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- The scope of physics
- The study of heat, thermodynamics, and statistical mechanics
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- The Journal of Chemical Physics, 149, 034101 (2018). DeePMD-kit: A deep learning package for many-body potential energy representation and molecular dynamics, Han Wang, Linfeng Zhang, Jiequn Han, Weinan E, Computer Physics Communications, 228, 178-184 (2018).
- Welcome to the Physics Learning Site! This site was created by Jacob Filipp, shile studying in Toronto, Canada, to teach grade 12 kinematics ( motion ) concepts. These are the sections of the Physics Learning Site: The Basics A short explanation of Basic motion concepts.
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Join Britannica's Publishing Partner Program and our community of experts to gain a global audience for your work!Physics, science that deals with the structure of matter and the interactions between the fundamental constituents of the observable universe. In the broadest sense, physics (from the Greek physikos) is concerned with all aspects of nature on both the macroscopic and submicroscopic levels. Its scope of study encompasses not only the behaviour of objects under the action of given forces but also the nature and origin of gravitational, electromagnetic, and nuclear force fields. Its ultimate objective is the formulation of a few comprehensive principles that bring together and explain all such disparate phenomena.
What is physics?
Physics is the branch of science that deals with the structure of matter and how the fundamental constituents of the universe interact. It studies objects ranging from the very small using quantum mechanics to the entire universe using general relativity.
Why does physics work in SI units?
Physicists and other scientists use the International System of Units (SI) in their work because they wish to use a system that is agreed upon by scientists worldwide. Since 2019 the SI units have been defined in terms of fundamental physical constants, which means that scientists anywhere using SI can agree upon the units they use to measure physical phenomena.
Physics is the basic physical science. Until rather recent times physics and natural philosophy were used interchangeably for the science whose aim is the discovery and formulation of the fundamental laws of nature. As the modern sciences developed and became increasingly specialized, physics came to denote that part of physical science not included in astronomy, chemistry, geology, and engineering. Physics plays an important role in all the natural sciences, however, and all such fields have branches in which physical laws and measurements receive special emphasis, bearing such names as astrophysics, geophysics, biophysics, and even psychophysics. Physics can, at base, be defined as the science of matter, motion, and energy. Its laws are typically expressed with economy and precision in the language of mathematics.
Both experiment, the observation of phenomena under conditions that are controlled as precisely as possible, and theory, the formulation of a unified conceptual framework, play essential and complementary roles in the advancement of physics. Physical experiments result in measurements, which are compared with the outcome predicted by theory. A theory that reliably predicts the results of experiments to which it is applicable is said to embody a law of physics. However, a law is always subject to modification, replacement, or restriction to a more limited domain, if a later experiment makes it necessary.
The ultimate aim of physics is to find a unified set of laws governing matter, motion, and energy at small (microscopic) subatomic distances, at the human (macroscopic) scale of everyday life, and out to the largest distances (e.g., those on the extragalactic scale). This ambitious goal has been realized to a notable extent. Although a completely unified theory of physical phenomena has not yet been achieved (and possibly never will be), a remarkably small set of fundamental physical laws appears able to account for all known phenomena. The body of physics developed up to about the turn of the 20th century, known as classical physics, can largely account for the motions of macroscopic objects that move slowly with respect to the speed of light and for such phenomena as heat, sound, electricity, magnetism, and light. The modern developments of relativity and quantum mechanics modify these laws insofar as they apply to higher speeds, very massive objects, and to the tiny elementary constituents of matter, such as electrons, protons, and neutrons.
The scope of physics
The traditionally organized branches or fields of classical and modern physics are delineated below.
Mechanics
Mechanics is generally taken to mean the study of the motion of objects (or their lack of motion) under the action of given forces. Classical mechanics is sometimes considered a branch of applied mathematics. It consists of kinematics, the description of motion, and dynamics, the study of the action of forces in producing either motion or static equilibrium (the latter constituting the science of statics). The 20th-century subjects of quantum mechanics, crucial to treating the structure of matter, subatomic particles, superfluidity, superconductivity, neutron stars, and other major phenomena, and relativistic mechanics, important when speeds approach that of light, are forms of mechanics that will be discussed later in this section.
In classical mechanics the laws are initially formulated for point particles in which the dimensions, shapes, and other intrinsic properties of bodies are ignored. Thus in the first approximation even objects as large as Earth and the Sun are treated as pointlike—e.g., in calculating planetary orbital motion. In rigid-body dynamics, the extension of bodies and their mass distributions are considered as well, but they are imagined to be incapable of deformation. The mechanics of deformable solids is elasticity; hydrostatics and hydrodynamics treat, respectively, fluids at rest and in motion.
The three laws of motion set forth by Isaac Newton form the foundation of classical mechanics, together with the recognition that forces are directed quantities (vectors) and combine accordingly. The first law, also called the law of inertia, states that, unless acted upon by an external force, an object at rest remains at rest, or if in motion, it continues to move in a straight line with constant speed. Uniform motion therefore does not require a cause. Accordingly, mechanics concentrates not on motion as such but on the change in the state of motion of an object that results from the net force acting upon it. Newton’s second law equates the net force on an object to the rate of change of its momentum, the latter being the product of the mass of a body and its velocity. Newton’s third law, that of action and reaction, states that when two particles interact, the forces each exerts on the other are equal in magnitude and opposite in direction. Taken together, these mechanical laws in principle permit the determination of the future motions of a set of particles, providing their state of motion is known at some instant, as well as the forces that act between them and upon them from the outside. From this deterministic character of the laws of classical mechanics, profound (and probably incorrect) philosophical conclusions have been drawn in the past and even applied to human history.
Lying at the most basic level of physics, the laws of mechanics are characterized by certain symmetry properties, as exemplified in the aforementioned symmetry between action and reaction forces. Other symmetries, such as the invariance (i.e., unchanging form) of the laws under reflections and rotations carried out in space, reversal of time, or transformation to a different part of space or to a different epoch of time, are present both in classical mechanics and in relativistic mechanics, and with certain restrictions, also in quantum mechanics. The symmetry properties of the theory can be shown to have as mathematical consequences basic principles known as conservation laws, which assert the constancy in time of the values of certain physical quantities under prescribed conditions. The conserved quantities are the most important ones in physics; included among them are mass and energy (in relativity theory, mass and energy are equivalent and are conserved together), momentum, angular momentum, and electric charge.
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Associate professor of physics shares the honor with colleague Phillip Mocz for their novel dark matter research.
Kelso Harper | MIT Kavli Institute for Astrophysics and Space Research
January 14, 2021
Mark Vogelsberger, an associate professor of physics at MIT, has received the 2020 Buchalter Cosmology Prize in a collaboration led by Phillip Mocz, a postdoc at Princeton University. Their research presents a novel simulation of the early universe with a theorized ultralight, or “fuzzy,” dark matter particle. The Buchalter Prize awarded the researchers Third Prize and $2,500 for their boundary-pushing work in cosmology.
Most astrophysicists agree that a theorized substance called dark matter makes up 84 percent of the mass of the universe. Scientists can observe the gravitational effects of this matter on the visible universe, but they have yet to detect a dark matter particle. The prevailing theory of “cold” dark matter suggests a slower-moving particle with roughly 100,000 times the mass of an electron. But because such a particle remains elusive, researchers are considering other theorized particles, like slightly lighter “warm” dark matter and ultralight “fuzzy” dark matter, which has about one-octillionth (10-27) the mass of an electron.
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Depending on the type of dark matter, the early universe would have taken shape in very different ways. Vogelsberger and his colleagues created three simulations of early galaxy formation in scenarios with cold, warm, and fuzzy dark matter particles. In the cold dark matter simulation, galaxies formed in dense clumps. Conversely, the warm and fuzzy simulations showed long, tail-like filaments of galaxy formation. Unique to the fuzzy dark matter simulation, however, are striated bands of formation, like the strings on a harp. This happens because the fuzzy particles are so incredibly light that they act more like waves than individual particles. When these waves interact, they either reinforce each other or cancel out, producing quantum interference patterns on a cosmic scale.
Physics Ch.11lightmr.'s Learning Website -
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