Editing Measurement (section)

=== Mass ===
{{Main|Weighing scale}}

''Mass'' refers to the intrinsic property of all material objects to resist changes in their momentum.  ''Weight'', on the other hand, refers to the downward force produced when a mass is in a gravitational field. In [[free fall]] (no net gravitational forces) objects lack weight but retain their mass. The Imperial units of mass include the [[ounce]], [[pound (mass)|pound]], and [[ton]]. The metric units [[gram]] and kilogram are units of mass.

One device for measuring weight or mass is called a weighing scale or, often, simply a "scale". A spring scale measures force but not mass, a balance compares weight; both require a gravitational field to operate. Some of the most accurate instruments for measuring weight or mass are based on load cells with a digital read-out, but require a gravitational field to function and would not work in free fall.