Physicists create world's smallest engine

Theoretical physicists at Trinity College Dublin are among an international collaboration that has built the world's smallest engine—which, as a single calcium ion, is approximately ten billion times smaller than a car ...

What the climate crisis means for land rights

The climate crisis will reshape our relationships to land around the world. Journalist David Wallace-Wells warns that, once the planet warms 2°C above preindustrial levels—the target set by the Paris Agreement—"major ...

Watching electrons using extreme ultraviolet light

A new technique developed by a team at MIT can map the complete electronic band structure of materials at high resolution. This capability is usually exclusive to large synchrotron facilities, but now it is available as a ...

These migratory birds will risk their lives for a good nap

When driving across country, people can only make it so far before stopping off to rest. Likewise, most migratory songbirds must make stops during their long-distance journeys to sleep along the way. Now, researchers have ...

Ammonia for fuel cells

Fuel cells are pollution-free power sources that convert chemical energy to electricity with high efficiency and zero emissions. Fuel cell cars, trucks, and buses would allow people to travel long distances with convenient ...

Shift to renewable electricity a win-win at statewide level

Amid rollbacks of the Clean Power Plan and other environmental regulations at the federal level, several U.S. states, cities, and towns have resolved to take matters into their own hands and implement policies to promote ...

Electronic waste is mined for rare earth elements

Rare earth elements are the "secret sauce" of numerous advanced materials for energy, transportation, defense and communications applications. Their largest use for clean energy is in permanent magnets, which retain magnetic ...

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Energy

In physics, energy (from the Greek ἐνέργεια - energeia, "activity, operation", from ἐνεργός - energos, "active, working") is a scalar physical quantity that describes the amount of work that can be performed by a force, an attribute of objects and systems that is subject to a conservation law. Different forms of energy include kinetic, potential, thermal, gravitational, sound, light, elastic, and electromagnetic energy. The forms of energy are often named after a related force.

Any form of energy can be transformed into another form, but the total energy always remains the same. This principle, the conservation of energy, was first postulated in the early 19th century, and applies to any isolated system. According to Noether's theorem, the conservation of energy is a consequence of the fact that the laws of physics do not change over time.

Although the total energy of a system does not change with time, its value may depend on the frame of reference. For example, a seated passenger in a moving airplane has zero kinetic energy relative to the airplane, but non-zero kinetic energy relative to the Earth.

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