Density
Publication information:
Abstract
Aluminum/Uranium and SF6/Air/Helium density comparisons.
What It Shows
The concept of mass per unit volume, aka density, is shown by having several different substances on hand for comparison. In solid materials, we have equal size chunks1 of aluminum (2.7 g/mL) and uranium (18.7 g/mL) for comparison. For gases, we typically use balloons filled with helium (0.18 g/L), air (1.29 g/L), and sulfur hexafluoride (6.50 g/L). Being 5 times heavier that air, the SF6 balloon noticeably feels like it weighs more than the air-filled one and drops (almost) like a rock! We all know what happens when you drop the helium balloon; this can lead into a discussion of buoyancy.
Safety: Make sure that gloves are used to handle the uranium.
1 They are cubes measuring 5 cm on a side. Most demonstration collections do not have chunks of uranium. Ours has a story attached which can be found in the Uranium Block demo under Quantum Physics and Relativity, Radiation and Radioactive Decay. Lead (11.4 g/mL) or a bottle of mercury (13.5 g/mL) could be substituted for the uranium. For uranium and lead, make sure gloves are worn while handling. A less toxic, but also less dramatic option would be comparing a block of copper to the block of aluminum.
Full text
Aluminum/Uranium and SF6/Air/Helium density comparisons.
What It Shows
The concept of mass per unit volume, aka density, is shown by having several different substances on hand for comparison. In solid materials, we have equal size chunks1 of aluminum (2.7 g/mL) and uranium (18.7 g/mL) for comparison. For gases, we typically use balloons filled with helium (0.18 g/L), air (1.29 g/L), and sulfur hexafluoride (6.50 g/L). Being 5 times heavier that air, the SF6 balloon noticeably feels like it weighs more than the air-filled one and drops (almost) like a rock! We all know what happens when you drop the helium balloon; this can lead into a discussion of buoyancy.
Safety: Make sure that gloves are used to handle the uranium.
1 They are cubes measuring 5 cm on a side. Most demonstration collections do not have chunks of uranium. Ours has a story attached which can be found in the Uranium Block demo under Quantum Physics and Relativity, Radiation and Radioactive Decay. Lead (11.4 g/mL) or a bottle of mercury (13.5 g/mL) could be substituted for the uranium. For uranium and lead, make sure gloves are worn while handling. A less toxic, but also less dramatic option would be comparing a block of copper to the block of aluminum.