C# - How change transform.translate of an gameObject by touching touchscreen!

I want change the speed of an gameObject by touching the touchscreen.
If a ball fall with this code, how can i do to change the speed of the ball for a period of time (1-2 sec)?

public float apeed = 1;

void Update(){
transform.Translate(0,-speed,0)
}

You need to modify the velocity of the rigidbody. If it happens once on touch, you can do it in Update. If it’s continuous, do it in FixedUpdate.