A recycling plant has chips of hight density poly(ethylene) (HDPE, d=0.92g.mL) used for plastic bottles and poly(vinylchloride) (PVC, d=1.406g/mL) used for plumbing and house siding. The chips of these two plastics were inadvertently mixed and it is your job to separate them. How would you do this?
This is quite easy, with their different densities, particularly with the HDPE having a density less than one, and the PVC having a density greater than one.
The density of water is 1 g/ml. Materials with a density less than this will float, materials with a density greater than this will sink.
.092g/ml<1g/ml, so the HDPE will float, if placed in a container of water. 1.406g/ml>1g/ml so the PVC will sink if placed in a container of water.
To sort these two plastics, find a container that can hold water, and add enough water that you can separate the floating HDPE from the PVC that sank.