Could a weighted ball hung from center of cockpit serve as basic bank indicator? I have always wondered what that string in the windshield of a glider was used for:
https://en.wikipedia.org/wiki/Yaw_string
Got me thinking. If you hung a weighted string from inside the cockpit (centered like an air freshener hung from the rear view of a car) - could that be used as a primitive bank angle indicator? 
What am I not understanding about the physics that would cause the weighted ball to remain perpendicular relative to the aircraft wing - thus making such a device useless?
I'm not sure I fully understand how gyro's solve this problem either - is that missing link?
I have at best a gr. 10 understanding of physics - so please go easy :) 
NOTE: No idea what to tag this question as 
 A: No, this will not work. There are a couple of problems. One is simply that the bob will oscillate, which is inconvenient. That problem can be mitigated by supplying some force of friction that damps out the oscillations.
The other one is fundamental and can't be worked around. One of the basic principles of physics is the equivalence principle, which states that a gravitational field is indistinguishable from an acceleration. Therefore a bob hanging in the cockpit will not actually tell you which way is down. What it will tell you is the difference between the gravitational field vector and the acceleration vector of the aircraft. For example, if a plane is making a turn, the bob will point down and outward, not just down. As a more dramatic example, if you do a loop at high speed, and you're upside-down at the top of the loop, the bob could point up.
This is why gyroscopes are used instead. Passenger jets use ring laser gyros. The gyros have to be initialized when the plane is known to be level and not accelerating.
