BCE0020: An instance of type 'UnityEngine.Rigidbody' is required to access non static member 'AddForce': I don't understand the problem

Hello, I need help with this script because i don’t understand the problem:
unction Update ()
{
InputPC();
}

//------

function InputPC()
{
      //on va mettre les controles droites et gauches en bloquant le fait de faire les deux en meme temps
            if (Input.GetKey("left"))
            {
                 //on ajoute une force au rigi vers la gauche qui sera indépendante de la balle
                 rigidbody.AddForce(-Vector3.right);
      }
      else if (Input.GetKey("right"))     
      {
                 //la meme chose à droite
                 rigidbody.AddForce(Vector3.right);
      }
      
      //la meme chose mais pour sauter et descendre
      if (Input.GetKey("up"))
      {
                rigidbody.AddForce(Vector3.forward);
      }
      else if (Input.GetKey("down"))
      {
             Rigidbody.AddForce(-Vector3.forward);
      }
}

In line 24, you need a lower case ‘r’:

rigidbody.AddForce(-Vector3.forward); 

Upper case ‘R’ refers to the class, lower case refers to the instance.