# What Is Mass Measurement?

All of the things we use, from our smartphones to the food on our plates, have mass. But what exactly is mass?

Mass measurement is crucial to many scientific disciplines. Accurate measurements help us make more accurate predictions and discoveries.

The SI unit of mass is the kilogram, defined by the international prototype of the kilogram (a platinum-iridium cylinder stored at the International Bureau of Weights and Measurements). Other units of mass are based on fundamental constants.

## Definition

Mass is an intrinsic property of matter that determines its resistance to change when a force is applied. It also determines the strength of its gravitational attraction with other bodies.

The SI unit of mass is the kilogram (kg). This is a physical prototype, stored in a vault in France. It is used in calibration of other mass standards to ensure they have the correct labeled mass.

Unlike weight, which is dependent on gravity, mass does not change with position or the arrangement of the matter within the object. If you were to move from the Earth to Mars, your weight would decrease but your mass wouldn’t. The more matter something has, the more it will weigh, but this is not always the case since the size of an object doesn’t necessarily imply the amount of matter inside. Mass can be measured in a variety of ways, including direct and indirect weighings, measuring the acceleration due to gravity, and measuring atomic particles.

## Measurement

In everyday use, the words “mass” and “weight” are often used interchangeably to describe heaviness. However, mass is the amount of matter in an object or substance and depends on what type of atoms it is made of and how many of them there are.

In the metric system, mass is measured in kilograms (kg) or grams, and is a scalar quantity. It is different from weight, which is a vector quantity that has magnitude and is directed toward the center of Earth or other gravity well. Weight is usually measured using a spring balance.

Passive gravitational mass is a measurement of the strength of an object’s interaction with a gravity field. It is calculated by dividing the object’s weight by its acceleration when free-falling. This is useful for comparing objects in space and other places with no gravity. To make it easier to compare smaller quantities, scientists developed the dalton, which is defined as one twelfth of the mass of a carbon-12 atom.

## Applications

Mass metrology can provide a number of critical benefits to your research and production processes. In disciplines that require conversion of an object’s mass to its weight (such as structural engineering), accurate measurement allows you to determine the load on a structure due to gravity.

In chemical synthesis, precise mass measurement allows you to monitor the formation of chemically sensitive layers. For this, you can use gas sensors to detect changes in a sample’s surface that correlate with its changing mass.

A newer approach is to measure the actual molecular mass of a sample using mass photometry. This technique uses light scattering from individual molecules in contact with the measurement surface to generate a signal that directly correlates with its mass. This enables the measurement of mass of biomolecules at a single molecule level, revealing important biological information such as protein subpopulations and molecular heterogeneity that are hidden from techniques that only measure bulk sample properties.

## Terminology

Although the terms weight and mass are sometimes used interchangeably, the two are distinct physical properties. While mass measures an inertial property of matter, weight is the force exerted on a body by gravity.

If no systematic errors exist in a sample of measured masses, their mean value will get closer to the calculated exact mass as the number of measurements increases due to (partial) cancellation of positive and negative deviations. In such a case, the average experimental mass error, defined as x or Dmi, will also reduce.

However, it should be noted that x is not an indication of the precision, which is better expressed as the standard deviation of the sample mass error distribution, s = Dmi2n-1. This value is often quoted as the root mean square error, or RMS error. Using these terms in a statistical context can be confusing and misleading.

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