Персонаж не прыгает Unity

почему если пишу if, то rb.AddForce(Vector2.up * jumpForce, ForceMode2D.Impulse) перестает работать. Вот код:

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


public class controller : MonoBehaviour
{
    //private
    private float horizontal = 0f;
    private bool isGround = false;
    private float vertical = 0f;
    
    
    
    public Rigidbody2D rb;
    public float speed;
    public float jumpForce;
    
    void Start()
    {
        rb = GetComponent<Rigidbody2D>();
    }

    private void OnTriggerStay2D(Collider2D collision)
    {
        if(collision.tag == "ground") isGround = true;
    }

    private void OnTriggerExit2D(Collider2D collision)
    {
        if (collision.tag == "ground") isGround =false;
    }
    void Update()
    {
        horizontal = Input.GetAxis("Horizontal");
        rb.velocity = new Vector2(horizontal * speed, rb.velocity.y);


        
            if(isGround && Input.GetKeyDown(KeyCode.W)) {
            rb.AddForce(Vector2.up * jumpForce, ForceMode2D.Impulse);
        }
            
                
        
    }
}