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Coal and petroleum are commonly called fossil fuels.
Fuels such as coal, oil and natural gas were formed over millions of years from organic matter like plankton, plants and other life forms. Over time, sand, sediment and rock buried the organic matter and it eventually formed large quantities of fuels. These underground resources, known as fossil fuels, are still the primary fuel source for electricity, heating and powering vehicles around the globe.
There are three major forms of fossil fuels: coal, oil and natural gas. All three were formed many hundreds of millions of years ago hence the name fossil fuels. The age they were formed is called the Carboniferous Period. It was part of the Paleozoic Era. "Carboniferous" gets its name from carbon, the basic element in coal and other fossil fuels.

The working-age population is typically defined as the cohort between 15 and 59 years old, excluding children and the elderly.

Exploitation often involves paying workers less than the legally mandated minimum wage, which is a common issue for vulnerable or illiterate workers.

The pulmonary artery is the artery that carries blood from the right ventricle of the heart to the lungs for oxygenation. It is involved in the pulmonary circulation of the cardiovascular system.

A reverberation, or reverb, is created when a sound or signal is reflected causing a large number of reflections to build up and then decay as the sound is absorbed by the surfaces of objects in the space which could include furniture and people, and air. 

A joint stock company has an independent status i.e. it has a separate legal entity from its members. It has an independent existence in the eyes of law and can also purchase and sell property in its own name.

Memorandum of Association is the constitution of Joint stock company. It directs or instructs joint stock company. The joint stock company runs in accordance with the memorandum of association. Activities of the joint stock company are directed by the Memorandum of Association. Memorandum of association is regarded as a blueprint as it is needed for the incorporation of the joint stock company. Memorandum of Association is submitted to Company Registrar Office. Basic information and provision of the company are clearly mentioned in the memorandum of association. It defines scopes, objectives, functions of the joint stock company.

Longitudinal waves are waves in which the motion of the individual particles of the medium is in a direction that is parallel to the direction of energy transport. Sound waves in air (and any fluid medium) are longitudinal waves because particles of the medium through which the sound is transported vibrate parallel to the direction that the sound wave moves.

The friction force is the force exerted by a surface an object moving across it. It acts in a direction to oppose the relative motion between objects.

Frictional force acts between two surfaces to oppose the relative motion between the surfaces. It acts on the body moving across it or trying to move across it.

Force can bring change in dimension.A rubber balloon expands when the molecules of air exert force on its walls.

Two plane mirrors are placed parallel in a periscope to reflect light. 

It is obvious that if the object is shifted by a distance $d$ towards the mirror, the image will also shift the same distance $d$ towards the mirror i.e., the separation between the object and the image will decrease by $2d$.

The net force is either sum or difference of individual applied forces. So, the force is either larger or smaller than individual forces.