How to keep player momentum after jumping (2D)?

Question

I'm creating a Mario clone and I need to keep the player's forward momentum into the jump and then onward into the landing. I can't figure out how to achieve this. Every time I land, the player has to build up momentum again. Any Idea how to fix this? I've tried several solutions to no avail. I'm thinking it has something to do with how I'm adding force and acceleration to the player when holding left or right. Not sure though any help would be much appreciated. thanks in advance.

Here's my code:

Animator animator;
Rigidbody2D rb;
bool isGrounded;
public float moveSpeed;
public Vector2 acceleration;
public float jumpHeight;
public float lowjumpMultiplier;
public Transform groundCheckM;
public Transform groundCheckL;
public Transform groundCheckR;
public float storedValue;

void Start()
{
    animator = GetComponent<Animator>();
    rb = GetComponent<Rigidbody2D>();
    transform.eulerAngles = new Vector3(0, 0, 0);
}


private void Update()
{

   if
         ((Physics2D.Linecast(transform.position,groundCheckM.position, 1 << LayerMask.NameToLayer("Floor/Platforms"))) || //Check if grounded
         (Physics2D.Linecast(transform.position, groundCheckL.position, 1 << LayerMask.NameToLayer("Floor/Platforms"))) ||
         (Physics2D.Linecast(transform.position, groundCheckR.position, 1 << LayerMask.NameToLayer("Floor/Platforms"))))
    {
        isGrounded = true;
        animator.SetBool("Jump", false);
    }
       
   else
    {
        isGrounded = false;
    } 

    animator.SetFloat("Walk", rb.velocity.x);  //Set animation float to x velocity 
   
    if (rb.velocity.x <= 0.03f && rb.velocity.x >= -0.03f && isGrounded) //Play "Idle" animation 
    {
        animator.Play("Mario_Idle");
    }

    if (rb.velocity.x >=4 || rb.velocity.x <=-4)

    {
        animator.speed = Mathf.Abs(rb.velocity.x / 5.5f); //Increase speed of walking animation with player's walking speed 
    }

}
void FixedUpdate()
{

    if (Input.GetKey("d") || Input.GetKey("right")) //Move player to the right 
    {
        rb.AddForce(acceleration * rb.mass);
        transform.rotation = Quaternion.Euler (0, 0, 0);
    }

    else if (Input.GetKey("a") || Input.GetKey("left")) //Move player to the left
    {
        rb.AddForce(-acceleration * rb.mass);
        transform.rotation = Quaternion.Euler(0, 180, 0);
    }

        if (rb.velocity.x >= 10)
        {
            rb.velocity = new Vector2(10, rb.velocity.y);   //Cap player speed at 10 when moving right
        }

    else if (rb.velocity.x <= -10)
        {
            rb.velocity = new Vector2(-10, rb.velocity.y);  //Cap player speed at 10 when moving left 
    }


    if (Input.GetKey("space") && isGrounded) //Player jump 
    {
        rb.velocity += new Vector2(rb.velocity.x, jumpHeight);
        animator.SetBool("Jump", true);
    }

}

}

Answer 1

If you want to keep your momentum when jumping, you could store it in a variable that will increase until it reaches the max, or you let go of the key.

float acceleration;
float accelFactor = 0.6f;
float deAccelFactor = 1f;

bool jumping; //you should set it to true when jumping and false, when not.
Rigidbody2D rb;

void Start(){
    rb = GetComponent<Rigidbody2D>();
}
void Update(){
    if (Input.GetKeyDown(KeyCode.D))
    {
        Accelerate();
        rb.AddForce(acceleration * rb.Mass);
    }
    else if (jumping)
    {
        rb.AddForce(acceleration * rb.Mass);
    }
    else
    {
        DeAccel();
    }
}
void Accelerate(){
    acceleration += accelFactor * Time.deltaTime;
    acceleration = Mathf.Clamp(acceleration, 0, maxAccel);
}
void DeAccel(){
    acceleration -= deAccelFactor * Time.deltaTime;
    acceleration = Mathf.Clamp(acceleration, 0, maxAccel);
}

This is what I would recommend using, that is, if I understand what you mean.

Answer 2

I feel dumb but the answer was in the physics material. Once I lowered the friction, it allowed momentum from the jump to carry into the player's run speed. I guess it's a good reminder to tinker directly inside Unity and its built in physics system.