Hawai'i Space Grant Consortium, Hawai'i Institute of Geophysics and Planetology, University of Hawai'i, 1996

Teacher Page

To understand the compactness of planetary matter by measuring mass and volume and relating these to density.


Density is defined as the average mass per unit volume; it is a measure of how much matter is squeezed into a given space. The more closely packed the molecules, the higher the density of the materials. In general, planetary bodies in our Solar System are composed of iron, rock, ice, liquids, gases, and in the special case of Earth, organics. This activity focuses on techniques to determine densities of cubes, spheres, or rods of metal, rock, and ice.

The equation for density is:

This Activity

Students will practice finding densities of regular and irregular objects. We define regular objects as having lengths, widths, heights, or diameters that can be easily measured and used to calculate volume. Irregular objects, then, cannot be so easily measured. Their volumes are determined by water displacement techniques.


Review and prepare materials listed on the student sheet. Collect steel ball bearings or rods, rocks, and ice cubes.

In Class

Each team of students should have the experience of determining the volume of regular and irregular objects. Remind them that 1 milliliter is equal to 1 cubic centimeter volume.


Fun fact: Saturn is less dense than water! Saturn would float if you could find a bathtub large enough to hold it!

Go to Density Student pages.

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