Inconsistent jump height

I was testing jump heights for a 3D platformer game I'm making with double jump and found that the height the player achieves doing a grounded jump was slightly different than jumping in mid-air. More specifically, I considered the following player logic attached to a capsule with standard size on a cube at (0, 0, 0).

Code (CSharp):

1.  
2. using System.Collections;
3. using System.Collections.Generic;
4. using UnityEngine;
5.  
6. public class player : MonoBehaviour
7. {
8.     private Rigidbody rb;
9.     public float maxHeight;
10.     // Start is called before the first frame update
11.     void Start()
12.     {
13.        rb = GetComponent<Rigidbody>();
14.     }
15.  
16.     // Update is called once per frame
17.     void Update()
18.     {
19.         if(Input.GetKeyDown(KeyCode.Space)) rb.AddForce(Vector3.up*(5-rb.velocity.y), ForceMode.Impulse);
20.     }
21.     void FixedUpdate() {
22.         maxHeight = Mathf.Max(maxHeight, transform.position.y);
23.  
24.         rb.AddForce(Vector3.down*5, ForceMode.Acceleration);
25.     }
26. }
27.  

I tracked the max height for each jump and found that the player jumped 2 units for the first jump, but the second jump was around 2.4 units, even though I am adding almost the same force with each jump. How can I make the jump heights of the two jumps exactly the same? Is this a quirk with the physics system?

 

You are adding force by doing:

Code (CSharp):

1. Vector3.up * (5 - rb.velocity.y)

When doing that the second jump will be smaller if the player still goes upwards, and bigger if is falling.
Instead you should do:

Code (CSharp):

1. Vector3.up * 5

But this will make the jump still inconsistent, so you also have to do:

Code (CSharp):

1. rb.velocity = new Vector3(rb.velocity.x, 0, rb.velocity.z

This will reset the y velocity of the rigidbody.
Also, that code allows you to make infinite jumps