collision without rigidbody

I have a cube A without rigidbody. I try to use it to collide the other cube B which has a rigidbody.
When Cube A moves from bottom to top, it always hits cubeB. But if you put the cube B on the plane and let the A level hit, if A hits it fast, it will hit B, otherwise A will pass through. Why is this?

@softcorns Could you please describe your problem in more detail. It’s hard to understand the situation you are in. Maybe add a gif?


For your text, I understand in some cases only hits if goes fast?? Normally, it hapens the otherside. If speed is too high, it does not collide. To prevent this, you need to change the Collision detecting mode in the Rigidbody. Make it continous to allow really quick objects, detect all the colliders.