Unity : pool game emulator : The cue ball didn't bounce back as expected; instead, it continued to travel along the table's edge

The cue ball, after colliding with the table edge, didn't bounce back as expected; instead, it continued to travel along the table's rail, closely hugging its edge.

emulation

The following are the physical materials of the edge and the ball:

ball physical material

edge physical material

I have tried adjusting various coefficients, but it may either result in excessive elasticity or the ball still continuing to travel along the table's edge.

The following is the C# code which provide the velocity and direction of cue ball

using System.IO;
using UnityEngine;
using System.Collections;

public class CueBallController : MonoBehaviour
{
    private string cueball_position_Path = "D:/Unity Project/testtest/Assets/Resources/cueball_position.json";
    private string HitParams_Path = "D:/Unity Project/testtest/Assets/Resources/HitParams.json";

    [System.Serializable]
    public class HitParams
    {
        public float HitSpeed;
        public Vector3 HitDirection;
    }

    HitParams LasthitParams;

    private Rigidbody rb;

    public float stationaryThreshold = 0.01f;
    private bool allBallsStationary = false;

    // Start is called before the first frame update
    void Start()
    {
        LoadInitialPosition(cueball_position_Path);
        rb = GetComponent<Rigidbody>();
        LasthitParams = new HitParams();
    }

    // Update is called once per frame
    void Update()
    {
        allBallsStationary = CheckIfAllBallsAreStationary();

        if (allBallsStationary)
        {
            // Load initial parameters from JSON file
            HitParams newHitParams = LoadHitParams(HitParams_Path);

            if (newHitParams != null && (newHitParams.HitSpeed != LasthitParams.HitSpeed || newHitParams.HitDirection != LasthitParams.HitDirection))
            {
                // Normalize the initial direction and apply the initial speed
                Vector3 hitVelocity = newHitParams.HitDirection.normalized * newHitParams.HitSpeed;

                StartCoroutine(MoveWithDelay(2.0f, hitVelocity));

                LasthitParams = newHitParams;
            }
        }
    }

    private void LoadInitialPosition(string path)
    {
        if (File.Exists(path))
        {
            string json = File.ReadAllText(path);
            Vector3 position = JsonUtility.FromJson<Vector3>(json);
            transform.position = position;
        }
        else
        {
            Debug.LogError("JSON file not found at: " + path);
        }
    }

    private IEnumerator MoveWithDelay(float delay, Vector3 hitVelocity)
    {
        yield return new WaitForSeconds(delay);

        rb.velocity = hitVelocity;
    }

    private HitParams LoadHitParams(string path)
    {
        if (File.Exists(path))
        {
            string json = File.ReadAllText(path);
            HitParams loadedHitParams = JsonUtility.FromJson<HitParams>(json);
            return loadedHitParams;
        }
        else
        {
            Debug.LogError("JSON file not found at: " + path);
            return null;
        }
    }

    private bool CheckIfAllBallsAreStationary()
    {
        GameObject[] balls = GameObject.FindGameObjectsWithTag("Ball");
        float angularThreshold = 0.01f;

        foreach (GameObject ball in balls)
        {
            Rigidbody ballRigidbody = ball.GetComponent<Rigidbody>();

            if (ballRigidbody != null &&
                (ballRigidbody.velocity.magnitude > stationaryThreshold ||
                ballRigidbody.angularVelocity.magnitude > angularThreshold))
            {
                return false;
            }
        }

        if (!rb.IsSleeping()) return false;

        return true;
    }
}

This issue has to do with the default physics configuration. Low velocity impacts are treated as inelastic collisions and the bounce is ignored (even if you set it up in your physics material). This is done to help calm down the physics simulation when you have a pile of slow moving rigid bodies all colliding with each other.

For 3D physics you need to lower the Bounce Threshold under Edit->Project Settings->Physics

For 2D physcis you need to lower the velocityThreshold under Edit->Project Settings->Physics 2D

Don't make the value too low, something like 0.1 should be enough.