The Chladni exhibit provides a means to visualize the normal modes of vibration of an object, usually a flat metal plate. This technique was devised by Ernst Chladni around the year 1787. The plate being studied is mounted horizontally and sprinkled on top with a very small amount of fine sand. It is attached at its center (or more accurately at its center of mass) to the top of a vertical post. The bottom of the post is attached to the center of a loudspeaker cone which forces it to vibrate up and down in a sine wave motion with an adjustable frequency. When the frequency is sufficiently close to one of the normal mode frequencies, the plate is excited into a 2-dimensional standing wave vibration. The driving oscillator is then said to be "in resonance" with that mode. During each cycle of the vibration, the plate bends and deforms slightly, such that some regions of the plate will be moving upwards while adjacent regions are moving downwards. Half a cycle later this situation will be exactly reversed. The boundaries between these regions of opposite vibrations are called nodal lines; there is no motion there. The nodal lines form a pattern that characterizes this particular normal mode. When the vibrations are sufficiently strong, they cause the grains of sand to dance or bounce off of the surface slightly and move towards the nodal lines where they come to rest, making the lines visible.

When searching for a mode, one slowly tunes the oscillator and looks for the dancing sand. The plates have many modes that can be excited in this way. The display reads the frequency in cycles per second or Hertz. Two of the higher modes for the square plate are shown in the photo, one at 1152 Hz and one at 1270 Hz. The lowest frequency mode for a particular plate might be called the "fundamental," which is around 70 Hz for the square plate. However, the frequencies of the higher modes are generally not harmonics or multiples of the fundamental. This is different from, for example, stringed instruments, where all of the higher modes are harmonics. Stringed instruments exhibit 1D standing waves while the plates exhibit 2D standing waves. Plucking a guitar string will excite the fundamental and the harmonic modes simultaneously, and they sound good together because the frequencies are all multiples of the fundamental. Chladni modes with higher frequencies typically have more complex nodal patterns and the regions between the nodal lines become smaller. In theory, there are an infinite number of such modes, but in practice only some of the lower order modes can be excited and visualized. For symmetric plates, such as the square plate, many of the nodal patterns exhibit a symmetrical character.

Note that the location of the central post is never on a nodal line. This location on the plate cannot at be at rest since the vibrating post is forcing it to move. It is often an anti-node, or point of maximal motion. Normal modes for which the center of mass is on a nodal line may exist, but cannot be excited by this method. There is an alternate method (not used here) for exciting a Chladni plate, in which the attachment post is fixed and does not vibrate. In this case the plate is usually excited by bowing at some point along the edge with a violin bow or something similar. This is the method that was used by Chladni and the only one possible at that time, since loudspeakers and other electronic components did not exist in 1787. This method can only excite modes where the attachment point is on a nodal line since now that point is fixed. Excitation of a particular mode may sometimes be achieved by touching the plate at one or more points that are on the nodal lines for that mode (see drawing.) Striking the plate with a xylophone mallet would be an alternate method to excite one or more modes. In an actual xylophone, the bars are in fact supported at 2 points on nodal lines for the fundamental mode of vibration.