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Gravity assist

A gravitational slingshot, gravity assist maneuver or swing-by is the use of the relative movement and gravity of a planet to alter the path and speed of a spacecraft, typically in order to save fuel, time, and expense. Gravity assistance can be ...

                                               

Ground state

Ground state is the lowest level of energy in a particle, atom or molecule. If energy is added from outside, then the level of energy is increased, and the ground state is changed. Changing ground state is the process of excitement of electrons t ...

                                               

Hardness

Hardness is a measure of how much a material resists changes in shape. Hard things resist pressure. Some examples of hard materials are diamond, boron carbide, quartz, tempered steel, ice, granite, concrete. Ability of material to resist wear, te ...

                                               

Hydrogen atom

A hydrogen atom is an atom of the chemical element hydrogen. Its parts are a single negatively-charged electron that circles a single positively-charged nucleus of the hydrogen atom. The nucleus of hydrogen consists of only a single proton in the ...

                                               

Inflation (cosmology)

In physical cosmology, the idea of inflation is a proposed theory that would explain many features of the present-day universe, including the existence of large-scale structures such as galaxies. The theory was proposed by Alan Guth in the 1970s.

                                               

Island of stability

The chemical elements beyond lead are radioactive, and they do not have stable isotopes. This means that they will decay into other elements. Except for Plutonium, their half life is in the order of several minutes, to seconds. There is a theory ...

                                               

Lift Coefficient

The lift coefficient is coefficient without a dimension that relates the lift generated by an airfoil, the dynamic pressure of the fluid flow around the airfoil, and the planform area of the airfoil. It may also be described as the ratio of lift ...

                                               

LIGO

The Laser Interferometer Gravitational-Wave Observatory is a large-scale physics observatory which detects cosmic gravitational waves co-founded by Scottish physicist Ronald Drever. They were first funded by the National Science Foundation and we ...

                                               

Liquid scintillation counting

Liquid scintillation counting is an analytical technique. It is used to measure radiation from beta - emitting nuclides. It can also detect the auger electrons emitted from Chromium-51 and Iodine-125 samples. Samples of nuclides are dissolved or ...

                                               

Locating (physics)

The act of locating something, of finding or defining the location of something, is a basic idea of modern science. In physics to say what "to locate" or "location" means, we must explain with clear talk how we do the job of locating something. F ...

                                               

Magnetic levitation

Magnetic levitation, maglev, or magnetic suspension is a method by which an object is suspended with no support other than magnetic fields. Magnetic force is used to counteract the effects of the gravitational acceleration and any other accelerat ...

                                               

Magnetic pendulum

A magnetic pendulum is an experiment where a metal ball on a thread can be influenced by a number of magnets on the ground. The length of the rope is such that the ball cannot touch the magnets, but is still influenced by them. If the ball is mov ...

                                               

Majorana fermion

A Majorana fermion, also referred to as a Majorana particle, is a fermion that has the same properties as its antiparticle. Ettore Majorana, an Italian physicist, thought they would exist, in 1937. Majorana disappeared in 1938, and the particles ...

                                               

Mass versus weight

In the physical sciences, mass and weight are different. The mass of an object is a measure of the amount of matter in the object. Weight is a measure of the force on the object caused by a gravitational field. In other words, weight is how hard ...

                                               

Metastability

Metastability has slightly different meanings in different fields of knowledge. The general idea, however, is that something is metastable if it is not changing, yet given a small force it will transition to another, more stable state. For exampl ...

                                               

Mie scattering

Mie scattering is the way that light scatters when it hits an object. It is named after the German physicist, Gustav Mie. This theory is good for all wavelengths of light, and all object sizes. If the object is much smaller than the wavelength of ...

                                               

Molecular orbital

In chemistry, a molecular orbital explains what happens to electrons when atoms join together in a molecule. A MO is a mathematical function which describes the wave-like behaviour of an electron in a molecule. The functions can tell the probabil ...

                                               

Multiverse

A multiverse is the theory of a conjectured set of multiple possible universes, including ours, which make up reality. These universes are sometimes called parallel universes. A number of different versions have been considered. The term "multive ...

                                               

Natural units

Natural units are ways of measuring things that depend on some basic characteristics of nature that do not change. Which of these basic quantities to choose can depend on the physics problems being investigated, and sometimes choosing one thing a ...

                                               

Particle detector

A particle detector, also known as a radiation detector, is a device used to detect, track, and/or identify high-energy particles. These particles can be made by nuclear decay, cosmic radiation, or reactions in a particle accelerator. Particle de ...

                                               

Phase

A phase is one part of a cycle or change that goes in a circle. For example, the moon has phases. The seasons of the year, spring, summer, fall, and winter, are also phases. The planet Venus has phases, like the moon: Galileo showed that the phas ...

                                               

Phonon

In physics, a phonon is a quantized lattice vibration. The word quantized is used in physics to mean that only certain values of something are allowed. Something that is quantized can be thought of as stairs; you can only move from step to step a ...

                                               

Photoelectric effect

The photoelectric effect is a phenomenon in physics. The effect is based on the idea that electromagnetic radiation is made of a series of particles called photons. When a photon hits an electron on a metal surface, the electron can be emitted. T ...

                                               

Planck constant

The Planck constant says how much the energy of a photon increases, when the frequency of its electromagnetic wave increases by 1. It is named after the physicist Max Planck. The Planck constant is a fundamental physical constant. It is written a ...

                                               

Plasma window

A Plasma window is a field of plasma that fills an area of space. It is similar to a force field. The area is created by using magnetism to hold the plasma in place. With current technology, this area of space is quite small. It is in the shape o ...

                                               

Poissons ratio

Poissons ratio is a measure of the contraction that happens when an object is stretched. This contraction is perpendicular to the stretching force. It can also expand as the object is compressed in a perpendicular direction. For example, if a blo ...

                                               

Polarity

In physics, polarity describes an attribute that can usually have two values: A magnet has a polarity, in that one end is the "north" and the other is the "south". Polarized light has waves which all line up in the same direction. The spin of an ...

                                               

Pressure in liquids

Fluid pressure is a measurement of the force per unit area. Fluid pressure can be caused by gravity, acceleration, or forces in a closed container. Since a fluid has no definite shape, its pressure applies in all directions. Fluid pressure can al ...

                                               

Quantum gravity

Quantum gravity is an area of research in physics. Right now, physics is able to describe gravity of real-life sized objects using general relativity. Physicists can also describe the universe on a microscopic scale with quantum mechanics. The go ...

                                               

Radioactive contamination

Radioactive contamination or radiological contamination is the contamination of the environment with radioactive materials, where these materials are not present. Many radioactive substances have very long half lives; this means that if they are ...

                                               

Resonance

In physics, resonance is the tendency of a system to vibrate with increasing amplitudes at some frequencies of excitation. These are known as the systems resonant frequencies. The resonator may have a fundamental frequency and any number of harmo ...

                                               

Rigidly rotating disk paradox

In theoretical physics, a branch of physics, the rigidly rotating disk paradox, sometimes called the Ehrenfest paradox, is a paradox concerning a rotating disk. Basically, the paradox says that when a disk is rotated, it will have a smaller circu ...

                                               

Shapiro delay

The Shapiro time delay is a physics experiment. It is one of the four classic solar system observations or experiments which test general relativity. Radar signals passing near a massive object take slightly longer to travel to a target and longe ...

                                               

Simple harmonic motion

A thing that is moving back and forth or to and fro is said to be vibrating. Another word for vibration is oscillation. A special way of vibrating or oscillating is called simple harmonic motion. When measuring motion, it is normal to make a grap ...

                                               

Skyrmion

A skyrmion is an quantum entity in atomic physics that can occur in some materials like solids and Bose–Einstein condensates. They are made up from a persistent vortex that is a quantum superposition of baryons and resonance states. These vortice ...

                                               

Sorption

When two chemical substances come in contact with each other, through what is called a phase, they will interact with each other in that phase. They may also have an interface. If a substance accumulates within a phase this is called absorption, ...

                                               

Specific gravity

Specific Gravity is a special case of relative density. It is defined as the ratio of the density of a given substance, to the density of water H 2 O. Substances with a specific gravity greater than 1 are heavier than water, and those with a spec ...

                                               

Substance

Substance is the material, or matter, of which something is made. Substances are physical things that can be seen, touched, or measured. They are made up of one or more elemental parts. Iron, aluminium, water and air are examples of substances.

                                               

Superfluidity

Superfluidity is a state of matter where a liquid can act very strangely. Some of the things a superfluid can do are: It stays still when its container is spun, instead of starting a whirlpool like when a sink full of water is drained. However, a ...

                                               

Synchrotron

A synchrotron is a type of particle accelerator where particles travel around many times in a circle. It uses a magnetic field to turn the particles in the circle and an electric field to speed up the particles. The components are carefully match ...

                                               

Thixotropy

Thixotropy is the property of certain gels or fluids that are viscous under normal conditions, but flow when shaken, agitated, or otherwise stressed. In more technical language: some Non-Newtonian fluids show a change in viscosity; the longer the ...

                                               

Time travel

Time travel is the idea of going back in time to the past or forward to the future. We always travel forward, to the future. Time travel to the past is not known to be possible, but it is much used in fiction. The Time Machine by H. G. Wells was ...

                                               

World line

A world line is the unique path that an object has as it travels through both space and time, usually called spacetime. As we learn from special relativity, the faster an object goes, the more time slows down for that object. As you can see in th ...

                                               

Young–Laplace equation

In physics, the Young–Laplace equation is a nonlinear partial differential equation that describes the capillary pressure difference across the interface between two static fluids, such as water and air. This difference is due to the phenomenon o ...

                                               

Zero-point energy

Zero-point energy is the energy of the vacuum space, the space between the subatomic particles within atoms. There are a few theories about how much energy there is in that space. There is the theory that there is an incredibly small, very near-z ...

                                               

List of astronomers

Zu Chongzhi, 425 – 500 Zhang Heng 78 – 139 Fritz Zwicky L. V. Zhuravleva Russia, Ukraine Zhang Yuzhe China, 1902 – 1986 Zhang Daqing China, 1969 – Yakov Borisovich Zeldovich USSR, 1914 – 1987 Other scientists whose work had an impact on astronomy ...

                                               

Glossary of astronomy

Accretion disk - An accretion disk or disc is an astronomical term. It describes a disc of material being drawn in by gravity to a centre of mass, such as a star or black hole. As the material comes in, it spins round the central body and radiate ...

                                               

List of telescope types

Astronomical telescopes are divided into subgroups. All telescopes work by collecting electromagnetic radiation and focussing it into an image which may be seen or photographed. The purpose is to see things which are far away in the universe. The ...

                                               

List of biochemistry topics

abiogenesis - adenine - adenosine diphosphate ADP - adenosine triphosphate ATP - albumin - allotrope - alpha helix - amino acid - amylase - antibiotic - antibody - antigen -

                                               

List of chemistry topics

Acid - adenosine diphosphate ADP - adenosine triphosphate ATP - alcohol - alkali - alkali metal - alkaline earth metal - allotrope - Alpha helix - amino acid - antibiotic - antibody - apoptosis - archaea - atom - atomic mass - atomic mass unit - ...