why things sink when everything is floated? and do u think the liquid will seperated next class?

we do this on Thurday this experiment is so miraculous i did see this on before
is so cool.
why things sink when everything is floated?i think why something sink but something not . because i think everything density is different like wood .rock. metal .plastic.they weight is different
so something is haver.so will sink or floated.

and do u think the liquid will seperated next class? will i think is no because if the water and oil they are no to dissolve so water and oil is not together because the experiment show us the are separate because water and oil's density is different oil's density is small than water so the oil is upstar