You can do this without physics, as long as the ellipses don’t have to bounce off each other, just off walls…

Set an x and y value for the number of pixels the ellipse moves each time it draws, eg x=2, y=-3 (maybe use random numbers to set them), as well as a starting position

In draw, add x to the current x value and y to the current y value

Then check if x>WIDTH-EllipseDiameter/2 or x<EllipseDiameter/2. If so, you say x=-x, ie if you were adding pixels before each time, now you will subtracting them, so the ellipse reverses direction

Do the same for y, using HEIGHT instead of WIDTH

The reason for subtracting half the diameter of the ellipse above is that if the ellipse is centred at X,Y, then its left hand side is at X-EllipseDiameter/2, and you want to bounce when that edge reaches the left hand side.