# Just Another Encyclopedia

## Curve

A curve is a 1-dimensional object that may be straight (like a line) or not; curves in 2-dimensional space are called plane curves, and those in 3-dimensional space are called space curves. In topology, a curve is defined by a function from an interval of the real numbers to another space. In differential geometry, the…

Radioactive decay is determined by quantum mechanics – which is inherently probabilistic. So it is impossible to work out when any particular atom will decay, but we can make predictions based on the statistical behavior of large numbers of atoms. Being unstable does not lead an atomic nucleus to emit radiation immediately. Instead, the probability…

## Law of definite proportions

Joseph Proust (1754-1826) formulated the law of definite proportions (also called the Law of Constant Composition or Proust’s Law). This law states that if a compound is broken down into its constituent elements, the masses of the constituents will always have the same proportions, regardless of the quantity or source of the original substance. Joseph Proust…

## Volume

Volume is the measure of space occupied by a three-dimensional body. The volume of a three-dimensional body is a numerical characteristic of the body; in the simplest case, when the body can be decomposed into a finite set of unit cubes (i.e., cubes with edges of unit length), it is equal to the number of…

## Isotope

Atoms of the same element with the same number of protons but a different number of neutrons (different mass numbers) are known as isotopes. The mass numbers or isotopes of an element are denoted as preceding superscripts. For example, the stable isotopes of the element oxygen are denoted 18O, 17O and 16O. Oxygen has an…

## Biogas

Biogas is a mixture of different gases produced by anaerobic decomposition (with methanogen or anaerobic organisms), or fermentation, of biomass – organic material (including animal dung, human sewage, food waste, crop residues, and industrial and municipal wastes). Biogas is a renewable energy source. It is composed primarily of methane (up to 60%), which is the combustible component, carbon…

## Star

A star (like the Sun) is an astronomical object consisting of a luminous enormous spheroid of plasma held together by its gravity, shining under its own power. Stars exist in a wide range of sizes, luminosities, temperatures, and environments. However, the single most important property of a star, which largely determines its life course, appearance,…

Ah odd number is an integer that is not divisible by 2 (without remainder). Odd numbers are: $$\pm 1, \pm 3, \pm 5, \pm 7, \pm 9, \pm 11, …$$ An integer that is not odd is called even number.