c# character falls slowly

i am trying to follow an fps tutorial but it is in js but i use c# the gravity is set to -9.87 and the character is only 2 units in height i can jump but it goes up a really small amount and then falls down really slowly here’s the script

using UnityEngine;
using System.Collections;

public class PlayerMovement : MonoBehaviour {
	public float walkAcceleration = 5;
	public mouseLook Script;
	public float maxWalkSpeed = 20;
	Vector2 horizontalMovement;
	public float jumpVelocity = 20;
	public bool grounded = false;
	public float maxSlope = 60;
	// Update is called once per frame
	void Update () {
		horizontalMovement = new Vector2(rigidbody.velocity.x, rigidbody.velocity.z);
		if(horizontalMovement.magnitude > maxWalkSpeed){
			horizontalMovement *= maxWalkSpeed;
		rigidbody.velocity = new Vector3(horizontalMovement.x, 0, horizontalMovement.y);
		transform.rotation = Quaternion.Euler(0, Script.currentyRotation, 0);
		rigidbody.AddRelativeForce(Input.GetAxis("Horizontal") * walkAcceleration, 0, Input.GetAxis("Vertical") * walkAcceleration);
		if(Input.GetButtonDown("Jump") && grounded){
			rigidbody.AddForce(0, jumpVelocity, 0);
	void OnCollisionStay (Collision collision){
		foreach(ContactPoint contact in collision.contacts){
			if(Vector3.Angle(contact.normal, Vector3.up) < maxSlope){
				grounded = true;

please help i am really confused

i ended up switching to a different script sure it is automatically top speed but it works