This physics dictionary provides useful terms in exploring the subject, where sometimes a common word can have a very specific interpretation. Learning the proper terms can help you focus your time on learning the more complex aspects of physics.
Absolute zero is the lowest possible temperature, at which point the atoms of a substance transmit no thermal energy - they are completely at rest. It is 0 degrees on the Kelvin scale, which translates to -273.15 degrees Celsius (or -459.67 degrees Fahrenheit). The concept of an absolute cold was first presented by Robert Boyle in his 1665 New Experiments and Observations touching Cold. Various physicists explored this phenomenon, until Lord Kelvin derived his thermodynamic temperature scale, extrapolating backward to absolute zero based purely on the laws of thermodynamics. Some substances, when cooled to near-absolute zero temperatures, reach a state of matter known as a superfluid, which exhibit strange properties.
Acceleration is the rate of change of velocity as a function of time. It is vector. In calculus terms, acceleration is the second derivative of position with respect to time or, alternately, the first derivative of the velocity with respect to time. The SI units for acceleration are m / s2 (meters per second squared or meters per second per second).
An adiabatic process is a thermodynamic process in which there is no heat transfer (Q) into or out of the system. In other words Q = 0. An adiabatic process is generally obtained by surrounding the entire system with a strongly insulating material or by carrying out the process so quickly that there is no time for a significant heat transfer to take place. Applying the first law of thermodynamics to an adiabatic process, we obtain
Biophysics is the application of physics to biological systems. This interdisciplinary field is quickly growing in the modern scientific community.
A Bose-Einstein condensate is a rare state (or phase) of matter in which a large percentage of bosons collapse into their lowest quantum state, allowing quantum effects to be observed on a macroscopic scale. The bosons collapse into this state in circumstances of extremely low temperature, near the value of absolute zero. Satyendra Nath Bose developed statistical methods, later utilized by Albert Einstein, to describe the behavior of massless photons and massive atoms, as well as other bosons. This Bose-Einstein statistics described the behavior of a Bose gas composed of uniform particles of integer spin (i.e. bosons). When cooled to extremely low temperatures, Bose-Einstein statistics predicts that the particles in a Bose gas will collapse into their lowest accessible quantum state, creating a new form of matter, which is called a superfluid. This is a specific form of condensation which has special properties. Bose-Einstein condensates were a purely theoretical conjecture until experimentally observed by Eric Cornell and Carl Wieman at the University of Colorado at Boulder in 1995, for which they received the 2001 Nobel prize.
A Definition: A bottom quark (symbol b) is a third generation quark with the following properties
Buoyancy is the phenomenon (discovered by Archimedes) that an object less dense than a fluid will float in the fluid. More generally, Archimedes' principle states that a fluid will exert an upward force on an object immersed in it equal to the weight of the fluid displaced by the object.
A cathode ray is a beam of electrons that travel from the negatively charged to positively charged end of a vacuum tube, across a voltage difference between the electrodes placed at each end. The electrode at the negative end is called a cathode; the electrode at the positive end is called an anode. Since electrons are repelled by the negative charge, the cathode is seen as the source of the cathode ray in the vacuum chamber.
With the 1650 invention of the vacuum pump, scientists were able to study the effects of different material in vacuums, and a more complete study of electricity soon followed. It was recorded as early as 1705 that in vacuums (or near vacuums) electrical discharges could travel a larger distance.
Such phenomena became popular as novelties, and even reputable physicists such as Michael Faraday studied the effects of them. In the late 1800s, physicist Phillip von Lenard studied the cathode rays intently and his work earned him the 1905 Nobel Prize in Physics. The most popular commercial application of cathode ray technology is in the form of traditional television sets.
A charm quark (symbol c) is a second generation quark with the following properties
A cloud chamber is a sealed container of water vapor that has been supercooled and supersaturated. When a charged particle enters the chamber, it ionizes the vapor, causing it to condense within the chamber leaving a visible trail. Observation of the properties of these trails can provide information about the type of particle that caused them.
The cloud chamber was invented by Charles Thomson Rees Wilson, based on observations that came out of his meteorological studies of clouds. The first cloud chamber was built in 1911, for which Wilson received the 1927 Nobel Prize in Physics.
An electronic device with a multiple inputs and a single output. The output signal is only transmitted when signals are received at all of the inputs. The concept of the method of coincidence was developed by German physicist Walther Bothe in 1929, for which he received the 1954 Nobel Prize in Physics. Bruno Rossi invented the first electronic coincidence circuit in 1930.
Among other areas, coincidence circuits are widely used in particle physics, such as detecting cosmic rays.
Condensation is the process by which matter transitions from a gas (or vapor) phase into a liquid phase. Dew forming on grass in the morning is a common example of condensation.
Cosmic Microwave Background (CMB) radiation is the name for the remnant energy left over from the formation of the universe, according to the Big Bang theory.
The CMB was first proposed in 1948 by Big Bang supporter George Gamow and his colleagues (although previous flawed estimates of space's temperature had already been calculated). In 1964, a research team at Princeton began building a Dicke radiometer in an attempt to detect the CMB, but they were beaten to it by an accidental finding by Arno Penzias and Robert Woodrow Wilson of Bell Telephone Laboratories. They detected a 3.5 K temperature with their equipment which could not be accounted for, until they learned of the CMB and realized what they'd detected. This discovery essentially ushered in the end of the steady state theory, which would allow for a universe with no beginning and earned Penzias and Wilson the 1978 Nobel Prize in Physics.
Over the years, various projects have re-measured the CMB with greater accuracy, such as the WMAP project which detected minute variations in this temperature throughout the universe.
Electrical current is a measure of the amount of electrical charge transferred per unit time. It represents the flow of electrons through a conductive material. Current is a scalar quantity (though in circuit analysis, the direction of current is relevant). The SI unit of electrical current is the ampere, defined as 1 coulomb/second.
Dark energy is a hypothetical form of energy that permeates space and exerts a negative pressure, which would have gravitational effects to account for the differences between the theoretical and observational results of gravitational effects on visible matter. Dark energy is not observed, but rather inferred, along with dark matter, as a probable explanation for these effects. The term dark energy was coined by the theoretical cosmologist Michael S. Turner.
Dark matter is a hypothesized form of matter particle that does not reflect or emit electromagnetic radiation. The existence of dark matter is inferred from gravitational effects on visible matter, such as stars and galaxies. A small percentage of the gravitational effects observed
A small percentage of the gravitational effects observed are from visible matter (some estimates are as low as 4% of total gravitational effects). The remaining 96% is presumed to result from dark matter or dark energy, though these terms are somewhat indicative of our ignorance of the exact nature of these unknown quantities, as they have never been directly observed.
The density of a material is the mass per unit volume.
A down quark (symbol d) is a first generation quark with the following properties:
Electrical current is a measure of the amount of electrical charge transferred per unit time. It represents the flow of electrons through a conductive material. Current is a scalar quantity (though in circuit analysis, the direction of current is relevant). The SI unit of electrical current is the ampere, defined as 1 coulomb/second.
Voltage is a representation of the electric potential energy per unit charge. If a unit of electrical charge were placed in a location, the voltage indicates the potential energy of it at that point. In other words, it is a measurement of the energy contained within an electric field, or an electric circuit, at a given point. Voltage is a scalar quantity. The SI unit of voltage is the volt, such that 1 volt = 1 joule/coulomb.
An electron is a fundamental particle, which means it cannot be broken into smaller particles. Electrons may be bound in the electron cloud surrounding an atomic nucleus, or may break free from the cloud as a free electron.
Electron Details
The electron is a fermion, which means it has a half-integer spin. It is a member the lepton family of particles. The antiparticle of the electron is called the positron.
Discovery of the Electron In 1974, G. Johnstone Stoney theorized the existence of a unit of charge. He coined the term electron to describe such a unit charge in 1894. The electron was not discovered until 1897, when J.J. Thomson discovered the particle in his research with cathode ray tubes. It was not until 1909 when experimental physicist Robert Millikan calculated it in his classic oil-drop experiment.
Entropy is the quantitative measure of disorder in a system. The concept comes out of thermodynamics, which deals with the transfer of heat energy within a system. Instead of talking about some form of absolute entropy, physicists generally talk about the change in entropy that takes place in a specific thermodynamic process.
Calculating Entropy In an isothermal process, the change in entropy (delta-S) is the change in heat (Q) divided by the absolute temperature
(T)delta-S = Q/TIn any reversible thermodynamic process, it can be represented in calculus as the integral from a processes initial state to final state of dQ/T.
The SI units of entropy are J/K (joules/degrees Kelvin).
Entropy and The Second Law of Thermodynamics One way of stating the second law of thermodynamics is: In any closed system, the entropy of the system will either remain constant or increase.One way to view this is that adding heat to a system causes the molecules and atoms .It may be possible (though tricky) to reverse the process in a closed system (i.e. without drawing any energy from or releasing energy somewhere else) to reach the initial state, but you can never get the entire system less energetic than it started ... the energy just doesn't have anyplace to go. Misconceptions about Entropy .This view of the second law of thermodynamics is very popular, and it has been misused. Some argue that the second law of thermodynamics means that a system can never become more orderly. Not true. It just means that in order to become more orderly (for entropy to decrease), you must transfer energy from somewhere outside the system, such as when a pregnant woman draws energy from food to cause the fertilized egg to become a complete baby, completely in line with the second line's provisions. Also Known As: Disorder, Chaos, Randomness (all three imprecise synonyms)
Force is a quantitative description of the interaction between two physical bodies, such as an object and its environment. Force is proportional to acceleration. In calculus terms, force is the derivative of momentum with respect to time. Contact force is defined as the force exerted when two physical objects come in direct contact with each other. Other forces, such as gravitation and electromagnetic forces, can exert themselves even across the empty vacuum of space. The concept of force was originally defined by Sir Isaac Newton in his three laws of motion. Force is a vector. The SI unit for force is the newton (N). One newton is equal to 1 kg * m/s2.
A graviton is a theoretical virtual particle which would mediate the force of gravity. It is proposed by various theories of quantum gravity. The graviton would support a quantum representation of gravity which would consolidate it with the other fundamental forces of physics, which are also mediated by virtual particles. Gravitons have not been experimentally observed. The theoretical models that include them predict a massless particle of spin 2, which would make it a boson.
Heat energy (or just heat) is a form of energy which transfers among particles in a substance (or system) by means of kinetic energy of those particle. In other words, under kinetic theory, the heat is transfered by particles bouncing into each other. In physical equations, the amount of heat transferred is usually denoted with the symbol Q.
Heat vs. Temperature Note this crucial component to the above definition: Heat always refers to the transfer of energy between systems (or bodies), not to energy contained within the systems (or bodies).This can be very confusing, because we're used to in day-to-day conversation talking about heat as if it's contained in something. This distinction between heat and temperature is subtle, but very important.
Example The iron is hot, so it's reasonable to say it must have a lot of heat in it.Reasonable, but wrong. It's more appropriate to say that it has a lot of energy in it (i.e. it has a high temperature), and touching it will cause that energy to transfer to your hand ... in the form of heat.
Units of Heat , As a form of energy, the SI unit for heat is the joule (J), though heat is frequently also measured in the calorie (cal), which is defined as the amount of heat required to raise the temperature of one gram of water from 14.5 degrees Celsius to 15.5 degrees Celsius. Heat is also sometimes measured in British thermal units or Btu.
Also Known As: thermal energy
The Higgs boson is a theoretical particle that is part of the Standard Model of quantum physics. In the Standard Model, space consists of the Higgs field, with a non-zero value in all space. There are two neutral and two charged components to the field. One of the neutral and both of the charged components combine to create the W and Z bosons, which create the weak force, one of the fundamental forces of physics. The remaining neutral charge creates the scalar Higgs boson, which has neither charge nor spin (thus causing it to follow Bose-Einstein statistics). This is crucial in using the Standard Model to explain where mass comes from. As of the time of writing (January 2007), the Higgs boson is the only Standard Model particle has not been observed experimentally.
Recent findings on the mass of the W boson, however, have helped narrow down the energy levels at which it would exist. The current bounds of the Higgs boson predict that it will have a mass somewhere between 114 GeV and 153 GeV. The Higgs boson was first theorized in 1964 by the British physicist Peter Higgs, who expanded on the ideas of American theoretical physicist Phillip Anderson.
Impulse is defined as a force multiplied by the amount of time it acts over. In calculus terms, the impulse can be calculated as the integral of force with respect to time. Alternately, impulse can be calculated as the difference in momentum between two given instances. The SI units of impulse are N*s or kg*m/s.
Inertia is the name for the tendency of an object in motion to remain in motion, or an object at rest to remain at rest, unless acted upon by a force. This concept was quantified in Newton's First Law of Motion.
An atom or group of atoms that carry a positive or negative electrical charge as a result of gaining or losing electrons.
An isobaric process is a thermodynamic process in which the pressure remains constant. This is usually obtained by allowed the volume to expand or contract in such a way to neutralize any pressure changes that would be caused by heat transfer. In an isobaric process, there are typically internal energy changes, work is done by the system, and heat is transferred, so none of the quantities in the first law of thermodynamics readily reduce to zero. However, the work at a constant pressure can be fairly easily calculated with the equation
Since W is the work, p is the pressure (always positive) and delta-V is the change in volume, we can see that there are two possible outcomes to an isobaric process
Isobaric Process and Phase Diagrams . In a phase diagram, an isobaric process would show up as a horizontal line, since it takes place along a constant pressure.
An isochoric process is a thermodynamic process in which the volume remains constant. Since the volume is constant, the system does no work and W = 0. This is perhaps the easiest of the thermodynamic variables to control, since it can be obtained by placing the system in a sealed container which neither expands nor contracts. Applying the first law of thermodynamics to this situation, we find that: delta-U = Q Since delta-U is the change in internal energy and Q is the heat transfer into or out of the system, we see that all of the heat either comes from internal energy or goes into increasing the internal energy.
Constant Volume, But W is Non-zeroIt is actually possible to do work on a system without changing the volume, as in the case of stirring a liquid. Some sources use isochoric in these cases to mean zero-work regardless of whether there is a change in volume or not. In most straightforward applications, however, this nuance will not need to be considered ... if the volume remains constant throughout the process, it is an isochoric process
An isothermal process is a thermodynamic process in which the temperature of the system remains constant. The heat transfer into or out of the system typically must happen at such a slow rate that the thermal equilibrium is maintained.
Other Factors in an Isothermal ProcessIn general, during an isothermal process there is a change in internal energy, heat energy, and work. The internal energy of an ideal gas, however, depends solely on the temperature, so the change in internal energy during an isothermal process for an ideal gas is also 0.
Isothermal Processes and States of Matter In a phase diagram, an isothermal process is indicated by following a vertical line (or plane, in a 3D phase diagram) along a constant temperature. Therefore, if the pressure and volume change, it is possible for a substance to change its state of matter even while its temperature remains constant, if you're careful about how you apply or remove heat from the system.
Mass is the quantity of inertia possessed by an object or the proportion between force and acceleration referred to in Newton's Second Law of Motion.
This is not a very good operational definition of mass, of course. In most common instances, mass is determined by weighing the object and using the force of gravity to calculate the value automatically - which is why you can get on a scale and have read your mass.
The SI unit of mass is the kilogram (kg).Because of the relationship between weight and mass, these concepts are frequently confused. You can, in fact, convert exactly between weight and mass on the Earth's surface. This confusion is heightened by the fact that in much of metric world, weight is not dealt with, and mass is used in its place almost exclusively. The main difference is that if you were to leave the Earth and go to the Moon, your weight would change but your mass would remain constant.
Matter has many definitions, but the most common is that it is any substance which has mass and occupies space. All physical objects are composed of matter, in the form of atoms, which are in turn composed of protons, neutrons, and electrons. Photons have no mass, so they are an example of something in physics is not comprised of matter. They are also not considered objects in the traditional sense, as they cannot exist in a stationary state.
Phases of MatterMatter can exist in various phases: solid, liquid, gas, or plasma. Most substances can transition between these phases based on the amount of heat the material absorbs (or loses).
Momentum is the product of an object's mass and velocity. It is a vector. The SI units of momentum are kg * m/s.
technology is the understanding and control of matter at the realm of 1 to 100 nanometers. (For reference, a piece of paper is about 100,000 nanometers thick.) At the nanoscale, matter functions differently from both the individual atomic and macroscopic scales, so some unique properties are available for use in the field.
Development of Nanotechnology Nanotechnology is a natural end-result of scientific development and our ability to understand and manipulate matter at smaller and smaller levels. Just as computers have gone from bulky, room-filling monstrosities to handheld computers, such reductions in size will continue until we reach fundamental physical limits.
Feynman and NanotechnologyOn December 29, 1959, the influential American physicist Richard P. Feynman presented a talk to the American Physical Society entitled There's Plenty of Room at the Bottom: An Invitation to Enter a New Field of Physics. Among physicists, this is respectfully called the classic talk (it's the first hit on a Google search of classic talk). He asked Why cannot we write the entire 24 volumes of the Encyclopedia Brittanica on the head of a pin? and introduced the concept of nanotechnology.
Spread of NanotechnologyThough Feynman's speech inspired many researchers, it wasn't until the mid-1980s that nanotechnology began to seep into the cultural mainstream conversation. In 1986, the MIT researcher K. Eric Drexler wrote Engines of Creation which laid out extensive prospects of emerging nanotechnology research.
Nanotechnology and MedicineOne major application of nanotechnology is in the field of medicine, and in fact the knowledge gained from research of natural nanomachines, such as bacteria, has proven essential to the field. In this respect, it has developed some close connections with biophysics. It is theorized that man-made nanomachines could repair damage to the human body that is currently untreatable.
Preparing for a Career in NanotechnologyThere are few degrees of study specifically in nanotechnology, so look for a good, well-rounded physics program. Nanotechnology works at tiny levels of matter, so knowledge of atomic, molecular, chemical and quantum physics is essential to this field of study. Working knowledge of biochemistry, chemistry, and biophysics, as well as a proficiency with complex mathematics, would also help qualify you for this field.
Nuclear fission is a nuclear reaction in which a heavy nucleus (such as uranium) splits into two lighter nuclei (and possible some other radioactive particles as well). In such radioactive heavy nuclei, the balance between the strong nuclear force attractive force and the electrostatic repulsive force can be knocked out of equilibrium, by the introduction of energy in the form of an absorbed neutron or photon, the nucleus oscillates in an attempt to regain equilibrium until the electrostatic force gains more power than the shorter-distanced nuclear force, at which point the nucleus splits apart, releasing energy as it does so.
Nuclear fusion is a nuclear reaction in which two light nuclei (such as hydrogen) combine to form a heavier nuclei (such as helium). The process releases excess binding energy from the reaction, based upon the binding energies of the atoms involved in the process.
Oscillation is a motion that repeats itself in a regular cycle, such as a sine wave or pendulum.Also Known As: periodic motion
For a given substance, it is possible to make a phase diagram which outlines the changes in phase (see image to the right). Generally temperature is along the horizontal axis and pressure is along the vertical axis, although three-dimensional phase diagrams can also account for a volume axis. Curves representing the Fusion curve (liquid/solid barrier), the Vaporization curve (liquid/vapor barrier), and the Sublimation curve (solid/vapor barrier) can be seen in the diagram. The area near the origin is the Sublimation curve and it branches off to form the Fusion curve (which goes mostly upward) and the Vaporization curve (when goes mostly to the right). Along the curves, the substance would be in a state of phase equilibrium, balanced precariously between the two states on either side. The point at which all three curves meet is called the triple point. At this precise temperature and pressure, the substance will be in a state of equilibrium between the three states, and minor variations would cause it to shift between them. Finally, the point at which the Vaporization curve ends is called the critical point. The pressure at this point is called the critical pressure and the temperature at this point is the critical temperature. For pressures or temperatures (or both) above these values, essentially there is a blurry line between the liquid and gaseous states. Phase transitions between them do not take place, although the properties themselves can transition between those of liquids and those of gases. They just do not do so in a clear-cut transition, but metamorph gradually from one to another. For more on phase diagrams, including three-dimensional phase diagrams, see our article on states of matter.Also Known As: state diagram
For a given substance, it is possible to make a phase diagram which outlines the changes in phase (see image to the right). Generally temperature is along the horizontal axis and pressure is along the vertical axis, although three-dimensional phase diagrams can also account for a volume axis. Curves representing the Fusion curve (liquid/solid barrier), the Vaporization curve (liquid/vapor barrier), and the Sublimation curve (solid/vapor barrier) can be seen in the diagram. The area near the origin is the Sublimation curve and it branches off to form the Fusion curve (which goes mostly upward) and the Vaporization curve (when goes mostly to the right). Along the curves, the substance would be in a state of phase equilibrium, balanced precariously between the two states on either side. The point at which all three curves meet is called the triple point. At this precise temperature and pressure, the substance will be in a state of equilibrium between the three states, and minor variations would cause it to shift between them. Finally, the point at which the Vaporization curve ends is called the critical point. The pressure at this point is called the critical pressure and the temperature at this point is the critical temperature. For pressures or temperatures (or both) above these values, essentially there is a blurry line between the liquid and gaseous states. Phase transitions between them do not take place, although the properties themselves can transition between those of liquids and those of gases. They just do not do so in a clear-cut transition, but metamorph gradually from one to another. For more on phase diagrams, including three-dimensional phase diagrams, see our article on states of matter.Also Known As: state diagram
Under the photon theory of light, a photon is a discrete bundle (or quantum) of electromagnetic (or light) energy. Photons are always in motion and, in a vacuum, have a constant speed of light to all observers, at the vacuum speed of light (more commonly just called the speed of light) of c = 2.998 x 108 m/s.
Basic Properties of PhotonsAccording to the photon theory of light, photons . . .
History of PhotonsThe term photon was coined by Gilbert Lewis in 1926, though the concept of light in the form of discrete particles had been around for centuries and had been formalized in Newton's construction of the science of optics. In the 1800s, however, the wave properties of light (by which I mean electromagnetic radiation in general) became glaringly obvious and scientists had essentially thrown the particle theory of light out the window. It wasn't until Albert Einstein explained the photoelectric effect and realized that light energy had to be quantized that the particle theory returned.
Wave-Particle Duality in BriefAs mentioned above, light has properties of both a wave and a particle. This was an astounding discovery and is certainly outside the realm of how we normally perceive things. Billiard balls act as particles, while oceans act as waves. Photons act as both a wave and a particle all the time (even though it's common, but basically incorrect, to say that it's sometimes a wave and sometimes a particle depending upon which features are more obvious at a given time). Just one of the effects of this wave-particle duality (or particle-wave duality) is that photons, though treated as particles, can be calculated to have frequency, wavelength, amplitude, and other properties inherent in wave mechanics.
The photon is an elementary particle, despite the fact that it has no mass. It cannot decay on its own, although the energy of the photon can transfer (or be created) upon interaction with other particles. Photons are electrically neutral and are one of the rare particles that are identical to their antiparticle, the antiphoton.
Plasma is a distinct phase of matter, separate from the traditional solids, liquids, and gases. It is a collection of charged particles that respond strongly and collectively to electromagnetic fields, taking the form of gas-like clouds or ion beams. Since the particles in plasma are electrically charged (generally by being stripped of electrons), it is frequently described as an ionized gas. Plasma was first identified (as radiant mattter) by Sir William Crookes in 1879. Sir J.J. Thomson identified the nature of the matter in 1897. It was Irving Langmuir who assigned the term plasma in 1928. It is odd to consider that plasma is actually the most common phase of matter, especially since it was the last one discovered. Flame, lightning, interstellar nebulae, stars, and even the empty vastness of space are all examples of the plasma state of matter.
The positron is the antimatter particle of the electron. It has a positive charge of +1, a spin of 1/2, and an identical mass as the electron. When a positron and electron of equal energy interact, they will annihilate each other.
Potential energy, or stored energy, is the ability of a system to do work due to its position or internal structure. For example, gravitational potential energy is a stored energy determined by an object's position in a gravitational field while elastic potential energy is the energy stored in a spring. As a form of energy, the SI units for potential energy are the joule (J) or newton-meter (N*m).
Power is the time rate at which work is done or energy is transferred. In calculus terms, power is the derivative of work with respect to time. The SI unit of power is the watt (W) or joule per second (J/s). Horsepower is a unit of power in the British system of measurement.
Pressure is force per unit area. The SI unit of pressure is the pascal (Pa), which is equivalent to N/m2.
Quarks are one of two fundamental particles in physics. They join together to form hadrons, such as protons and neutrons. The study of quarks and the interactions between them is called quantum chromodynamics. The anti-particle of a quark is the antiquark. Quarks and antiquarks are the only two fundamental particles that interact through all four fundamental forces of physics. Quarks exhibit confinement, which means that the quarks are not observed independently but always in combination with other quarks. This makes determining the properties (mass, spin, and parity) impossible to measure directly; these traits must be inferred from the particles composed of them. These measurements indicate a non-integer spin (either +1/2 or -1/2), so quarks are fermions and follow the Pauli Exclusion Principle. There are 6 flavours of quarks: up, down, strange, charm, bottom, and top. The flavour of the quark determines its properties. Quarks with a charge of +(2/3)e are called up-type quarks and those with a charge of -(1/3)e are called down-type. There are three generations of quarks, based on pairs of weak positive/negative weak isospin. The first generation are up and down quarks, the second generation are strange and charm quarks, the third generation are top and bottom quarks. All quarks have a baryon number (B = 1/3) and a lepton number (L = 0). The flavour determines certain other unique properties, described in individual descriptions.
A quasar is an astronomical entity that emits incredibly high levels of electromagnetic radiation (including light). The amount of energy emitted by a quasar dwarfs even the brightest stars, making them favorites of astrophysicists and cosmologists who wish to study distant space. There are over 60,000 known quasars, all of which appear to be very distant from us (based upon the observed redshift). The closest known quasar is 780 million light-years away. Many scientists believe that the quasars are created by matter interacting with supermassive black holes. This would appear to explain the high energy output and the rapid variability observed in their luminosity.
A Rydberg state occurs when an atom or molecule becomes excited such that one of the electrons moving into a high principal quantum number orbital. Such a Rydberg atom is extremely sensitive to the influences of external fields, collisions, reactivity, and microwave radiation. As such, atoms in the Rydberg states are of interest in a wide range of modern experiments. This excited state is named after Johannes Rydberg, who devised the Rydberg formula in 1888. This formula depicts the change in energy of an excited atom and, therefore, was useful in determining the energy of a photon released during such excitation. In the Rydberg formula, the value n represents the principal quantum number.Also Known As: Rydberg Atom
The specific gravity of a material is the ratio of its density to the density of water (1.00 x 103 kg/m3). This ratio is a pure number, containing no units.
Spectroscopy is the use of light, sound or particle emission to study matter. The emissions are, in many cases, able to provide information about the properties of the matter under investigation. The device often used for such analysis is a spectrometer, which records the spectrum of light emitted (or absorbed) by a given material, especially in analytical chemistry and physical chemistry fields, where the light can be used to determine the chemical composition of a substance because of signature spectral lines emitted by known elements. Similar devices, called spectrographs, are frequently incorporated into major telescopes, and can similarly be used to identify the composition of stars and other astronomical bodies, based on the light they emit.
Distance travelled per unit time. Speed is the scalar quantity that is the magnitude of the velocity vector. The SI units for speed are m / s (meters per second).
A strange quark (symbol s) is a second generation quark with the following properties:
Sublimation is the term for when matter undergoes a phase transition directly from a solid to gaseous form, or vapor, without passing through the more common liquid phase between the two. It is a specific case of vaporization. The most well known example of a material that undergoes sublimation is dry ice, or frozen carbon dioxide.
A superfluid is a special phase of matter in which, when cooled to temperatures near absolute zero, the molecules exhibit strange quantum effects. Some superfluids, such as helium-4 (helium with 4 nucleons - 2 protons and 2 neutrons), are bosons and therefore form a Bose-Einstein condensate when cooled into liquid form. One effect of this is that the viscosity of superfluid helium-4 becomes zero, meaning that normal rules of surface tension, such as capillarity, are no longer obeyed. A superfluid in a glass tube will literally crawl up the side of the tube in a thin film because of this property. Other superfluids, such as helium-3, are fermions, but they can also exhibit superfluid properties due to other quantum effects that are part of the BCS theory of superconducitivity.
Surface tension is a phenomenon in which the surface of a liquid, where the liquid is in contact with gas, acts like a thin elastic sheet. This term is typically used only when the liquid surface is in contact with gas (such as the air). If the surface is between two liquids (such as water and oil), it is called interface tension.
Causes of Surface TensionVarious intermolecular forces, such as Van der Waals forces, draw the liquid particles together. Along the surface, the particles are pulled toward the rest of the liquid, as shown in the picture to the right. Surface tension (denoted with the Greek variable gamma) is defined as the ratio of the surface force F to the length d along which the force acts : gamma = F / d
Units of Surface Tension Surface tension is measured in SI units of N/m (newton per meter), although the more common unit is the cgs unit dyn/cm (dyne per centimeter). In order to consider the thermodynamics of the situation, it is sometimes useful to consider it in terms of work per unit area. The SI unit in that case is the J/m2 (joules per meter squared). The cgs unit is erg/cm2. These forces bind the surface particles together. Though this binding is weak - it's pretty easy to break the surface of a liquid after all - it does manifest in many ways.
Examples of Surface Tension Drops of water. When using a water dropper, the water does not flow in a continuous stream, but rather in a series of drops. The shape of the drops is caused by the surface tension of the water. The only reason the drop of water isn't completely spherical is because of the force of gravity pulling down on it. In the absence of gravity, the drop would minimize the surface area in order to minimize tension, which would result in a perfectly spherical shape. Insects walking on water. Several insects are able to walk on water, such as the water strider. Their legs are formed to distribute their weight, causing the surface of the liquid to become depressed, minimizing the potential energy to create a balance of forces so that the strider can move across the surface of the water without breaking through the surface. This is similar in concept to wearing snow shoes to walk across deep snowdrifts without your feet sinking.
Temperature is a measurement of the average kinetic energy of the molecules in an object or system and can be measured with a thermometer or a calorimeter. It is a means of determining the internal energy contained within the system.
Heat vs. TemperatureNote that temperature is different from heat, though the two concepts are linked. Temperature is a measure of the internal energy of the system, while heat is a measure of how energy is transferred from one system (or body) to another. The greater the heat absorbed by a material, the more rapidly the atoms within the material begin to move, and thus the greater the rise in temperature.
Temperature ScalesSeveral temperature scales exist. In America, the Fahrenheit temperature is most commonly used, though the SI unit Centrigrade (or Celsius) is used by us in Australia and in most of the rest of the world. The Kelvin scale is used often in physics, and is adjusted so that 0 degrees Kelvin is absolute zero.
A top quark (symbol t) is a third generation quark with the following properties
Torque is the tendency of a force to cause or change rotational motion of a body. Torque is calculated by multiplying Force and distance, so the SI units of torque are newton-meters, or N*m (even though this is the same as joules, torque isn't work or energy, so should just be newton-meters).Also Known As: Moment
An up quark (symbol u) is a first generation quark with the following properties
Van der Waals' forces are a group of relatively weak intermolecular interactions which generally result when a molecule or group of molecules become polarized into a magnetic dipole. This happens most often due to uneven or shifting distributions within the electron cloud of the atoms. These sorts of interactions were first documented by Johannes Diderik van der Waals, a Dutch physicist and chemist, after whom they were named. Originally the name referred to all intermolecular interactions, though it has over the years come to mean the more specific group of interactions resulting from temporary dipole interactions.Also Known As: London disperson forces,Keesom forces,Debye forces
Vaporization is the transition of matter from a solid or liquid phase into a gaseous (or vapor) phase. Water boiling into steam is an example of vaporization. Sublimation is the more specific name for the vaporization directly from the solid phase to the gaseous phase.
A vector is a mathematical quantity that has both a magnitude and direction. It is often represented in variable form in boldface with an arrow above it. Many quantities in physics are vector quantities. A unit vector is a vector with a magnitude of 1 and is often denoted in boldface with a carat (^) above the variable.
Velocity is a vector measurement of the rate and direction of motion or, in other terms, the rate and direction of the change in the position of an object. The scalar (absolute value) magnitude of the velocity vector is the speed of the motion. In calculus terms, velocity is the first derivative of position with respect to time. The SI units for velocity are m / s (meters per second).
Velocity is a vector measurement of the rate and direction of motion or, in other terms, the rate and direction of the change in the position of an object. The scalar (absolute value) magnitude of the velocity vector is the speed of the motion. In calculus terms, velocity is the first derivative of position with respect to time. The SI units for velocity are m / s (meters per second).
Work is defined (in calculus terms) as the integral of the force over a distance of displacement. In the case of a constant force, work is the scalar product of the force acting on an object and the displacement caused by that force. Though both force and displacement are vector quantities, work has no direction due to the nature of a scalar product (or dot product) in vector mathematics. This definition is consistent with the proper definition, because a constant force integrates to merely the product of the force and distance. The SI units for work are the joule (J) or newton-meter (N * m), from the function W = F * s where W is work, F is force, and s is the displacement. The joule is also the SI unit of energy.
A wormhole is a theoretical entity allowed by Einstein's theory of general relativity in which spacetime curvature connects two distant locations (or times).The name wormhole was coined by American theoretical physicist John A. Wheeler in 1957, based on an analogy of how a worm could chew a hole from one end of an apple through the center to the other end, thus creating a shortcut through the intervening space. The picture to the right depicts a simplified model of how this would work in linking two areas of two-dimensional space.
The most common concept of a wormhole is an Einstein-Rosen bridge, first formalized by Albert Einstein and his colleague Nathan Rosen in 1935. In such a model, a black hole would draw matter in while being connected to a white hole in a distant location, which expels this same matter. In 1962, John A. Wheeler and Robert W. Fuller were able to prove that such a wormhole would collapse instantly upon formation, so not even light would make it through.
In a 1988 paper, physicists Kip Thorne and Mike Morris proposed since that such a wormhole could be made stable by containing some form of negative matter or energy (sometimes called exotic matter). Other types of traversible wormholes have also been proposed as valid solutions to the general relativity field equations. Some solutions to the general relativity field equations have suggested that wormholes could also be created to connect different times, as well as distant space. Still other possibilities have been proposed of wormholes connecting to whole other universes. There is still much speculation on whether it is possible for wormholes to actually exist and, if so, what properties they would actually possess.
Also Known As Einstein-Rosen bridge, Schwarzschild wormhole, Lorentzian wormhole, Morris-Thorne wormhole