unity example - ball jump

Ball.cs

using UnityEngine;

public class Ball : MonoBehaviour
{
    private Rigidbody rb;

    [Header("Jumping")]
    public Vector3 jumpForce = Vector3.up;

    public float jumpTimeout = 0.1f;
    private bool nextJump;
    private float nextJumpTime;

    [Space(20)]
    [Header("Grounded")]
    public LayerMask groundMask;

    public float groundCheckDistance = 0.1f;

    private bool isGrounded;

    private float halfHeight;
    private float groundCheckRadius;


    // Use this for initialization
    void Start()
    {
        rb = GetComponent<Rigidbody>();
        halfHeight = GetComponent<Renderer>().bounds.size.y / 2f;
        groundCheckRadius = GetComponent<Renderer>().bounds.size.x / 4f;
    }

    // Update is called once per frame
    void Update()
    {
        HandleInput();

        if (isGrounded && nextJump && nextJumpTime < Time.time)
        {
            Jump();
            nextJumpTime = Time.time + jumpTimeout;
        }
    }

    private void HandleInput()
    {
        if (Input.GetKeyDown(KeyCode.Space))
        {
            nextJump = true;
        }

        if (Input.GetKeyUp(KeyCode.Space))
        {
            nextJump = false;
        }
    }

    void Jump()
    {
        rb.AddForce(jumpForce, ForceMode.Impulse);
        rb.velocity = new Vector3(rb.velocity.x, 0, rb.velocity.z);
    }

    private void FixedUpdate()
    {
        CheckGround();
    }


    void CheckGround()
    {
        RaycastHit hit;
        isGrounded = Physics.SphereCast(transform.position, groundCheckRadius, Vector3.down, out hit, groundCheckDistance + halfHeight - groundCheckRadius, groundMask);
    }
}