Mass measurement is all around us, and it’s something that children should learn early. This will help them effortlessly grasp physics concepts later in school.
The first thing to understand is that mass is not the same as weight. Your weight changes depending on where you are — your body is heavier when curled up on the couch than when stretching as high as you can.
The metric system
The metric system is the measurement system used by most countries. It is also the system of choice for scientists and engineers. It is a decimal-based system that uses multiples of 10. This makes conversions between metric units relatively simple, even down to the smallest unit, the gram.
The meter is the base unit for length, the kilogram is the base unit for mass, and the litre is the base unit for volume. Each of these base units has derived units (for areas, densities, temperatures) that are built on them.
There are twenty-four metric prefixes (kilo-, hecto-, deka-, centi-, and deci-) that can be combined with these base units to form other metric units. The metric system is often thought to be difficult because of all the different units and symbols that it has. However, it is very easy to use if you take the time to learn it. Using a metric tape measure, measuring objects in metric units, and weighing yourself on a metric scale are good ways to get started.
The kilogram
When measuring something, we want to know the exact amount. So we use scales. But it turns out that scales aren’t always accurate enough. For some applications — such as testing medication, developing new materials or analyzing the environment — we need to be able to measure to parts-per-billion accuracy. This is why scientists decided to redefine the kilogram in November 2018.
Instead of comparing the gravitational force on an object to that of a golf-ball-sized metal artifact called Le Grand K, which lives at the International Bureau of Weights and Measures (BIPM) in Sevres, France, we will compare it to a precise value of a fundamental constant of nature.
It is a move that will end the era of human-scale physical objects defining measurement units like length, time and mass. It will also set the stage for a future in which all seven SI base units — the meter for distance, the second for time, the kilogram for mass, the mole for amount of substance, the ampere for electrical current and the kelvin for temperature and luminosity — are defined by comparison to a single, fundamental constant of nature.
The meter
The meter is the key to accurate mass flow measurement. This measure differs from volumetric flow rate, as it identifies mass per time rather than fluid volume. It is used in many critical applications throughout industry, including recipe formulation, material balance determinations, billing and custody transfer operations.
The Coriolis meter is one of the most accurate mass flow meters available for clean or corrosive gases and liquids, especially in supercritical applications. This gyroscopic meter utilizes motion mechanics to directly measure mass flow, density and temperature.
The meter’s sensor tubes are separated by a splitter with drive coils installed in the middle and detection coils at both ends. When excitation power is applied to the coils, they induce vibration in the sensor tubes that produce a twist in the tube deflection (spring torsion) proportional to the product’s mass flow. This two-tube design reduces external vibration interference and the amount of power required to initiate tube vibration. However, the thin-walled sensor tubes are susceptible to degradation from pitting, cracking, coating, erosion and corrosion that cause shifts in the meter calibration factor over time.
The second law of thermodynamics
Most physical laws take the form of an equation that describes precisely what must happen in a particular situation. The second law of thermodynamics, however, is an inequality that imposes additional restrictions on processes.
It states that all processes that involve the transfer or conversion of energy cannot be truly reversible. This means that in a closed system, the average entropy of that system must always increase, as is evidenced by friction and other irreversible phenomena.
While the Second Law may seem inconvenient, it is essential to life on Earth. For example, in order for the proteins and nucleic acids that make up a human cell to be able to function properly, they must be assembled from much smaller molecules such as amino acids and nucleotides.
This assembly process requires heat, which is an increase in the entropy of the surrounding environment. Thus, the formation of a protein or nucleotide requires that energy be transferred from the surroundings to the new molecules. Inevitably, the entropy of the surrounding environment will therefore increase by an amount equal to the heat energy transferred.