Most scientists use the metric system for measurement. This system uses units such as the kilogram (abbreviated kg), which is the standard unit of mass.

You can measure mass with a balance-type scale or an electronic weighing instrument, or even by holding something on your hand. Mass is the amount of matter an object has and will be the same on Earth or in space.

Measuring Mass

Mass is a measure of the amount of matter in a body. It determines inertia and resistance to change in velocity, and is important in Newton’s laws of motion and Einstein’s E = m c2 equation for energy. It is usually measured using a balance.

Unlike density, which depends on an object’s size and shape, mass depends only on the type of atoms and how many of them it has. Therefore, a pineapple has the same mass as an iron bar, even though they have different densities.

Because of its dependence on physical constants, mass measurement can be difficult. It is also subject to variations due to temperature, which is why a standard kilogram has been defined as the mass of a solid prototype made from platinum and iridium, kept in a standard lab. Researchers are working to define a new kilogram that is fixed to an invariant of nature, which would make the results more stable than those of the Paris prototype.

Units of Measurement

Throughout history, many official systems of measurement have been in use. These range from the metric system in most countries to customary units still used for some day-to-day measurements, such as pounds and ounces.

For example, the unit for length in metric systems is the meter, while the units for length in customary systems are feet and inches. Units for other physical quantities, such as volume, can also be derived from these fundamental units. For instance, the liter (L) is defined as the volume occupied by a cube with sides of 1m1m on each side.

A specialized unit called the kilogram, kg, is part of the metric system and is used in all countries that have adopted the metric system. For example, the primary prototype kilogram in the United States is a platinum-iridium cylinder held at the National Institute of Standards and Technology (NIST). It replaced a physical prototype of the unit in 1875. The kilogram and the metric system are often referred to as SI units, or Standard International System of Units.

Conversions

As the world becomes more and more global, it is important to be able to convert between different systems of measurement. For example, while most people in the United States still buy gasoline by the gallon and buy apples by the pound, many companies are now selling their goods to countries that use the metric system of measurement. In these countries, the prices for things like bananas and medicines are displayed in kilograms (kg), gram (g) and milligrams (mg).

To change from one set of units to another, a conversion factor must be used. For example, to convert from inches to centimeters, you must know that 1 inch equals 2.54 cm. When converting from customary to metric, a common method of unit conversion is called dimensional analysis. This method works by comparing the numerator and denominator of the fraction to see if they cancel. Click here for a dimensional analysis applet. It also covers units of volume and capacity.

Applications

Mass measurement is used for a variety of purposes, from petrochemistry to quality control of soft drinks and alcoholic beverages. It’s also used to measure the density of a liquid, which is a standard property for determining how a fluid will react once it’s been injected into an engine.

The most common method of measuring mass is with a balance. The object to be weighed is placed on one side of the balance, while an equal amount of weight is put on the other side. This allows the known value of mass to be measured by comparing it to the unknown mass.

More sophisticated methods of measuring mass are available, such as mass spectrometry. This analytical technique identifies molecules by their molecular weight, then calculates the exact mass of each component in the sample. More recent methods such as orthogonal acceleration-time of flight (oa-TOF) mass spectrometry make exact mass measurements easier and more affordable. These techniques allow scientists to identify unknown compounds as well as quantify known ones.

From the initial weighing of raw materials to the final packaging of finished products, a food manufacturing company requires a consistent and precise weighing process. A good weighing process ensures product quality and safety guidelines are maintained throughout production.

Weighing instruments require a draft-free location, a stable bench, and calibration weights to maintain accuracy. Also, be sure to handle the instrument with clean hands to avoid fingerprints.

Weighing Equipment

Weighing equipment is used to increase efficiency and safety in a variety of industries. From the food and beverage industry to pharmaceuticals, medical devices and manufacturing, weighing equipment is necessary for accurate measurement and process control.

The type of scale required is based on the job it needs to do. Home scales work off of springs, while industrial scales can be digital or mechanical and range from platform bench scales to crane and truck scales.

The basic form of a balance is similar to a teeter totter and works on the principle that an unknown mass in a scale pan suspended from one end of a beam is balanced by a combination of known masses in scale pans or a slider weight on a linear, dial or digital display indicator. All approved scales and balances must carry an indication of accuracy which is usually found printed or stamped into a lead plug in the base. This will normally include a six-pointed star and show that the equipment was inspected and approved by trading standards services.

Weighing Procedures

Weighing is used throughout the food manufacturing process, from tracking raw materials to ensuring products are safe and high-quality. Whether you run a huge food production facility or operate a small restaurant, the quality of your product depends largely on how your weighing equipment is used and calibrated.

The way standard objects weighed are handled can significantly affect their masses. Touching the weights with bare hands leaves grease and oily films that will affect the mass at the time of measurement. Handling weights with clean forceps or a spatula of the correct size is much better.

Analytical balances are very sensitive instruments and should be operated carefully. It is best to place all weights gently in the center of the weighing pan/platform and to avoid shock loading. Dials on mechanical balances should be turned slowly and cautiously to improve repeatability. Avoid exposing the weighing system to sudden temperature changes and vibrations, and ensure it is located away from heating/cooling vents.

Calibration

Calibration is the process of adjusting an instrument to match the precision and reliability of a reference standard. Instruments can drift over time due to factors such as vibration or varying temperature and calibration removes this deviation.

Applied at the factory level, calibrating allows for savings in energy and raw materials, reduced production delays and stoppages, increased equipment longevity and optimal quality of product. Additionally, strict regulatory requirements often require traceable calibration.

Traceability refers to the ability to trace the lineage of a calibration to the primary standards maintained by a National Metrology Institute (NMI) in a given country. The BIPM works directly with NMIs to help pass down the SI for the purpose of scientific discovery and innovation, industrial manufacturing and international trade. The BIPM also maintains primary standards for several of the main SI units as well as some important derived SI units such as pressure (Pounds per Square Inch or PSI). This is referred to as the calibration pyramid.

Recording

A weighing process requires proper recording of the results. This includes recording the date and time as well as a summary of all the recorded values. A standardized method for applying significant digits and rounding techniques ensures consistency in measurement results and enables valid decision-making using data.

This includes recording that the balance is level, and that it is free of debris or foreign objects. It also includes ensuring that the weighing pan is clean and dry. For corrosive or volatile chemicals, a plastic weighing tray or other container may be required to prevent contamination of the weighing pan surface.

Weighing devices can be connected to a computer using a data cable and software for transferring the recorded weight with date and time to a file. RS-232 cable, USB virtual COM port or Bluetooth SPP (standard protocol) are the most common choices for connecting scales and balances to computers. Simple Data Logger (SDL) is software designed to send the weighing data with date and time from a scale or balance to a file, optionally adding the current date.