# What Is Mass Measurement?

Mass is the amount of matter in an object. It is measured in kilograms (kg) or grams, depending on the method used.

We can find the mass of an object in several ways, such as finding its WEIGHT and converting it to mass (making an assumption about standard gravity). We can also use Newton’s second law of motion to measure an object’s mass by observing how it accelerates when a force is applied to it.

## Weight

Although the terms “weight” and “matter” are often used interchangeably outside of scientific contexts, these two quantities measure different physical properties. Mass is an intrinsic property of matter, while weight is the force exerted by gravity on matter.

The metric kilogram (kg) is the standard unit of measurement for mass, while the SI pound (avoirdupois pound or U.S. customary pound) is the standard unit of measurement for force.

The important distinction is that matter has the same mass wherever it is; weight, on the other hand, is dependent on a specific gravitational field. A 6 kg lump of matter has the same weight on Earth and in a rocket far from gravity, but it would have a very different weight on Mars or Saturn. This illustrates why scientists prefer to use the term mass instead of weight. A balance scale measures the weight of an object indirectly, by comparing it to reference objects. A spring scale, on the other hand, directly measures an object’s mass by observing its push on a spring or other measuring device.

## Density

Density is the measure of the mass of a substance per unit volume. It is important in many physical applications such as pipe design, shipbuilding, helium balloons and even to solve crimes (Archimedes used it around 250 BCE to reveal that a craftsman defrauded the king by replacing gold with silver).

In general, solids are denser than liquids, which are in turn less dense than gases. However, the density of a particular material may be affected by its temperature and pressure.

Because of this, the density of a solid or liquid must be measured using a balance and a reference liquid of known density. Various techniques exist for measurement of density including the use of a hydrometer, a dasymeter, a buoyancy balance, an immersed body method and a pycnometer. The limiting factor in measuring the density of a solid is limited wettability (the ability to absorb water). This can be overcome by adding a few drops of wetting agent to the reference liquid.

## Volume

While determining an object’s mass is straightforward with a balance, determining its volume can be more challenging. While it is easy to measure the volume of solids with a regular shape, like a cube, by multiplying length by width by height, it’s more complicated for irregular shapes.

Liquid volumes are also easy to determine with a burette or graduated cylinder for chemistry lab measurements or a standard measuring cup and spoon for everyday use. Gases are a little different, since they expand to fit their container, but even though it’s more difficult to measure, it can still be done with the same basic methods.

It’s important to understand the interplay between mass and volume. In order to accurately determine the density of an object, it is necessary to know its mass and its volume. This is particularly true when comparing two different substances that have the same weight, but differ in volume. Using the principles of Archimedes, you can find out which one has the higher density by calculating the amount of water it would take to equalize the volumes of the two objects.

## Temperature

Temperature is one of the intensive properties of matter – it is related to the kinetic energy of vibrating and colliding particles making up the material. It also reflects the amount of heat energy that can spontaneously flow from one body to another.

The choice of the reference temperature is a key one for length measurements. For example, if two mating parts of different materials (say steel and brass) are assembled at the same temperature, they will be their nominal sizes because their coefficients of thermal expansion will be the same at that temperature. But if the parts are assembled at a different temperature, they will grow or shrink by the difference in their CTEs times the difference in temperature.

This is why the reference temperature for dimensional measurements is 20 degC. It may seem arbitrary but it was a result of many years of thought and discussion. It is also a result of the fact that temperature measurement is closely tied to thermometers and their construction.

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