Why falling camera/objects rotate and then stabilize?

Question

I was going to ask something very similar to this question (which hasn't been answered). Basically a camera fell from an airplane and it began to rotate (maybe because initially it was put in rotation by the hand from which it fell) but then it stabilized! I saw the same phenomena with Felix (the guy from red bull Stratos), though I think the stabilization occurred because of the little-mini-parachute that skydivers use to stabilize their descent.

My question is, does terminal velocity have something to do with this stabilization? GoPro cameras are like a cube, so intuitively, when the cube reaches terminal velocity it will receive the same force throughout the surface that points downwards, if it's not rotating, it will remain stable, if it is rotating how does this "uniform" force over the rigid body stabilize it?

I appreciate your thoughts on the problem.

Answer 1

An object with corners or longer in one dimension than in the others, can fall on such a part and be in unstable equilibrium. E.g. an object touches the ground on one of its corners but the center is not on the vertical that passes through that corner. That generates a torque, and angular momentum appears that tends to be conserved.

Answer 2

It this case the overwhelming factor is aerodynamics. You have seeds that essentially hit terminal velocity very quickly, but spin the whole way (which keeps them spinning). When you skydive, a small asymmetry will induce a spin which will get faster and faster if not corrected.

Also, objects go through different regimes depending on speed and humidity, which makes them behave differently. For example in cricket, some bowlers are able (when various climatic conditions such as humidity and pressure, as well as age of ball) to get "reverse swing". In this case, normal swing occurs for the first half of the ball's travel (making the ball swing or curve laterally in the air), and then reverse and swing the other way for the second half of the ball's travel, when the ball has slowed slightly. In other words, the ball makes an S shape when viewed from above.

These kind of factors mean that the surface details and geometries and even relative pressure and humidity will all play a part in how the object reacts. Other things being equal, it will tend to get the heavy parts down. Which is why skydivers often arch (to go stomach first), and a beer belly is considered an advantage.

To speculate about the phenomenon you observed, likely the object was given some initial angular momentum, but perhaps not in the direction that aerodynamics would push it. As a consequence it stabilised the initial rotation, and may have begun a different rotation given time.