Physics on a Ball

Hi, I have a ball that I want to properly display physics. What I mean by this is that I want to ball to roll properly from left to right, and then, if I change direction, I want the momentum to slow the ball down and accelerate from right to left. Additionally, when I jump, I don't want the ball to fall from left to right and right to left solely based on the user rocking the phone back and forth. Right now, I am having trouble with both the physics of movement and the physics of the ball in the air

My code for movement:

function Update () {
 var dir : Vector3 = Vector3.zero;
 dir.x = -Input.acceleration.y.5;
 transform.position.x += dir.x;
 //dir.y = -Input.acceleration.x.5;
 //transform.position.y += dir.y; }

var dir : Vector3 = Vector3.zero; var isFalling : boolean=true;

function Update () { var fingerCount = 0; for (var touch : Touch in Input.touches) { if (touch.phase != TouchPhase.Ended && touch.phase != TouchPhase.Canceled) fingerCount++; } if (fingerCount > 0) //&& !isFalling){ rigidbody.velocity.y=7; } isFalling=true; function OnCollisionStay(collisionInfo : Collision) { isFalling=false; }