I have been trying to get a wrecking ball to collide with an upright slab of jello, with no success so far. I've tried so many combinations of physics attributes that I can't remember them all, but so far I have achieved only 2 main types of result: 1) the wrecking ball hits the jello slab and is stopped dead, 2) the wrecking ball goes right through the jello slab. What I expected: the slab would cave in at the impact point, quiver and wobble, and be hurled backwards.
I believe the jello slab is more or less correct because I drop it a short distance at start of sim and it compresses and bounces back convincingly. So I think there is something about collisions between RB objects and SB objects that I'm not understanding. Can someone point me at the tute or example that I have not yet found by googling?
UPDATE: One way to do it (sorta): create a rigid body. Then add Soft Body to it and proceed to tweak. https://www.flickr.com/photos/rootlessagrarian/31909036596 I hope that link is visible to others. Anyway, as (I hope) you can see it is semi-successful, but the "jello mattress" continues to have a life of its own after impact, slithering towards the edge of the floor and remaining obstinately dimpled in places even though Plastic was set to 0. Also, the observant viewer will notice that the wrecking ball and chain actually penetrate the surface on impact :-( but it's the best I have managed thus far. I did try making the wrecking ball a very stiff Soft Body, but then of course it wouldn't stick to the chain... I'd have had to redo the entire chain.
Here is another probably final attempt with even stranger physics. In this one I went back and adjusted centre of mass for the wrecking ball, made sure to Apply all Scales, and gave the jello mattress a plinth so it could be knocked off.
I have no idea why it is hesitating on its way to the floor... suggestions welcome, though I may soon give up on trying to make these two species of object interact and move on to learning more about things that Blender wants to do rather than trying to make it do things it doesn't like.