Vibrations on two dimensional surfaces are composed of fundamental modes which are characterized by two "quantum numbers" which define their shapes. For a circular drumskin, there are two types of node: circular and transverse. (There will always be one circular node at the edge of the drum.)
Use the buttons to the right to view different fundamental modes. Each button is labelled with the two quantum numbers defining a mode. (Please be patient while the animations are downloaded.)
When you think you have worked out the relationship of the quantum numbers to the simulations, you can test yourself by clicking on the button marked "random". When you believe you have identified the vibration, click in the box to the right of the "Random" button, type in the two quantum numbers separated by a comma (as they appear on the other buttons) and press "Enter". You will see a message indicating whether or not you are correct.