy sphere, because of which its weight vector would deviate from a purely vertical direction, misleading the pilot.

Please, see:
https://en.wikipedia.org/wiki/Spatial_disorientation

https://en.wikipedia.org/wiki/Banked_turn#Banked_turn_in_aeronautics

 

[DaveC426913]

Right. Of course.

In a banking turn, "down" is no longer down.