Dear expert. 

I don't quite understand the difference between

1. Velocity at Boundary condition - not available for initial step

 2. Velocity at Pre-defined Filed:    Initial step only

As far as I understand, the only difference is availability on step. 

I am modelling rolling steel ball (9mm) inside tube.

ball is unforced, free movement with initial speed v. Ball hit the rubber wall and should bounce 

The problem is that ball does not bounce but keep pushing the wall. 

I tested velocity for boundary condition and Pre-defined Field.

Help please. 

Gunmo Gu