Hi，everybody. I am a beginner to learn the motion simulation. I have done some the official exercises, but had some unsolve problems.Such as：

1.Why are the two face even an intrusion or separation，even if i have defined the contact cooperation(problem1).

2.I have defined some tasks, the eighth shows very special, it has two moves(extended and retracted),but first time it's just entended,not retracted, the second time is normal. I don't know why(problem 2)?

Thanks for your any replies.