Check if float is increasing/decreasing

Hello, I am in the process of recreating flappy bird, I am fairly new to C# and Unity. I am stuck at jumping, I want to create a float, which will be the bird’s altitude, then I want to check if the float is increasing/decreasing. If it is increasing or decreasing, then I want the state that to a boolean named isFlapping. Sorry, I don’t have any code that is worthy yet, therefore can’t show any code so far. Let’s take this code for an example:

using UnityEngine;
using System.Collections;

public class BirdPhysics : MonoBehaviour {

	public float jumpHeight = 8;
	public bool isFlapping = false;		//Check if bird is jumping
	
	void Start () {
		
	}

	void Jump(){
		rigidbody2D.AddForce(new Vector2(0f,jumpHeight));
	}

	void Update () {
		if(Input.GetKeyDown("up")){
			Jump ();
		}
	}
}

Given that you are using rigidbody2D, you can check the ‘y’ velocity:

In Update() or FixedUpdate(), you can do:

 isFlapping = (rigidbody2D.velocoty.y > 0.0);