Provide your students with a variety of known and unknown masses, let the students figure out how it works!

This is tested in a calibrated mill, containing four blades of known mass.

The bomb, with the known mass of the sample and oxygen, form a closed system - no gases escape during the reaction.

Ludford wrote 17 known masses, a greater number than any other English composer of the time.

The inner glass tube contains a known mass of solvent.

At this point the mass of the sample can be determined from the required amount of known mass.

Now, slowly move the lightest known mass until the pan lifts.

As previously undiscovered fragments are found, the "total known mass" could, in principle, rise.

In these cases, the "total known mass" of the meteorite is fixed at the time of the find, and cannot increase.

The total known mass is about 3 tonnes.