How can meteorites be used to teach density?
Pupils measure the mass and volume of meteorites and ordinary rocks and calculate density, discovering that iron meteorites are about three times denser than common rocks.
Density is often taught abstractly, but meteorites give it a real purpose: density is one of the first clues that a rock might be from space.
Measuring mass. Use a digital balance reading to 0.1 gram.
Measuring volume. For irregular objects, use displacement. Part-fill a measuring cylinder with water, read the level, lower the specimen in on a thread and read again. The difference is the volume in cubic centimetres. For small samples, a eureka can and a small measuring cylinder also work. Real meteorites, especially irons, should be dried thoroughly at once; for this reason many teachers use replicas, or meteorites sealed in acrylic, which require measuring the block and subtracting a known value. Another option is to compare hand-held weight qualitatively.
Calculating. Density equals mass divided by volume. Typical results: iron meteorites about 7.5 to 8.0 grams per cubic centimetre; ordinary chondrites about 3.2 to 3.7; carbonaceous chondrites about 2.0 to 3.0; granite about 2.6 to 2.7; basalt about 2.9 to 3.0; pumice below 1.
Discussion. Why are iron meteorites so dense? They are mostly metal, which packs heavy atoms closely. Why might a meteorite be lighter than expected? Some are porous or contain water-bearing clays. Why is density only a clue, not proof? Some Earth rocks, such as haematite and magnetite ores and slag, are also dense.
Extension: pupils can predict the density of a mixture, such as a stony-iron pallasite, from its proportions of metal and olivine.