Whenever I start the unity editor and play it in the Game windows, sometimes the object can jump higher sometimes it is just small jump. I didn't change any value in my script nor changed it in inspector window.

It usually happens when I restart the unity editor or having my computer shutdown / restart and reopening the project.

Here are the jump code

   void jump() {
        if (isInGround) {
            float currentJumpForce = jumpForce * Mathf.Abs(rigidBody.velocity.x) / 3.53f;
            rigidBody.AddForce(Vector2.up * currentJumpForce);
            animator.SetTrigger("isJump");
        }
    }

I place the code inside the FixedUpdate method, for what I have read the physics calculation should be inside FixedUpdate right?

private void FixedUpdate() {
    if (Input.GetKeyDown(KeyCode.UpArrow)) {
        jump();
    }
}

I have read many are having similar problem, but it really doesn't answer this question.

Whenever I start the unity editor and play it in the Game windows, sometimes the object can jump higher sometimes it is just small jump. I didn't change any value in my script nor changed it in inspector window.

It usually happens when I restart the unity editor or having my computer shutdown / restart and reopening the project.

Here are the jump code

void jump() {
     if (isInGround) {
         float currentJumpForce = jumpForce * Mathf.Abs(rigidBody.velocity.x) / 3.53f;
         rigidBody.AddForce(Vector2.up * currentJumpForce);
         animator.SetTrigger("isJump");
     }
}

I place the code inside the FixedUpdate method, for what I have read the physics calculation should be inside FixedUpdate right?

private void FixedUpdate() {
    if (Input.GetKeyDown(KeyCode.UpArrow)) {
        jump();
    }
}

I have read many are having similar problem, but it really doesn't answer this question.

UPDATE:

I forget to explain it in the question. The jumpForce is calculated based on the velocity of the gameObject has. I capped the velocity to certain speed based on this code

void accelerate() {
     if (rigidBody.velocity.x <= maxSpeed) {
         rigidBody.AddForce(Vector2.right * acceletateForce);
     }
}

where maxSpeed is a constant. I know this is probably not the accurate way to cap the velocity, or is it? Maybe this is where it gets messed up?

I just kinda assume the velocity is the capped from the camera movement and the 'display' or the movement of the screen. It seems the same to me.