Getting kids to understand the difference between weight and mass is essential for maths and physics. Learning early will make it easier for them to grasp these concepts when they’re older.
The modern metric system relies on immutable natural phenomena to define its base units, which can be multiplied or divided to generate other units like the liter for volume. The international prototype kilogram is a solid cylinder kept at NIST.
History
There are a wide variety of measurement systems that have been used throughout history. These vary from highly localised units to a standard international system known as the Systeme International d’Unites (SI).
These varied systems were typically based on visual or physical observation with a range of tools – such as sundials and stone cubes – for comparing measurements. These were supplemented by the invention of scales and more accurate weighing instruments.
In 1875 the seminal Treaty of the Metre led to the fashioning and distribution of artefacts that defined the metre and kilogram. These formed the basis for a coherent set of SI base units and the governing body that oversees them, the Conference Generale des poids et Mesures or CGPM. For historical reasons, the kilogram is the only one of the seven SI base measurement units whose name and symbol, g, include a prefix to distinguish it from decimal multiples of 1000 or 103.
Measurement techniques
From measuring the height of a future-building to assessing the quality of a new machine, measurement techniques lay the groundwork for every major engineering feat. They fall into two categories: quantitative and qualitative. Quantitative measures are numbers-based, while qualitative measures focus on evaluating properties and attributes that cannot be expressed as numbers.
The most common measure used in the field of engineering is weighing. Weighing instruments work by comparing the object being measured to a set of stainless steel weights that are calibrated against conventional mass. This allows scientists to determine the object’s conventional mass, or true weight minus the effects of buoyancy.
Other types of measurements are more complex, involving micro-electro-mechanical systems like accelerometers, which are found in everything from car safety devices to inkjet printer nozzles. These systems can help engineers constrain errors and ensure precision when working with a wide range of variables, from temperature to vibration. Other types of advanced measurement technologies include 3D laser scanners that can capture the dimensions and shape of an object or environment with incredible accuracy.
Common misconceptions
Students often have difficulty with the idea that mass can change based on the gravitational force. For example, if you have 40 kg on Earth, your weight would be less on the Moon or in space, but your mass remains the same.
It is also a common misconception that weight and matter are the same thing. In fact, matter is made of many different things, including atoms and molecules. The density of a substance is determined by its atoms, while the weight of an object is created by its gravitational pull.
The unit kilogram is an important part of the metric system, but many people have trouble understanding how it works. The key to reducing the confusion is to use hands on resources, and to encourage the students to use the units in contexts other than measuring lengths. For example, they may find it easier to understand that if an object doubles in size, its csa and volume will also double, but not its weight.
Future developments
In science, mass plays a critical role in everything from atomic weights to molecular structures. In technology, it is an essential consideration in a wide variety of industries including food production, pharmaceuticals, construction, automotive, chemical, and aerospace manufacturing.
Precision mass measurements are also fundamental to advanced technologies such as atom-beam and laser spectroscopy. These advances in physics have revolutionized analytical chemistry and helped to solve some of the most challenging problems in modern physics.
In the future, NIST hopes to streamline its current calibration chain and bring cutting-edge mass measurement capabilities to industrial and scientific customers by developing a new tabletop Kibble balance procedure. This would eliminate the need to send the national prototype kilograms back and forth between NIST and its international partners for yearly recalibration. Instead, the Kibble balance could be used to directly calibrate a customer’s mass standards, based on the air density established by NIST at the time of the calibration and at the time of use.