Kids are naturally inquisitive, and introducing them to the concept of mass early will help them easily grasp more advanced concepts like physics later. Start by asking them which object feels heavier: a pen or a bottle of water?
Inertial mass is a property of objects that can be determined by weighing them. However, the measurement is complicated by the need for accurate and stable sets of standard weights that are subject to physical damage, chemical attack, and loss.
Physical
The most basic method for measuring mass is to use a balance. A balance consists of a crossbeam from which two pans are suspended to hold the masses to be compared. The unknown mass is placed in one of the pans and the known masses are added to it until the scale returns to its neutrality point.
The measurement of an object’s weight is related to its mass, but it doesn’t necessarily mean that the same amount of matter is present in each case. For example, your weight will differ depending on whether you are on Earth or the Moon, but your mass won’t. This is why it’s important to distinguish between the terms weight and mass. The latter can be measured using a balance, while the former is only accessible through gravity.
Chemical
Chemical weighing instruments are used in laboratories for measuring the mass of chemicals, such as pharmaceutical compounds and heavy metals. The balances are typically based on analytical or semi-micro models, and provide very high levels of accuracy and precision.
In the absence of systematic errors, a larger number of experimental measurements will bring the mean value closer to the calculated exact mass. This is because the experimental error sample distribution will tend to normalise with the number of observations and the standard deviation, s, reduces towards zero.
When reporting accurate masses, the mass list should be quoted to one decimal place where possible. This will ensure that rounding errors do not arise in subsequent calculations. This is recommended in conjunction with statistical tests that verify the underlying data distribution.
Molecular
The chemistry of molecules is fundamentally dependent on molecular mass measurement. In the laboratory a chemist typically weighs their chemicals in grams and must know how many molecules of each element are present. The mole is a bridge between the atomic world (amu) and the lab scale (grams). It allows the chemist to translate the number of atoms in a sample into its mass in grams, provided they have the instrumentation that can measure the relative molar mass of the constituent ions or molecules.
In mass spectrometry this is most often accomplished via the m/z value, where m is the mass of the molecular ion and z is its charge. High m/z accuracy is essential for accurate measurement of the relative molecular masses of unmodified synthetic and natural biomolecules.
Active Gravitational
A gravimeter measures absolute gravity by determining the acceleration of a test mass free falling in a vacuum. The test mass includes a retroreflector and terminates one arm of a Michelson interferometer, which is calibrated with an atomic clock to eliminate distortion from air resistance, vibration, and magnetic forces.
Galileo and Newton showed that inertial and gravitational mass are the same; their results are incorporated into Einstein’s theory of general relativity as the weak equivalence principle. Repeated experiments since then have verified this equivalence, as well as the fact that the force of gravitation varies with time. This makes gravity well suited for measurement, using the same principles as simple spring scales that measure weight, taking g into account. The Tsiolkovsky State Museum of Cosmonautics uses a gravimeter to determine an astronaut’s inertial mass while in weightlessness.
Passive Gravitational
Passive gravitational mass measures the response of an object to gravity. It is measured by allowing a test mass to fall freely, with its position precisely determined using an interferometer and timed with an atomic clock.
These devices, called absolute gravimeters, can measure a test object’s free-fall acceleration with an accuracy of 2 ppb. Such measurements verify the weak equivalence principle, which states that passive gravitational and inertial masses are proportional, independent of an object’s material composition.
This equivalence principle is crucial to Einstein’s theory of relativity, which depends on the weak equivalence of gravitational and inertial mass. It also explains why objects of different materials that react to the same force have the same weight. This result is the basis for our concept of mass.