Why is my player ball's movement bouncy and bumpy?

Question

I've come across an odd effect in Unity and would like to understand why it's happening. Using some simple code I've achieved a horizontal movement effect, of a ball across a flat square surface, yet the movement in any given direction is bumpy, as in, it's like the ball is bouncing slowly until it settles in a hole when the key is let up. I've never noticed anyone else's player object doing this, and there doesn't seem to be any instances of it out there, based on my research. One might describe it as "rolling through the inside of an egg carton". Does anyone knows why this is happening, if it's normal, or at the fault of my code?

Here's my code:

using System.Collections;
using System.Collections.Generic;
using UnityEngine;

public class Player : MonoBehaviour
{
    private Rigidbody rb;
    public float speed;

    //
    void Start()
    {
        rb = GetComponent<Rigidbody>();
    }
    //

    void FixedUpdate()
    {
        var gravity = new Vector3(Input.acceleration.x, Input.acceleration.z, Input.acceleration.y) * 9.8f;
        rb.AddForce(gravity * rb.mass, ForceMode.Acceleration);

        float horizontal = Input.GetAxis("Horizontal");
        float vertical = Input.GetAxis("Vertical");
        Vector3 movement = new Vector3(horizontal, 0.0f, vertical);
        rb.AddForce(movement * speed);
    }
}

And here's a GIF of what's happening:

Answer 1

I don't see any issues with your ball movement. The shadow is bumpy.

Shadow maps are textures with pixels, but smoothing is applied so that low resolution shadows don't appear pixelated. However, the shadows in the shadow map can still only move one pixel at a time. When the resolution is low, the pixels are large and the shadow motion will appear jumpy. Here's what it might look like without smoothing:

You can fix this by increasing the shadow resolution.

Answer 2

Fixed! The ball was rolling rather than gliding, and because it wasn't smooth enough, gave me the feeling it was bumpy.