TOP down 2d car physics

What I want to do is make a car game that is viewed from the TOP down, as in you see the roof of the car. My problem is that I can accelerate, and rotate the sprite, but I can't make it turn realistically like the car in the car demo that unity provides. I also have no idea how to do this, and I just started using unity's 2d mode. Any help is appreciated.

var power : float = 3; var maxspeed : float = 20; var turnpower : float = 2;

var curspeed : float;

function Update () { if(Input.GetKey(KeyCode.W)) { rigidbody2D.AddForce(transform.up * power); }

 if(Input.GetKey(KeyCode.S))
 {
     rigidbody2D.AddForce(-(transform.up) * power);
 }
 
 if(Input.GetKey(KeyCode.A))
 {
     transform.Rotate(Vector3.forward * turnpower);
 }
 
 if(Input.GetKey(KeyCode.D))
 {
     transform.Rotate(Vector3.forward * -turnpower);
 }

}

//function OnGUI() //{

//}