Measuring the density of rocks and metals
The question
How does the density of an iron object compare with that of ordinary rocks, and could density identify a meteorite?
Iron meteorites have a density of about 7.5 to 8 g/cm³, stony meteorites about 3 to 3.7 g/cm³, and most Earth rocks about 2.5 to 3 g/cm³. Measuring density is a non-destructive test scientists use.
Equipment
- A digital scale reading to 0.1 g
- A measuring cylinder, or a jug and an overflow can
- Samples: granite, sandstone, basalt, chalk, a steel bolt and other objects
- A calculator
Method
- Weigh each sample in grams.
- Put water in the measuring cylinder and read the level. Lower the sample in on a thread and read the new level. The rise is the volume in cm³.
- Calculate density = mass ÷ volume.
- Repeat each measurement three times and take the mean.
- What to measure
- Mass (g), volume (cm³) and density (g/cm³) for each sample, with the spread of your repeats.
- How to present it
- A bar chart of densities, with bands marked for Earth rocks, stony meteorites and iron meteorites, and a discussion of how accurate your measurements were.
- Take it further
- Use the site's density calculator, which uses weighing in air and in water, and compare the two methods. Which gives the smaller uncertainty, and why?
Safety
Lower samples gently so the glass cylinder does not crack, and wipe up spills.