Unity3d Billiard/Pool aiming issue

Question

I'm trying to calculate what angle to hit a pool ball and predict where ball will go to.. I thought target ball should move within a normal direction.. but it moves on totally different direction

RaycastHit2D hit = Physics2D.CircleCast(cue.position, _radius, dir, 100f, ~(ignoreLayer));
if (hit.collider != null)
{
    Debug.DrawRay(hit.collider.transform.position, -1f * hit.normal, 
    Color.green, Time.fixedDeltaTime);
}

Here is result:

Set velocity

rb.velocity = dir * force;

Result:

How to find exact move direction, Thanks

Edit:

I have tried Double Radius Casting this works only half way.. only when ray inside inner circle

Answer 1

I suppose this is just a limitation of the physics engine, which is optimized for speed and use in games, and is not so exact.

Trying this myself in a simple 2D scene, I found that if I set the friction to 0.01 and the bounciness to 1.0, it works the way I would expect. (in Unity 2020.1)

In the small sample scene I added, there is a ball aiming at another so that the resulting angle should be 45 degrees. And after setting the phyics-mat to the properties with friction 0.01 and bounciness 1.0, the resulting angle is as expected.

With the default-mat I get the same behaviour you described.

Did you forget to assign the physics materials?

Have you single-stepped to the point of contact and checked if the aiming is correct?

my sample project trying this