Character doesn't fall back down when jumping

I am trying to get my character to jump, but when the character jumps, it moves up about 50px above the ground, and doesn't come back down, and I cannot figure out why this is happening. Here is the code that I am using on the character

 using UnityEngine;
 using System.Collections;

 public class Player : MonoBehaviour {

     public float jumpForce    = 100f;
     public float groundRadius = 0.2f;
     public Transform groundCheck;
     public LayerMask whatIsGround;

     protected bool jump       = false;
     public bool grounded      = false;

     void Update(){
         if(Input.GetButtonDown("Jump") && this.grounded){
             this.jump = true;
         }
     }

     void FixedUpdate(){
         this.grounded = Physics2D.OverlapCircle(this.groundCheck.position, this.groundRadius, this.whatIsGround);
         if(this.jump){
             rigidbody2D.AddForce(new Vector2(0f, this.jumpForce));
             this.jump = false;
         }
     }
 }

Here is the character's settings: