Explanation: In spite of all the violent phenomenon occurring in this universe all the time, the total energy if the universe remains constant. The total energy remains constant only in an isolated system. Thus the universe is an example of an isolated system.

Explanation: It states that every body in the universe is attracted to every other body with a force directly proportional to the product of their masses and inversely proportional to the square of the distance between them. Hence it holds good in all natural processes.

Explanation: If we perform an experiment at a certain place today and repeat it after one yer at the same place, we obtain the same results. This symmetry of nature with respect to translation or displacement of time is called homogeneity of time and it leads to the law of conservation of energy

Law of nature takes the same form everywhere in the universe. That is there is no particular location in the universe. This symmetry of the laws of nature with respect to translation in space id called homogeneity of space and gives rise to the law of conservation of linear momentum.

Candela is the SI unit of luminous intensity. One candela is the luminous intensity, in a given direction, of a source that emits monochromatic radiation of frequency 540×10¹²hertz and that has a radiant intensity of 1/683 watt per sterdian in that direction.