Energy density in the context of "Protein in nutrition"

The Big Bang is a physical theory that describes how the universe expanded from an initial state of high density and temperature. Various cosmological models based on the Big Bang concept explain a broad range of phenomena, including the abundance of light elements, the cosmic microwave background (CMB) radiation, and large-scale structure. The uniformity of the universe, known as the horizon and flatness problems, is explained through cosmic inflation: a phase of accelerated expansion during the earliest stages. Detailed measurements of the expansion rate of the universe place the initial singularity at an estimated 13.787±0.02 billion years ago, which is considered the age of the universe. A wide range of empirical evidence strongly favors the Big Bang event, which is now widely accepted.

Extrapolating this cosmic expansion backward in time using the known laws of physics, the models describe an extraordinarily hot and dense primordial universe. Physics lacks a widely accepted theory that can model the earliest conditions of the Big Bang. As the universe expanded, it cooled sufficiently to allow the formation of subatomic particles, and later atoms. These primordial elements—mostly hydrogen, with some helium and lithium—then coalesced under the force of gravity aided by dark matter, forming early stars and galaxies. Measurements of the redshifts of supernovae indicate that the expansion of the universe is accelerating, an observation attributed to a concept called dark energy.

Various alcohols are used as fuel for internal combustion engines. The first four aliphatic alcohols (methanol, ethanol, propanol, and butanol) are of interest as fuels because they can be synthesized chemically or biologically, and they have characteristics which allow them to be used in internal combustion engines. The general chemical formula for alcohol fuel is C_nH_2n+1OH.

Most methanol is produced from natural gas, although it can be produced from biomass using very similar chemical processes. Ethanol is commonly produced from biological material through fermentation processes. Biobutanol has the advantage in combustion engines in that its energy density is closer to gasoline than the simpler alcohols (while still retaining over 25% higher octane rating); however, biobutanol is currently more difficult to produce than ethanol or methanol. When obtained from biological materials and/or biological processes, they are known as bioalcohols (e.g. "bioethanol"). There is no chemical difference between biologically produced and chemically produced alcohols.

Proteins are essential nutrients for the human body. They are one of the constituents of body tissue and also serve as a fuel source. As fuel, proteins have the same energy density as carbohydrates: 17 kJ (4 kcal) per gram. The defining characteristic of protein from a nutritional standpoint is its amino acid composition.

Proteins are polymer chains made of amino acids linked by peptide bonds. During human digestion, proteins are broken down in the stomach into smaller polypeptide chains via hydrochloric acid and protease actions. This is crucial for the absorption of the essential amino acids that cannot be biosynthesized by the body.

An atomic battery, nuclear battery, radioisotope battery or radioisotope generator uses energy from the decay of a radioactive isotope to generate electricity. Like a nuclear reactor, it generates electricity from nuclear energy, but it differs by not using a chain reaction. Although commonly called batteries, atomic batteries are technically not electrochemical and cannot be charged or recharged. Although they are very costly, they have extremely long lives and high energy density, so they are typically used as power sources for equipment that must operate unattended for long periods, such as spacecraft, pacemakers, medical devices, underwater systems, and automated scientific stations in remote parts of the world.

Nuclear batteries began in 1913, when Henry Moseley first demonstrated a current generated by charged-particle radiation. Since RCA's initial nuclear research and development in the early 1950s, many types and methods have been designed to extract electrical energy from nuclear sources.

In fluid dynamics, wave shoaling is the effect by which surface waves, entering shallower water, increase in wave height. It is caused by the fact that the group velocity, which is also the wave-energy transport velocity, decreases with water depth. Under stationary conditions, a decrease in transport speed must be compensated by an increase in energy density in order to maintain a constant energy flux. Shoaling waves will also exhibit a reduction in wavelength while the frequency remains constant.

In other words, as the waves approach the shore and the water gets shallower, the waves get taller, slow down, and get closer together.

Coal mining in the United Kingdom dates back to Roman times and occurred in many different parts of the country. Britain's coalfields are associated with Northumberland and Durham, North and South Wales, Yorkshire, the Scottish Central Belt, Lancashire, Cumbria, the East and West Midlands and Kent. After 1972, coal mining quickly collapsed and had practically disappeared by the 21st century. Production fell from 228 million tonnes in 1957 to just 107 thousand tonnes in 2024, while coal consumption fell from 216 million to 2 million tonnes in the same time period. Employment in coal mines fell from a peak of 1,191,000 in 1920 to 695,000 in 1956, 247,000 in 1976, 44,000 in 1993, 2,000 in 2015, and to 360 in 2022.

Almost all onshore coal resources in the UK occur in rocks of the Carboniferous period, some of which extend under the North Sea. Bituminous coal is present in most of Britain's coalfields and is 86% to 88% carbon. In Northern Ireland, there are extensive deposits of lignite which is less energy-dense based on oxidation (combustion) at ordinary combustion temperatures. In 2015, EURACOAL estimated that the UK has 3.56 billion tonnes of hard coal resources.

Specific energy or massic energy is energy per unit mass. It is also known as gravimetric energy density, which is not to be confused with energy density, which is defined as energy per unit volume. It is used to quantify, for example, stored heat and other thermodynamic properties of substances such as specific internal energy, specific enthalpy, specific Gibbs free energy, and specific Helmholtz free energy. It may also be used for the kinetic energy or potential energy of a body. Specific energy is an intensive property, whereas energy and mass are extensive properties.

The SI unit for specific energy is the joule per kilogram (J/kg). Other units still in use worldwide in some contexts are the kilocalorie per gram (Cal/g or kcal/g), mostly in food-related topics, and watt-hours per kilogram (W⋅h/kg) in the field of batteries. In some countries the Imperial unit BTU per pound (Btu/lb) is used in some engineering and applied technical fields.

In cosmology, the equation of state of a perfect fluid is characterized by a dimensionless number ${\displaystyle w}$, equal to the ratio of its pressure ${\displaystyle p}$ to its energy density ${\displaystyle \rho }$: $${\displaystyle w\equiv {\frac {p}{\rho }}.}$$It is closely related to the thermodynamic equation of state and ideal gas law.

A lithium-ion battery, or Li-ion battery, is a type of rechargeable battery that uses the reversible intercalation of Li ions into electronically conducting solids to store energy. Li-ion batteries are characterized by higher specific energy, energy density, and energy efficiency and a longer cycle life and calendar life than other types of rechargeable batteries. Also noteworthy is a dramatic improvement in lithium-ion battery properties after their market introduction in 1991; over the following 30 years, their volumetric energy density increased threefold while their cost dropped tenfold. In late 2024 global demand passed 1 terawatt-hour per year, while production capacity was more than twice that.

The invention and commercialization of Li-ion batteries has had a large impact on technology, as recognized by the 2019 Nobel Prize in Chemistry.Li-ion batteries have enabled portable consumer electronics, laptop computers, cellular phones, and electric cars. Li-ion batteries also see significant use for grid-scale energy storage as well as military and aerospace applications.