How to know if I collided with a especific side of a GameObject

Sometimes we need to detect if a Gameobject collided with a especific side of another GameObject, or even a side of the Screen.

We can do that cheking the "Normal" of the collision´s angle.

if (collision.collider.name == "Wall") { // collided with screen top
    Vector2 normal = collision.contacts[0].normal;
    if (normal == Vector2.down)
    {
this.enabled = false;
    }
}