Having consistent measurements allows scientists to work together worldwide without having to convert units. This is why the metric system is used in scientific research and technology development.
One of the seven SI base measurement units is mass. The smallest unit of mass is the kilogram (kg). A balance, like the one pictured below, is used to measure mass.
What is Mass?
It’s important to understand the difference between mass and weight. People often use these terms interchangeably, but they have different meanings. Mass is a property of matter, which includes all atoms and molecules that make up an object. Weight is a force that depends on the gravitational acceleration of an object. An object’s weight can change depending on where it is located, but its mass will remain the same.
To measure an object’s mass, scientists use a balance. While a balance is not perfect because it requires gravity to work, it gives the correct value for an object’s mass regardless of where it is in the universe. A scale might give a different result, but that is only because it relies on gravity to work.
The international standard for mass is the kilogram, one of the seven SI base measurement units. The kilogram is a special cylinder of platinum-iridium that is kept at NIST and serves as the world’s mass standard.
What is the International Prototype Kilogram?
For a century, the kilogram — or Le Grand K, as it’s known to scientists and fans of metrology — was a keystone in the International System of Units. It underpinned the definitions of four SI base units, including the gram, newton and candela; as well as a long list of derived SI units that include the pascal, sievert, farad, henry and radian.
Kept in a triple-locked vault at the BIPM on the outskirts of Paris, this standard iridium-platinum cylinder was considered to be exactly equal to one kilogram. Its weight was also the reference for all national mass standards, which were verified against it or a set of national prototypes at regular intervals.
But the IPK isn’t invariant, and comparisons of prototypes over time have shown that their masses are drifting. This has prompted a major revision of the kilogram’s definition, with a new definition based on an invariant physical constant. This change is expected to usher in innovations that will improve mass measurements in science, industry and climate study.
How is Mass Measured?
In scientific settings, mass is commonly measured with lab equipment like balances. These devices counteract the downward force of gravity and give a more accurate measure of matter.
While many people use the terms “mass” and “weight” interchangeably, they actually mean different things. Weight is the downward force exerted on an object’s matter by gravity; mass is the amount of matter in an object.
When we weigh something on a scale, we’re really measuring an unknown object’s comparison to a known object with the same weight. The scale takes the gravitational field of Earth into account and gives us a reading that tells us how much an object’s matter is worth. A balance can be used to find an object’s mass even in space or places with no gravity, since changes in gravity affect both objects on the balance equally. Mass does not depend on an object’s shape, location or size, but it is influenced by the amount of force required to accelerate it a given distance.
What is the Metric System?
Metric measurement is the worldwide standard, with only a few partial holdouts (such as the United States, which greets meters and liters with suspicion and bewilderment). Scientists all over the world use metric units for all measurements, which saves a lot of back-and-forth conversions. The metric system is based on a set of independent dimensions that exist in nature, called base units. These are the meter for length, are for area, stere for capacity, and kilogram for mass. These are augmented by derived units such as the second, ampere, degree Kelvin, and candela.
The metric system is easy to use. All metric units are related by powers of 10, so converting from one unit to another is usually just a matter of moving the decimal point a few places. In addition, all metric units share the same prefixes (kilo-, hecto-, deka-, centi-, and milli-). This allows for flexibility as well as a high level of accuracy.