LEARN ABOUT DENSITY -- A PHYSICAL PROPERTY THAT IS UNIQUE TO EACH SUBSTANCE:

Density Flash Cards: Try your luck with these practice flash cards.
Density Review Game-- Challenge Level -- Shoot the Hoops with these more difficult questions... (FYI, if it asks you to sign in with an email address, you can just ignore that & click to play the review game.)
Online Density Simulation... click (near the edge) on the picture below to experiment with floating & sinking