rg_ball.velocity += Time.deltaTime*k;

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

public class _switch : MonoBehaviour {

    public bool isReady = false;
    public float level=0;
    public bool drawText = false;
    
    void OnTriggerEnter(Collider other)
    {
  if(col.tag == "Player")
  {
   isReady = true;
   drawText = true;
  }
    }

    void OnTriggerExit(Collider other)
    {
  if(col.tag == "Player")
  {
   isReady = false;
   drawText = false;
  }
    }

    void Update()
    {
  if(Input.GetKeyDown(KeyCode.F) && isReady) SceneManager.LoadLevel(scene_1);
    }

    void OnGUI()
    {
  if(drawText) GUI.Label(new Rect(10, 10, 100, 25), "Press F to get"); //хз как правильно на java, написал на C#
    }
}