The applet desing by prof Hwang, modified layout by Ahmed.
Original applet can find at [url=http://www.phy.ntnu.edu.tw/ntnujava/index.php?topic=2058.0]Did you see bended lines (red/green/blue squares)?[/url]
You can change the size of the circle with slider.
Try to un-check the show checkbox and see the difference feeling!