# Mass Measurement Mass is a measure of how much matter something contains. It is not affected by shape or location. For example, your weight would be different if you were on the moon or at home, but your mass is the same.

The measurement of mass can be done by using a balance or through a novel bioanalytical technology called mass photometry (Young, et al. 2018).

## Units of Mass

Until recently, the amount of matter in an object was called its weight. But today, scientists use a different unit of measurement to describe the force of gravity on an object—its mass.

The SI unit for mass is the gram, or g. It is one-tenth of a cubic centimeter (cm3). For heavier objects, kilograms are used. One kilogram is equal to about 2.2 pounds.

Students might have a hard time understanding the concept of mass and how it relates to weight. To help them, you can provide examples of common everyday items like paper clips and pens that have similar shapes and sizes but differ in mass. Acquainting them with these units in their daily context will help them remember them more effectively.

It’s also important to point out that a gram is not the same as a pound. The pound is a measure of force, while the gram is a measure of matter. This is important to keep in mind because students will encounter both the pound and the gram in their future careers.

## Gravitational Forces

All things that have mass exert a force of attraction on everything else with mass, known as gravitational force. The strength of this force increases with the masses of the objects and decreases with the distance between them.

Newton’s universal law states that the force of gravitation between any two bodies is directly proportional to the product of their masses and inversely proportional to the square of the distance between them. Modern weighing practice is designed to take advantage of these proportions and thereby compare the masses of different weights.

In order to achieve the high level of accuracy needed in mass comparisons, it is necessary to correct for the gravitational configuration effect. This is caused by differences in the heights of the centers of gravity (of nominally equal weights) above their bases. These variations are caused by the size and shape of the weights and may result in systematic errors if they are not corrected.

## Measurement Instruments

The instruments used to measure mass are called balances.  A balance consists of two pans suspended from a pivot, with the unknown mass placed in one of them and standard masses added to the other until the beam is in equilibrium.

Laboratory balances are highly precise and capable of measuring mass to a fraction of a gram. These instruments are sensitive to air movement, so they must be kept in a stable environment with no drafts or vibrations.

The terms accuracy and precision are often confused, but they are distinct concepts. Accuracy is the degree to which a measurement agrees with the expected value. Precision is the consistency of measurements over time and between different instruments. Usually, recalibration improves an instrument’s accuracy, but does not necessarily improve its precision. Measuring tools include calipers to take dimensions of an object, rulers, and a variety of scales, including metric and decimal-point scales. They can also include thermometers, stopwatches, bubble inclinometers, protractors, and digital angle gauges.

## Errors in Mass Measurements

The accuracy of a mass measurement can be estimated by dividing the square root of the number of measurements. The error may be further reduced by applying standard statistical tests assuming the data is normally distributed (for details see ).

The terms measured accurate mass and exact mass are often used interchangeably. However, IUPAC recommends that the term measured accurate mass be used to describe an experimental quantity and calculated exact mass be used to refer to a theoretical quantity.

The mistaken belief that a kilogram of matter has the same value regardless of the gravitational environment it is in can lead to incorrect measurement. A balance, for example, will work perfectly when placed on a non-gravity surface such as the moon but will not work in space because the gravity of a planet is different. There are three main sources of error in mass measurements: environmental, procedural and human errors. This is why the use of a computer to analyse mass spectrometry data is important.

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