# Realistic angular velocity for rolling sphere in Unity 5.1

I'm trying to make a small 2D game with a rolling ball/sphere using Unity 5.1, but if find the angular velocity of the ball weird.

On this first image (https://i.sstatic.net/O1Ksb.jpg), you can see the sphere in 2D and in its initial position. On this second image (https://i.sstatic.net/HLHHT.jpg), the sphere was moved by rolling until it made a 90° turn.

But the distance traveled by the sphere is greater than it should, if you wanted to be to be realistic : you can see that the radius of the circle is equal to the size of the squares' sides, so the circle circumference should be equal to ~6.28 (in square side size). If the sphere was traveling realistically, it should travel ~1.57 (in square side size) to turn 90°. But in the second image, we can see that it take 3 and not 1.57 .

The controller of the sphere is simply adding a force when a left or right button is pressed :

public class PlayerController : MonoBehaviour
{
public float speed;
private Rigidbody2D rg2d;

void Start()
{
rg2d = GetComponent<Rigidbody2D>();
}

void FixedUpdate()
{
float moveHorizontal = Input.GetAxisRaw("Horizontal");

Vector2 movement = new Vector2(moveHorizontal, 0.0f);
}
}


So my question is : how can I make the angular velocity realistic in this situation? Or am I doing something wrong?

Thanks for taking the time, I really appreciate !

• You should try to tweak two things in different combinations: 1) angular drag of Rigidbody2D; 2) friction of PhysicsMaterial2D. Second one may help. Commented Oct 20, 2015 at 6:02
• Angular drag doesn't do anything, but the friction added by the PhysicsMaterial2D seems to work. Thanks ! Commented Oct 22, 2015 at 13:29
• I'm gonna make this comment an answer. Commented Oct 23, 2015 at 5:43

This is because the sphere has a zero friction and simply slides along the surface. To correct the problem, add PhysicsMaterial2D to your sphere and set friction value greater than zero: