So I dropped the new iPhone X down a 4000+ ft. deep mine hole and recorded it all to see what happens.
So here's how my experiment went down. The fishing line I bought was 1329 yards (3987 ft.) When the line ran out I was pretty disappointed thinking it's just dangling but the iPhone footage shows it seems to have hit something.
I assume the line just kept unraveling despite the phone landing, unless it just landed on a ledge or something and actually was 4000 feet deep? Hard to tell but after the initial 2-3 second drag delay, the iPhone was going down pretty fast and for like a good three minutes.