Foces only change during collision

I am trying to control a cube with the keyboard inputs. I want to change the acceleration of the cube while it is in the air, but the applied forces will only update during a collision or if I set the drag to a large value. I have included my code below.

 using UnityEngine;
 using System.Collections;
 
 public class CubeMove : MonoBehaviour {
     
     private Vector3 input;
     private float maxSpeed=5f;
     private float accelSpeed=500f;
     
     // Use this for initialization
     void Start () {
     
 
 
     }
         
         // Update is called once per frame
         void Update () {
             input=new Vector3(Input.GetAxisRaw("Horizontal"),0,
                 Input.GetAxisRaw ("Vertical"));
             
             if(rigidbody.velocity.magnitude<maxSpeed){
                 rigidbody.AddForce(input*accelSpeed,
                     ForceMode.Acceleration);
                 print(rigidbody.velocity);
             }
                 
         }
     }