How can i make it so that the object doesnt instantly go to top speed. Here is my code

Questions & Answers
1

using System.Collections;
using System.Collections.Generic;
using UnityEngine;

public class liikkuu : MonoBehaviour
{
Rigidbody m_Rigidbody;
float m_Speed;

void Start()
{
    //Fetch the Rigidbody component you attach from your GameObject
    m_Rigidbody = GetComponent<Rigidbody>();
    //Set the speed of the GameObject
    m_Speed = 30.0f;
}

void Update()
{
    if (Input.GetKey(KeyCode.W))
    {
        //Move the Rigidbody forwards constantly at speed you define (the blue arrow axis in Scene view)
        m_Rigidbody.velocity = transform.forward * m_Speed;
    }

    if (Input.GetKey(KeyCode.D))
    {

        transform.Rotate(0, 1f, 0);
    }

    if (Input.GetKey(KeyCode.A))
    {

        transform.Rotate(0, -1f, 0);
    }

}

}

2

The problem is with this line:

 m_Rigidbody.velocity = transform.forward * m_Speed;

if you want to gradually accelerate to top speed, you should do something like this:

 public float MinSpeed =  your minimum speed ;
 public float MaxSpeed = m_Speed;
 public float accelerationSpeed;
 float CurrentSpeed;
 
  void Update()
  {   
     if (Input.GetKeyDown(KeyCode.W))  // on key W down set current speed to minimum speed
     {
         CurrentSpeed = MinSpeed;
     }

     if (Input.GetKey(KeyCode.W)) // accelerate while holding the key
     {
         CurrentSpeed += accelerationSpeed;
         m_Rigidbody.velocity = transform.forward * CurrentSpeed ;
     }

     if (Input.GetKeyUp(KeyCode.W))  // on key W up reset current speed to minimum speed
     {
         CurrentSpeed = MinSpeed;
     }
  }