doesnt detect collision ?

im trying to make a character jump, so to make that i was taught in college to detect a collision with the floor, which is in another layer (character is in layer 8, and the platforms are in layer 9) here's the whole thing, sorry for the spanish, here are some translations saltar= jump velocidad=velocity fuerzasalto= jumping force puedosaltar= icanjump mover=move

     public float velocidad;
     public SpriteRenderer renderizador;
     public float fuerzaSalto;
     public Rigidbody2D rb;
     public bool puedoSaltar;
 
 
     // Use this for initialization
     void Start ()
     {
         renderizador = GetComponent<SpriteRenderer>();
         rb = GetComponent<Rigidbody2D>();
 
     }
 
     // Update is called once per frame
     void Update()
     {
         Mover();
         Saltar();
        
     }
 
 
 
     public void Saltar()
     {
         if (Input.GetKeyDown(KeyCode.Space) && puedoSaltar == true)
         {
             rb.velocity = Vector3.zero;
             rb.AddForce(Vector3.up * fuerzaSalto, ForceMode2D.Impulse);
             puedoSaltar = false;
         }
     }
 
 
 
 
     public void OnCollisionEnter2D(Collision2D info)
     {
         if (info.gameObject.layer == 9)
         {
             puedoSaltar = true;
         }
     }
 
 
 
     public void Mover ()
     {
         if (Input.GetKey(KeyCode.RightArrow))
         {
             transform.position += Vector3.right * velocidad * Time.deltaTime;
             renderizador.flipX = true;
 
         }
 
         if (Input.GetKey(KeyCode.LeftArrow))
         {
             transform.position += Vector3.left * velocidad * Time.deltaTime;
             renderizador.flipX = false;
 
         }
     }
 
 
 }

thanks to everyone who took the time to read through this!