objects moving on there on :(

i created a simple motion script that takes 4 inputs.... up,down,left and right..
script is working right when there is only one rigid body(the sphere which i`m contrlling)
but when i create a second sphere, having a rigid body component but not the controlller script...
problem occurs..

they will move right for few inputs and after that .... they will start to move on there own ....
sometimes oppsite from each other

however the variables x and y i used in my script are still showing 0 in inspector tab

my script :

using UnityEngine;
using System.Collections;

public class NewBehaviourScript : MonoBehaviour {

public float x,y ;
// Use this for initialization
void Start () {
Debug.Log(" i am alive !");
}

void OnGUI ()
{
if (Input.GetKey ("up"))
{
y=0.05f; ;
}
else if (Input.GetKey ("down"))
{y=-0.05f;
}
else if (Input.GetKey ("left"))
{x=-0.05f;
}
else if (Input.GetKey ("right"))
{x=0.05f;
}

if(GUI.RepeatButton (new Rect(20,40,60,20), "-->"))
{
x=0.05f;
}

if(GUI.RepeatButton (new Rect(80,40,60,20), "<--"))
{
x=-0.05f;
}

if(GUI.RepeatButton (new Rect(40,20,80,20), "^"))
{
y=0.05f;
}

if(GUI.RepeatButton (new Rect(40,60,80,20), "V"))
{
y=-0.05f;
}
}

// Update is called once per frame
void Update ()
{
transform.position += Vector3.right * x;
transform.position += Vector3.forward * y;
y=x=0;
}
}

 

you're probably getting some sort of velocity/momentum build up from the physics engine "doing it's thing"... try setting the rigidbodies to kinematic

 

yooo!! ..... correct