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Physics is the natural science that studies matter, its fundamental constituents, its motion and behavior through space and time, and the related entities of energy and force. Physics is one of the most fundamental scientific disciplines, with its main goal being to understand how the universe behaves. A scientist who specializes in the field of physics is called a physicist.
Physics is one of the oldest academic disciplines and, through its inclusion of astronomy, perhaps the oldest. Over much of the past two millennia, physics, chemistry, biology, and certain branches of mathematics were a part of natural philosophy, but during the Scientific Revolution in the 17th century these natural sciences emerged as unique research endeavors in their own right. Physics intersects with many interdisciplinary areas of research, such as biophysics and quantum chemistry, and the boundaries of physics are not rigidly defined. New ideas in physics often explain the fundamental mechanisms studied by other sciences and suggest new avenues of research in these and other academic disciplines such as mathematics and philosophy.
Advances in physics often enable advances in new technologies. For example, advances in the understanding of electromagnetism, solid-state physics, and nuclear physics led directly to the development of new products that have dramatically transformed modern-day society, such as television, computers, domestic appliances, and nuclear weapons; advances in thermodynamics led to the development of industrialization; and advances in mechanics inspired the development of calculus. (Full article...)
A calutron is a mass spectrometer originally designed and used for separating the isotopes of uranium. It was developed by Ernest Lawrence during the Manhattan Project and was based on his earlier invention, the cyclotron. Its name was derived from California University Cyclotron, in tribute to Lawrence's institution, the University of California, where it was invented. Calutrons were used in the industrial-scale Y-12 uranium enrichment plant at the Clinton Engineer Works in Oak Ridge, Tennessee. The enriched uranium produced was used in the Little Boy atomic bomb that was detonated over Hiroshima on 6 August 1945.
The calutron is a type of sector mass spectrometer, an instrument in which a sample is ionized and then accelerated by electric fields and deflected by magnetic fields. The ions ultimately collide with a plate and produce a measurable electric current. Since the ions of the different isotopes have the same electric charge but different masses, the heavier isotopes are deflected less by the magnetic field, causing the beam of particles to separate into several beams by mass, striking the plate at different locations. The mass of the ions can be calculated according to the strength of the field and the charge of the ions. During World War II, calutrons were developed to use this principle to obtain substantial quantities of high-purity uranium-235, by taking advantage of the small mass difference between uranium isotopes. (Full article...)Did you know -
- ...that while Albert Einstein is most famous for his Theory of Relativity, he was awarded the Nobel Prize for his explanation of the photoelectric effect?
- ...that gravitational tidal accelerations are the result of the curvature of spacetime?
- ...that the blue glow of the Cherenkov effect is due to electrons moving faster than the speed of light in water?
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Difference between classical and modern physics
While physics aims to discover universal laws, its theories lie in explicit domains of applicability. Loosely speaking, the laws of classical physics accurately describe systems whose important length scales are greater than the atomic scale and whose motions are much slower than the speed of light. Outside of this domain, observations do not match their predictions. Albert Einstein contributed the framework of special relativity, which replaced notions of absolute time and space with spacetime and allowed an accurate description of systems whose components have speeds approaching the speed of light. Max Planck, Erwin Schrödinger, and others introduced quantum mechanics, a probabilistic notion of particles and interactions that allowed an accurate description of atomic and subatomic scales. Later, quantum field theory unified quantum mechanics and special relativity. General relativity allowed for a dynamical, curved spacetime, with which highly massive systems and the large-scale structure of the universe can be well-described. General relativity has not yet been unified with the other fundamental descriptions; several candidate theories of quantum gravity are being developed.
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July anniversaries
- July 1654 – Blaise Pascal's letters to Pierre de Fermat on the "Problem of Points"
- July 1820 – Hans Christian Ørsted published pamphlet about the relation between electricity and magnetism
- July 1849 – Fizeau publishes results of speed of light experiment.
- July 1914 – AT&T tested the first working transcontinental telephone line when the president of the company spoke from one coast to the other. Months later Alexander Graham Bell repeated his famous statement over the phone in New York City which was heard by Dr. Watson in San Francisco.
- July 1957 – John Bardeen, Leon Cooper and Robert Schrieffer submit detailed research report, "Theory of Superconductivity" to the Physical Review (it was published in December).
- July 1994 – Comet Shoemaker–Levy 9 collides with Jupiter.
- 16 July 1945 – Trinity test, named by J. Robert Oppenheimer.
- 16 July 1969 – Apollo 11 launched.
- 20 July 1969 – Apollo 11 landed on the Moon.
- 23 July 1995 – Comet Hale-Bopp discovered.
- 2 July 1876 - Harriet Brooks was born; noted for research in nuclear transmutations and for discovering the Atomic recoil.
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Classical physics traditionally includes the fields of mechanics, optics, electricity, magnetism, acoustics and thermodynamics. The term Modern physics is normally used for fields which rely heavily on quantum theory, including quantum mechanics, atomic physics, nuclear physics, particle physics and condensed matter physics. General and special relativity are usually considered to be part of modern physics as well.
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