Imagine you have four "see-through" boxes, all the same size,
and you fill each of them up with a different material.
Before you begin, try to guess which material has the least
mass and which has the most mass. (Mass is closely related to
weight. Here on earth, for all practical purposes, it's the
same thing.) Test your prediction by placing the materials two
at a time on this balance, and then placing them in their
correct slot below. (You'll know that you've actually placed
the material on the balance when you hear a clicking sound.)
Click on the "I'm done." button when you're finished.