I have the classic balls that move in a line:

2. 
   
3. class Circle{
4.   float x,y,vx,vy,size;        
5. 
   
6.  Circle(float ax,float ay){
7.    x = ax;
8.    y = ay;
9.    size = 5;
10.    vx = random(-.1,.1);
11.    vy = random(-.1,.1);
12. }
13. 
    
14. void update(int w,int h){
15.    x += vx;
16.    y += vy;
17.    if(x < 0 || x > w) vx *= -1;
18.    if(y < 0 || y > h) vy *= -1;
19.  }
20. 
    
21. void draw(){
22.   pushStyle();
23.   noStroke();
24.   fill(0);
25.   ellipse(x,y,size,size);
26.   popStyle();
27. }
28. 
    
29. }

However, i don't want them moving in a line.

I want them moving in unregular curves. What can i add? noise? sin? cos?

Many thanks.