Density

mass - volume - density - relative density

What it shows:
The concept of mass per unit volume is punctuated by having several different substances on hand for comparison. In solid materials, we have equal size chunks ¹   of aluminum (2.7 gm/cc) and uranium (18.7 gm/cc) for comparison. For gases we typically use balloons filled with helium (0.18 gm/liter), air (1.29 gm/l), and sulfur hexafluoride (6.50 gm/l). Being 5 times heavier that air, the SF₆ balloon noticeably feels like it weighs more than the air filled one and drops like a rock (almost)! We all know what happens when you drop the He balloon; this can lead into a discussion of buoyancy. Rating *

1 They're cubes measuring 5 cm on a side. Most demonstration collections don't have chunks of uranium...ours has a story attached which can be found in the Uranium Block demo. Lead (11.4 gm/cc) or a bottle of mercury (13.5 gm/cc) could be substituted for the uranium.

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