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.