Chladni Plates are metal plates that cam be made to resonate when a bow is drawn across. Node lines become visible if salt or a light sand is dusted across the top. Chladni plates can resonate in a f(x,y) = sin(x)+sin(y) pattern. Red lines show some possible node lines that form if the middle is damped. Higher frequencies are denoted by larger squares, or more complicated node line pattern made by the salt.