# The Basics of Mass Measurement

In physics, the concept of mass is sometimes confused with weight. Both measure the amount of matter contained in an object or particle. However, weight changes depending on gravity while mass remains the same in any environment.

When determining an objectâ€™s mass cannot be done on a balance, transducers are used to measure mass properties. They send a signal to a processor that makes mass calculations.

## Definition

Many people are confused about the difference between mass and weight. While both are proportional to each other, they are different measurements of different physical properties. Weight is a measure of the force exerted by gravity on something, while mass is a measurement of the amount of matter an object contains. An object’s weight changes if it is moved to another planet, but its mass remains the same.

The most common method for measuring mass is through a balance. The unknown mass of an object is compared with a known value of mass to obtain its measure. A balance works in space and places with no gravity as well, since changes in gravitational acceleration affect both masses equally on the balance. Mass is also measured in a specialized way called inertial mass, which is based on an object’s resistance to acceleration. It is important to teach kids the difference between these two measurements so they are better prepared for more advanced science and mathematics later in school.

## Units

Students should be familiar with the basic units used in measurement such as the meter (length), gram (mass), and liter (volume). They should also be aware that these base units are related to each other.

For example, the metric unit of volume is equal to one cubic centimeter. The meter is the base unit of length, and it can be divided into smaller units like millimeters or micrometers. These smaller units are related to the meter by a ratio called a decimal.

The kilogram is the only SI base unit that is defined based on a physical artifact, though it’s proposed to redefine the kilogram in terms of a fixed value for the Planck constant, a fundamental quantity of nature. Other common metric units include the tonne (or metric ton) and the electronvolt, which is useful in measuring atomic properties. Units can be multiplied together or divided to generate new units for quantities such as velocity, which is calculated by dividing a distance quantity by a time quantity.

## Measurement

The most common way to measure mass is to use a balance. The unknown object is placed on the fulcrum of the balance and then a standard object (with known mass) is added to counterbalance it at one end. The mass of the unknown object is then calculated by comparing it to the standard mass.

Another method is to find the density of the object. Density is an indication of how tightly packed together the matter is in an object. It is commonly measured in kilograms per cubic meter, i.e. kg/m3, or in grams per cubic centimeter, i.e. g/cm3 for smaller objects.

The most important thing to remember when measuring mass is that it measures the amount of matter in an object and does not depend on gravity. This is why an object’s weight may change when it is moved to another planet, but the object will still have the same mass. It is also why a bomb has such a large gravitational pull while a pineapple does not.

## Calculation

Generally, the most common tool to measure mass is a balance. Researchers and ordinary people use this device all the time to determine the weight of things like paperclips and bottles of water. The difference is that the tool only works in a no-gravity environment and if you move the object to a different planet, the weight will change.

Mass spectrometers are used to obtain very high resolution mass measurements. This is measured as the ability of the instrument to distinguish closely spaced peaks in the mass spectrum (see the figure below). The higher the resolution, the better.

Accurate mass measurements are essential in many scientific fields, such as identifying unknown impurities for biomolecules and determining the elemental formula of complex molecules from their peptide fragments produced during digestion. The accuracy of the measurement is determined by how close it gets to the calculated exact mass of an ion. When the error is very small, a unique empirical formula can be unambiguously assigned to the ion.

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