Mass

Jai Ganesh · 2024-12-22 16:17:57

Mass

Gist

Mass, in physics, is the quantitative measure of inertia, a fundamental property of all matter. It is, in effect, the resistance that a body of matter offers to a change in its speed or position upon the application of a force. The greater the mass of a body, the smaller the change produced by an applied force.

Summary

The unit of mass in the International System of Units (SI) is the kilogram, which is defined in terms of Planck’s constant, which is defined as equal to 6.62607015 × {10}^{-34} joule second. One joule is equal to one kilogram times metre squared per second squared. With the second and the metre already defined in terms of other physical constants, the kilogram is determined by accurate measurements of Planck’s constant. (Until 2019 the kilogram was defined by a platinum-iridium cylinder called the International Prototype Kilogram kept at the International Bureau of Weights and Measures in Sèvres, France.) In the English system of measurement, the unit of mass is the slug, a mass whose weight at sea level is 32.17 pounds.

Weight, though related to mass, nonetheless differs from the latter. Weight essentially constitutes the force exerted on matter by the gravitational attraction of Earth, and so it varies slightly from place to place. In contrast, mass remains constant regardless of its location under ordinary circumstances. A satellite launched into space, for example, weighs increasingly less the farther it travels away from Earth. Its mass, however, stays the same.

According to the principle of conservation of mass, the mass of an object or collection of objects never changes, no matter how the constituent parts rearrange themselves. If a body split into pieces, the mass divides with the pieces, so that the sum of the masses of the individual pieces is equal to the original mass. Or, if particles are joined together, the mass of the composite is equal to the sum of the masses of the constituent particles. However, this principle is not always correct.

With the advent of the special theory of relativity by Einstein in 1905, the notion of mass underwent a radical revision. Mass lost its absoluteness. The mass of an object was seen to be equivalent to energy, to be interconvertible with energy, and to increase significantly at exceedingly high speeds near that of light (about 3 × {10}^{8} metres per second, or 186,000 miles per second). The total energy of an object was understood to comprise its rest mass as well as its increase of mass caused by high speed. The rest mass of an atomic nucleus was discovered to be measurably smaller than the sum of the rest masses of its constituent neutrons and protons. Mass was no longer considered constant, or unchangeable. In both chemical and nuclear reactions, some conversion between mass and energy occurs, so that the products generally have smaller or greater mass than the reactants. The difference in mass is so slight for ordinary chemical reactions that mass conservation may be invoked as a practical principle for predicting the mass of products. Mass conservation is invalid, however, for the behaviour of masses actively involved in nuclear reactors, in particle accelerators, and in the thermonuclear reactions in the Sun and stars. The new conservation principle is the conservation of mass-energy.

Details

Mass is an intrinsic property of a body. It was traditionally believed to be related to the quantity of matter in a body, until the discovery of the atom and particle physics. It was found that different atoms and different elementary particles, theoretically with the same amount of matter, have nonetheless different masses. Mass in modern physics has multiple definitions which are conceptually distinct, but physically equivalent. Mass can be experimentally defined as a measure of the body's inertia, meaning the resistance to acceleration (change of velocity) when a net force is applied. The object's mass also determines the strength of its gravitational attraction to other bodies.

The SI base unit of mass is the kilogram (kg). In physics, mass is not the same as weight, even though mass is often determined by measuring the object's weight using a spring scale, rather than balance scale comparing it directly with known masses. An object on the Moon would weigh less than it does on Earth because of the lower gravity, but it would still have the same mass. This is because weight is a force, while mass is the property that (along with gravity) determines the strength of this force.

In the Standard Model of physics, the mass of elementary particles is believed to be a result of their coupling with the Higgs boson in what is known as the Brout–Englert–Higgs mechanism.

Phenomena

There are several distinct phenomena that can be used to measure mass. Although some theorists have speculated that some of these phenomena could be independent of each other, current experiments have found no difference in results regardless of how it is measured:

* Inertial mass measures an object's resistance to being accelerated by a force (represented by the relationship F = ma).
* Active gravitational mass determines the strength of the gravitational field generated by an object.
* Passive gravitational mass measures the gravitational force exerted on an object in a known gravitational field.

The mass of an object determines its acceleration in the presence of an applied force. The inertia and the inertial mass describe this property of physical bodies at the qualitative and quantitative level respectively. According to Newton's second law of motion, if a body of fixed mass m is subjected to a single force F, its acceleration a is given by F/m. Repeated experiments since the 17th century have demonstrated that inertial and gravitational mass are identical; since 1915, this observation has been incorporated a priori in the equivalence principle of general relativity.

Units of mass

The International System of Units (SI) unit of mass is the kilogram (kg). The kilogram is 1000 grams (g), and was first defined in 1795 as the mass of one cubic decimetre of water at the melting point of ice. However, because precise measurement of a cubic decimetre of water at the specified temperature and pressure was difficult, in 1889 the kilogram was redefined as the mass of a metal object, and thus became independent of the metre and the properties of water, this being a copper prototype of the grave in 1793, the platinum Kilogramme des Archives in 1799, and the platinum–iridium International Prototype of the Kilogram (IPK) in 1889.

However, the mass of the IPK and its national copies have been found to drift over time. The re-definition of the kilogram and several other units came into effect on 20 May 2019, following a final vote by the CGPM in November 2018. The new definition uses only invariant quantities of nature: the speed of light, the caesium hyperfine frequency, the Planck constant and the elementary charge.

(General Conference on Weights and Measures (abbreviated CGPM from the French: Conférence générale des poids et mesures))

Additional Information

The mass of an object is a measure of the amount of matter it has. A mountain has a greater mass than a rock, while mass is different weight, which is the vector (directional) product of mass and gravitational acceleration, e.g. 9.81 m{s}^{-2}. Weight is sometimes called the force of gravity.

The mass of an object is measurable when a force is exerted on the object. If the mass is greater, the object will have less acceleration (changes in velocity), which is sometimes called inertial mass as it measures the inertia.

A gigantic mass, like our planet Earth, attracts such a smaller mass as human being to keep the human being from floating away from the Earth's surface. "Mass attraction" is another word for gravity, a force existing between all matters. When measuring the force of gravity exerted on an object, its gravitational mass can be found. Tests of inertial and gravitational mass show that they are the same or almost the same.

Units of mass

The unit of mass in the International System of Units is the kilogram, which is represented by the symbol 'kg'. Fractions and multiples of this basic unit include the gram (one thousandth of a kg, symbol 'g') and the tonne (one thousand kg), amongst many others.

In some fields or applications, it is convenient to use different units to simplify the discussions or writings. For instance,

* Atomic physicists deal with the tiny masses of individual atoms and measure them in atomic mass units.
* Jewelers normally work with small jewels and precious stones where masses are traditionally measured in carats, which correspond to 200 mg or 0.2 g.
* The masses of stars are very large and are sometimes expressed in units of solar masses.

Traditional units are still in encountered in some countries: imperial units such as the ounce or the pound were in widespread use within the British Empire. Some of them are still popular in the United States, which also uses units like the short ton (2,000 pounds, 907 kg) and the long ton (2,240 pounds, 1010 kg), not to be confused with the metric ton (1,000 kg).

The Quantum Concept of Mass

In atomic nuclei, example in protons and neutrons,the residual mass comes from the binding kinetic and potential energy of the quarks and gluon field. An analogy to go along with is to think of the 3 quarks as balls with the gluons as a spring connecting the quarks. This mass accounts for 99% of the mass of these baryons with the remaining 1% coming from the individual quarks which comes from quantum interactions with the Higgs field.

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#1 2024-12-22 16:17:57

Mass

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