Explain a sand pendulum in a few p a r agraphs

also, answer this please:

Identify a periodic phenomenon in nature (ie phases of the moon, rising and falling of tides) and c reate a graph clearly showing the cyclic nature of the process. Clearly label the axes of your graph and identify the amplitude, frequency, period and wavelength of the phenomenon. There should be numerical values for significant quantities such as crests and troughs. Include a paragraph describing the entire process through at least one cycle.

Reference: Phsics I just need this to get done please help.