How does rigidbody works?

I have two block in my scene, block_A and block_B.
block_A has both the rigidbody(no gravity) and a box-collider while block_B only has the box-collider.
I add a SimpleMove script to the two blocks as below:

using UnityEngine;
using System.Collections;

public class SimpleMove : MonoBehaviour {
	public float speed = 10f;
	private Rigidbody body;
	// Use this for initialization
	void Start () {
		body = GetComponent<Rigidbody>();
	// Update is called once per frame
	void Update () {
		if (body != null){
			body.AddForce(speed * Time.deltaTime, 0, 0);
			transform.Translate(speed * Time.deltaTime, 0, 0);

I put the two blocks in a line , and set the speed fields of the script so that they could move forward to each other.

When the speed fields changes, the results are:

  1. block_A speed 0 block_B speed 10, block_B will cross block_A.
  2. block_A speed -0.1 block_B speed 10, block_B will push block_A to the left.
  3. block_A speed -0.1 block_B speed 100, block_B will cross block_A.

So I don’t understand these.Thanks if you can help me~!

Did you already watch the tutorial on Colliders and Rigidbodies?