3 Possibilities:
1. You didn't set the entityradius correctly (use for the sphere collision)
2. Your gravitiy is to high, the object just teleports through the ground
3. You might have renderworld but forgot to call updateworld, which is needed for this.
1. You didn't set the entityradius correctly (use for the sphere collision)
2. Your gravitiy is to high, the object just teleports through the ground
3. You might have renderworld but forgot to call updateworld, which is needed for this.