How to create inertia in my script in Unity3d?

Question

Unity

private void FixeUpdate()
    {
        Vector3 direction = Vector3.forward * Input.GetAxis("Vertical") + Vector3.right * Input.GetAxis("Horizontal");
        rb.velocity = new Vector3(direction .x * speed * 10 * Time.deltaTime, direction .y * speed * 10 * 
                          Time.deltaTime, direction .z * speed * 10 * Time.deltaTime);
    }

How can I create inertia using this code?

Answer 1

Inertia is the property of a body to remain in some reference frames in a state of rest or uniform rectilinear motion in the absence of external influences, and also to prevent a change in its speed in the presence of external forces due to its inertial mass. Wikipedia

Here also prevent change, instead of at once change.