The first step in measuring an object’s mass is to collect all its dimensions. This includes length, which metrologists (or measurement experts) use to derive other measurements such as volume.

Unlike weight, which changes due to gravity, mass remains the same no matter where an object is. It’s a property of matter based on its atomic and molecular makeup.

Definition

Mass is a physical property of matter. It is determined by the atomic and molecular makeup of an object. For example, a pine tree has more mass than a baseball bat, because it is made up of more atoms.

The basic unit for measuring mass is the kilogram (kg). A regular-sized paperclip has a mass of about 1 gram.

Measuring mass is usually done by using a balance scale. The unknown mass is placed on one side of the scale and its value is obtained by comparing it with a known quantity. This type of scale is unaffected by changes in gravity.

The kilogram became a standard measurement unit in the metric system when it was introduced in 1875. Since then, a number of other base units have been defined, such as the meter for lengths, the stere for areas, and the litre for liquid capacities. These derived units are all related to the kilogram through factors of powers of 10. The kilogram is still defined by an artifact, the International Prototype Kilogram, which is a metal cylinder stored in the National Institute of Standards and Technology in the United States.

Concepts

The basic unit for mass is kilogram, or kg. This SI unit, along with metre (100 cm) for length, aretonne (one hundred ares) for area, stere (1 m3) for dry capacity and litre (one dm3) for liquid capacity make up the standard metric system of units used worldwide.

A balance is the most common tool used to measure an object’s mass. It compares the unknown object’s weight with that of a known mass to determine an object’s relative gravitational weight. This method of mass measurement works even in places without gravity since changes in gravitational acceleration affect both masses equally.

To help students understand that weight and mass are different concepts and measurements, try letting them hold a pen and a bottle of water in each hand. They should realize that the bottle of water feels heavier than the pen because it has more mass. Using a scale, they can then measure the objects’ respective masses.

Examples

Most people are familiar with measuring the weight of items using a scale or balance. What many people don’t know is that these balances can also measure mass directly.

The basic SI unit of mass is the kilogram, kg, though smaller masses are often measured in grams (g). Mass may be measured with a lab instrument like the triple beam balance pictured below, or it can be calculated from an object’s density and its volume.

One of the most important examples of mass is an individual human’s weight, which depends on the gravitational pull of the Earth. An identical body would weigh less on Mars or more on Saturn, because gravity there is different. However, its mass would be the same on all planets because it is a property of matter. This is why it’s essential to understand the difference between mass and weight! Mass and weight are very similar, so it’s easy to confuse the two.

Applications

In laboratory work, mass measurements are important for many fields. For example, chemical engineers often convert mass data to a force (measured in newtons) to determine the amount of energy required to move an object. This calculation is based on the principle that mass and weight are related: an object’s mass is proportional to the gravitational acceleration exerted on it.

Other examples include forensic analysis (e.g., trace evidence in arson cases), food contamination testing, pesticide residue analysis, protein identification and carbon dating. In biochemistry, high-resolution mass spectrometry can be used to characterize oligomerization and aggregation of biological molecules, measure stoichiometries in reactions, and quantify molecular interactions (Soltermann, et al. 2021).

NIST is working with Snap-on Inc. to develop a tabletop version of our Kibble balance for use in the field, allowing the Army to eliminate the need to send equipment to NIST for mass calibrations that are directly traceable to the SI kilogram standard. The collaboration demonstrates NIST’s commitment to making mass measurement easier and more accessible to military and civilian users.

Weighing is a vital process that must be done properly for accurate results. Many factors can affect weighing including the operating surroundings, the sensitivity of the balance and the sample to be weighed.

For example, the air temperature of the weighing area should be the same as the temperature of the sample to prevent air currents that can affect the results. Good laboratory practices and standards are also important.

Accuracy

Accurate weight measurement is essential for industrial operations to ensure that processes are optimised, efficient and compliant with safety standards. It helps reduce waste by ensuring that raw materials are used effectively, minimising the likelihood of overproduction and cutting costs associated with costly corrections or reworks.

For accurate weighing, the balance should be properly calibrated and the environment should be well ventilated to avoid air currents. It is also important to select the right sensitivity weight for the application and use it correctly to minimise errors.

The accuracy of the weighing process depends on several factors, including balance drift, calibration, temperature variations, magnetic and electrostatic fields, sample characteristics (evaporation, hygroscopic/hydrophobic solid materials gaining or losing moisture) and manipulative skills during weighing. By working with reputable scale suppliers, utilising modern technology and implementing effective maintenance practices, organisations can maximise the benefits of an accurate weighing system. For example, accurate measurements ensure that ingredients are added in the correct sequence and proportion to maintain product quality.

Efficiency

Weighing operations are executed by using a variety of equipment including proper containers, receiving vessels, forceps, pipets and spatulas. If a quantity is too large for direct weighing, counting by weighing may be employed. In this case, the operator subtracts a certain amount from a full container until the desired reading is achieved on the balance pan.

In food production applications, accurate weighing is critical to ensure that all ingredients are distributed evenly and the end product looks and tastes the same each time. Garber offers a wide array of process weighing solutions including loss in weight controllers that connect to your enterprise resource planning system and help you understand the loss in weight of ingredients as they are weighed in your hoppers.

When performing direct weighing, a substance ought to be added directly into a tared container which will hold it rather than placed on the balance pan itself. This prevents air currents from affecting the weighing results. It is also important to exercise the balance before taking a reading.

Safety

Weighing systems can contain heavy components that must be handled safely. Keeping an eye on the area where they are located and ensuring that all individuals working on them wear proper PPE (personal protective equipment) helps to prevent accidental injury.

Environmental considerations must also be taken into account, particularly when working with hazardous chemicals. Fume hoods and safety cabinets help to keep dangerous substances contained, while gloves and appropriate ventilation systems can minimize any exposure. It is also important to use a device that can eliminate electrostatic charge from fine powders, as this can cause erroneous readings on precision balances.

Another technique that can help reduce error is weighing by difference. This involves weighing the container with its contents and then subtracting the weight of the substance that is to be removed from the total. The process can eliminate errors caused by initial readings on a balance as any mistakes are cancelled out when subtraction is performed.

Maintenance

Observing strict laboratory rules will help minimize errors in the weighing process. For example, a balance should not be touched with bare hands. Moisture, grease and dirt on the fingertips can affect the weight reading. Handling large objects or containers is also problematic, especially with lower tolerance classes. In these cases, special hoists and crane hydraulics are available to safely set the weight on the balance.

In order to prevent balance drift, it is recommended that the balance be calibrated on a regular basis using a check-weight of known mass at the current ambient temperature. Some electronic analytical balances require a “tare” button to be pressed before each weighing.

It is also helpful to test the weighing system with the actual material it will handle during normal operation. This will simulate handling dynamics and give a more realistic picture of its performance. This information can be used to make adjustments and improvements in the weighing system’s calibration.