Free fall or Jump without AddForce

Hello, I asked this question before, but it wasn't answered and became "Forgotten in the Abyss". The problem is with the ball acceleration when it jumps, it gains speed from nowhere for no reason.
However, I did a research and found out what the problem might be. Long story short I'm now looking for a way to cancel the AddForce function that rolls my ball on the ground, when the ball jumps. Basically I want to simulate the real world physic, it's when you jump, the force only applied at the moment when you literally blast off the ground, it's then "fades out" and no force at all at the top height of your jump, it's where the gravity fully enters the scene.

     var moveHorizontal : float = Input.GetAxis ("Horizontal");
     var moveVertical : float = Input.GetAxis ("Vertical");
     var movement = Vector3(moveHorizontal, 0.0f, moveVertical);
     rigidbody.AddForce(movement * rotationSpeed * Time.deltaTime);
     // jumping
     if (Input.GetKeyDown(KeyCode.Space) && IsGrounded())
     {
         rigidbody.velocity = Vector3(rigidbody.velocity.x, jumpHeight, rigidbody.velocity.z);    
     }

IsGrounded() detects whether the ball is on the ground (via RayCast), I tried to set AddForce to "if (IsGrounded() == true)", but in this case the ball doesn't roll at all. I also tried to set rigidbody.velocity.x to Vector3.zero when ball reaches the top height, but in this case it falls down immediately (also, finding top height is fairly difficult because I have ground lifted on various levels on the scene and height detection is not ground relative). Loops don't work either way. Any advice, please?