History of physics
Natural philosophy has its origins in Greece during the Archaic period, (650 BCE – 480 BCE), when Pre-Socratic philosophers like Thales rejected non-naturalistic explanations for natural phenomena and proclaimed that every event had a natural cause.They proposed ideas verified by reason and observation and many of their hypotheses proved successful in experiment, for example atomism.
Classical physics became a separate science when early modern Europeans used these experimental and quantitative methods to discover what are now considered to be the laws of physics. Kepler, Galileo and more specifically Newton discovered and unified the different laws of motion. During the industrial revolution, as energy needs increased, so did research, which led to the discovery of new laws in thermodynamics, chemistry and electromagnetic.
Modern physics started with the works of Max Planck in quantum theory and Einstein in relativity, and continued in quantum mechanics pioneered by Heisenberg, Schrodinger and Paul Dirac.
Philosophy of physics
In many ways, physics stems from ancient Greek philosophy. From Thales' first attempt to characterize matter, to Democritus' deduction that matter ought to reduce to an invariant state, the Ptolemaic astronomy of a crystalline firmament, and Aristotle's book Physics (an early book on physics, which attempted to analyze and define motion from a philosophical point of view), various Greek philosophers advanced their own theories of nature. Physics was known as natural philosophy until the late 18th century.
By the 19th century physics was realized as a discipline distinct from philosophy and the other sciences. Physics, as with the rest of science, relies on philosophy of science to give an adequate description of the scientific method.The scientific method employs a prior reasoning as well as a posterior reasoning and the use of Bayesian inference to measure the validity of a given theory.
The development of physics has answered many questions of early philosophers, but has also raised new questions. Study of the philosophical issues surrounding physics, the philosophy of physics, involves issues such as the nature of space and time, determinism, and metaphysical outlooks such as empiricism, naturalism and realism.
Many physicists have written about the philosophical implications of their work, for instance Laplace, who championed causal determinism, and Erwin Schrodinger, who wrote on quantum mechanics. The mathematical physicist Roger Penrose has been called a Platonist by Stephen Hawking, a view Penrose discusses in his book, The Road to Reality. Hawking refers to himself as an "unashamed reductionist" and takes issue with Penrose's views.
Glossary of physics terms
Absolute zero- The theoretical lowest possible temperature. More formally, it is the theoretical temperature at which entropy reaches its minimum value.
Acceleration- The rate at which the velocity of a body changes with time.
Alpha particle- Consist of two protons and two neutrons bound together into a particle identical to a helium nucleus, which is classically produced in the process of alpha decay, but may be produced also in other ways and given the same name.
Alternating current- A form of electric current in which the movement of electric charge periodically reverses direction.
Ammeter- An instrument that is used to measure current.
Ampere- A unit that describes the rate of flow of electricity (current).
Atom- A basic unit of matter that consists of a dense central nucleus surrounded by a cloud of negatively charged electrons. The atomic nucleus contains a mix of positively charged protons and electrically neutral neutrons.
Atom- A basic unit of matter that consists of a dense central nucleus surrounded by a cloud of negatively charged electrons. The atomic nucleus contains a mix of positively charged protons and electrically neutral neutrons.
Babinet's principle- A theorem concerning diffraction that states that the diffraction pattern from an opaque body is identical to that from a hole of the same size and shape except for the overall forward beam intensity.
Background radiation- The ubiquitous ionising radiation that the general population is exposed to.
Barometer- A scientific instrument used in meteorology to measure atmospheric pressure. Pressure tendency can forecast short term changes in the weather.
Beam- A structural element that is capable of withstanding load primarily by resisting bending.Beams are traditionally descriptions of building or civil engineering structural elements, but smaller structures such as truck or automobile frames, machine frames, and other mechanical or structural systems contain beam structures that are designed and analyzed in a similar fashion.
Bending- (also known as flexure) The behavior of a slender structural element subjected to an external load applied perpendicularly to a longitudinal axis of the element.
Beta particle- High-energy, high-speed electrons or positrons emitted by certain types of radioactive nuclei.
Big Bang- The prevailing cosmological model that describes the early development of the Universe.
Binary star- A binary star is a star system consisting of two stars orbiting around their common centre of mass.
Binding energy- The mechanical energy required to disassemble a whole into separate parts. A bound system typically has a lower potential energy than the sum of its constituent parts.
Black hole- A region of space-time where gravity prevents anything, including light, from escaping.
Black-body radiation- The type of electromagnetic radiation within or surrounding a body in thermodynamic equilibrium with its environment, or emitted by a black body (an opaque and non-reflective body) held at constant, uniform temperature. The radiation has a specific spectrum and intensity that depends only on the temperature of the body.
Block and tackle- A system of two or more pulleys with a rope or cable threaded between them, usually used to lift or pull heavy loads.
Boson- One of two classes of elementary particles, the other being fermions. An important characteristic of bosons is that there is no limit to the number that can occupy the same quantum state.
British thermal unit- A traditional unit of energy equal to about 1055 joules. It is the amount of energy needed to heat one pound of water by one degree Fahrenheit. In scientific contexts the Btu has largely been replaced by the SI unit of energy, the joule.
Brittle- A material is brittle if, when subjected to stress, it breaks without significant Brittle materials absorb relatively little energy prior to fracture, even those of high strength. Breaking is often accompanied by a snapping sound.
Brownian motion- The presumably random moving of particles suspended in a fluid (liquid or gas) resulting from their bombardment by the fast-moving atoms or molecules in the gas or liquid. Also called pedesis.
Bulk modulus- A measure of a substance's resistance to uniform compression. It is defined as the ratio of the infinitesimal pressure increase to the resulting relative decrease of the volume. Its base unit is the pascal.
Buoyancy- An upward force exerted by a fluid, that opposes the weight of an immersed object.
Cathode- An electrode through which electric current flows out of a polarized electrical device. The direction of electric current is, by convention, opposite to the direction of electron flow. Therefore the electrons flow into the polarized electrical device and out of, for example, the connected electrical circuit.
Celsius scale- A scale and unit of measurement for temperature, also known as Centigrade.
Center of gravity- The point in a body around which the resultant torque due to gravity forces vanish. Near the surface of the earth, where the gravity acts downward as a parallel force field, the center of gravity and the center of mass are the same.
Center of mass- A distribution of mass in space is the unique point where the weighted relative position of the distributed mass sums to zero.
Centigrade- A scale and unit of measurement for temperature, also known as Celsius.
Centrifugal force- ("center fleeing") The apparent outward force that draws a rotating body away from the centre of rotation. It is caused by the inertia of the body as the body's path is continually redirected.
Centripetal force- ("center seeking") A force which keeps a body moving with a uniform speed along a circular path and is directed along the radius towards the centre.
Chain reaction- A sequence of reactions where a reactive product or by-product causes additional reactions to take place.
Coulomb- The SI derived unit of electric charge. It is defined as the charge transported by a steady current of one ampere in one second.
Crest- The point on a wave with the maximum value or upward displacement within a cycle.
Critical mass- The smallest amount of fissile material needed for a sustained nuclear chain reaction.
DC motor- A mechanically commutated electric motor powered from direct current (DC)
Deflection- The degree to which a structural element is displaced under a load. It may refer to an angle or a distance.
Density- The mass density or density of a material is its mass per unit volume. Mathematically, density is defined as mass divided by volume.
Displacement (fluid)- Occurs when an object is immersed in a fluid, pushing it out of the way and taking its place. The volume of the fluid displaced can then be measured, and from this the volume of the immersed object can be deduced (the volume of the immersed object will be exactly equal to the volume of the displaced fluid).
Displacement (vector)- The shortest distance from the initial to the final position of a point. Thus, it is the length of an imaginary straight path, typically distinct from the path actually traveled by.
Distance- A numerical description of how far apart objects are.
Doppler effect- The change in frequency of a wave (or other periodic event) for an observer moving relative to its source.The received frequency is higher (compared to the emitted frequency) during the approach, it is identical at the instant of passing by, and it is lower during the recession.
Drag- Forces which act on a solid object in the direction of the relative fluid flow velocity. Unlike other resistive forces, such as dry friction, which is nearly independent of velocity, drag forces depend on velocity.
Ductility- A solid material's ability to deform under tensile stress; this is often characterized by the material's ability to be stretched into a wire.
Elasticity- A physical property of materials which return to their original shape after they are deformed.
Electric charge- A physical property of matter that causes it to experience a force when near other electrically charged matter. There exist two types of electric charges, called positive and negative.
Electric circuit- An electrical network consisting of a closed loop, giving a return path for the current.
Electric current- A flow of electric charge through a conductive medium.
Electric field- The region of space surrounding electrically charged particles and time-varying magnetic fields. The electric field depicts the force exerted on other electrically charged objects by the electrically charged particle the field is surrounding.
Electrical conductor- A conductor is a material which contains movable electric charges, and therefore can conduct an electric current, under the influence of an electric field.
Electrical insulator- A material whose internal electric charges do not flow freely, and which therefore does not conduct an electric current, under the influence of an electric field.
Electric power- The rate at which electric energy is transferred by an electric circuit.
Electrical network- An interconnection of electrical elements such as resistors, inductors, capacitors, voltage sources, current sources and switches.
Electrical resistance- The opposition to the passage of an electric current through an electrical element.
Electricity- The set of physical phenomena associated with the presence and flow of electric charge.
Electromagnet- A type of magnet in which the magnetic field is produced by the flow of electric current.
Electromagnetic field- (also EMF or EM field) A physical field produced by moving electrically charged objects.
Electromagnetic radiation- (EM radiation or EMR) Electromagnetic radiation is a form of energy emitted and absorbed by charged particles, which exhibits wave-like behavior as it travels through space.
Electron- A subatomic particle with a negative elementary electric charge.
Electron volt- (symbol eV) A unit of energy equal to approximately 1.6×10−19 joule (symbol J). By definition, it is the amount of energy gained by the charge of a single electron moved across an electric potential difference of one volt.
Electronegativity- A chemical property that describes the tendency of an atom or a functional group to attract electrons (or electron density) towards itself.
Electronics- A field that deals with electrical circuits that involve active electrical components such as vacuum tubes, transistors, diodes and integrated circuits, and associated passive interconnection technologies.
Endothermic - A process or reaction in which the system absorbs energy from its surroundings in the form of heat.
Escape velocity- The speed at which the kinetic energy plus the gravitational potential energy of an object is zero. It is the speed needed to "break free" from a gravitational field without further propulsion.
Exothermic- ("outside heating") A process or reaction that releases energy from the system, usually in the form of heat, but also in the form of light, electricity, or sound.
Natural philosophy has its origins in Greece during the Archaic period, (650 BCE – 480 BCE), when Pre-Socratic philosophers like Thales rejected non-naturalistic explanations for natural phenomena and proclaimed that every event had a natural cause.They proposed ideas verified by reason and observation and many of their hypotheses proved successful in experiment, for example atomism.
Classical physics became a separate science when early modern Europeans used these experimental and quantitative methods to discover what are now considered to be the laws of physics. Kepler, Galileo and more specifically Newton discovered and unified the different laws of motion. During the industrial revolution, as energy needs increased, so did research, which led to the discovery of new laws in thermodynamics, chemistry and electromagnetic.
Modern physics started with the works of Max Planck in quantum theory and Einstein in relativity, and continued in quantum mechanics pioneered by Heisenberg, Schrodinger and Paul Dirac.
Philosophy of physics
In many ways, physics stems from ancient Greek philosophy. From Thales' first attempt to characterize matter, to Democritus' deduction that matter ought to reduce to an invariant state, the Ptolemaic astronomy of a crystalline firmament, and Aristotle's book Physics (an early book on physics, which attempted to analyze and define motion from a philosophical point of view), various Greek philosophers advanced their own theories of nature. Physics was known as natural philosophy until the late 18th century.
By the 19th century physics was realized as a discipline distinct from philosophy and the other sciences. Physics, as with the rest of science, relies on philosophy of science to give an adequate description of the scientific method.The scientific method employs a prior reasoning as well as a posterior reasoning and the use of Bayesian inference to measure the validity of a given theory.
The development of physics has answered many questions of early philosophers, but has also raised new questions. Study of the philosophical issues surrounding physics, the philosophy of physics, involves issues such as the nature of space and time, determinism, and metaphysical outlooks such as empiricism, naturalism and realism.
Many physicists have written about the philosophical implications of their work, for instance Laplace, who championed causal determinism, and Erwin Schrodinger, who wrote on quantum mechanics. The mathematical physicist Roger Penrose has been called a Platonist by Stephen Hawking, a view Penrose discusses in his book, The Road to Reality. Hawking refers to himself as an "unashamed reductionist" and takes issue with Penrose's views.
Glossary of physics terms
Absolute zero- The theoretical lowest possible temperature. More formally, it is the theoretical temperature at which entropy reaches its minimum value.
Acceleration- The rate at which the velocity of a body changes with time.
Alpha particle- Consist of two protons and two neutrons bound together into a particle identical to a helium nucleus, which is classically produced in the process of alpha decay, but may be produced also in other ways and given the same name.
Alternating current- A form of electric current in which the movement of electric charge periodically reverses direction.
Ammeter- An instrument that is used to measure current.
Ampere- A unit that describes the rate of flow of electricity (current).
Atom- A basic unit of matter that consists of a dense central nucleus surrounded by a cloud of negatively charged electrons. The atomic nucleus contains a mix of positively charged protons and electrically neutral neutrons.
Atom- A basic unit of matter that consists of a dense central nucleus surrounded by a cloud of negatively charged electrons. The atomic nucleus contains a mix of positively charged protons and electrically neutral neutrons.
Babinet's principle- A theorem concerning diffraction that states that the diffraction pattern from an opaque body is identical to that from a hole of the same size and shape except for the overall forward beam intensity.
Background radiation- The ubiquitous ionising radiation that the general population is exposed to.
Barometer- A scientific instrument used in meteorology to measure atmospheric pressure. Pressure tendency can forecast short term changes in the weather.
Beam- A structural element that is capable of withstanding load primarily by resisting bending.Beams are traditionally descriptions of building or civil engineering structural elements, but smaller structures such as truck or automobile frames, machine frames, and other mechanical or structural systems contain beam structures that are designed and analyzed in a similar fashion.
Bending- (also known as flexure) The behavior of a slender structural element subjected to an external load applied perpendicularly to a longitudinal axis of the element.
Beta particle- High-energy, high-speed electrons or positrons emitted by certain types of radioactive nuclei.
Big Bang- The prevailing cosmological model that describes the early development of the Universe.
Binary star- A binary star is a star system consisting of two stars orbiting around their common centre of mass.
Binding energy- The mechanical energy required to disassemble a whole into separate parts. A bound system typically has a lower potential energy than the sum of its constituent parts.
Black hole- A region of space-time where gravity prevents anything, including light, from escaping.
Black-body radiation- The type of electromagnetic radiation within or surrounding a body in thermodynamic equilibrium with its environment, or emitted by a black body (an opaque and non-reflective body) held at constant, uniform temperature. The radiation has a specific spectrum and intensity that depends only on the temperature of the body.
Block and tackle- A system of two or more pulleys with a rope or cable threaded between them, usually used to lift or pull heavy loads.
Boson- One of two classes of elementary particles, the other being fermions. An important characteristic of bosons is that there is no limit to the number that can occupy the same quantum state.
British thermal unit- A traditional unit of energy equal to about 1055 joules. It is the amount of energy needed to heat one pound of water by one degree Fahrenheit. In scientific contexts the Btu has largely been replaced by the SI unit of energy, the joule.
Brittle- A material is brittle if, when subjected to stress, it breaks without significant Brittle materials absorb relatively little energy prior to fracture, even those of high strength. Breaking is often accompanied by a snapping sound.
Brownian motion- The presumably random moving of particles suspended in a fluid (liquid or gas) resulting from their bombardment by the fast-moving atoms or molecules in the gas or liquid. Also called pedesis.
Bulk modulus- A measure of a substance's resistance to uniform compression. It is defined as the ratio of the infinitesimal pressure increase to the resulting relative decrease of the volume. Its base unit is the pascal.
Buoyancy- An upward force exerted by a fluid, that opposes the weight of an immersed object.
Cathode- An electrode through which electric current flows out of a polarized electrical device. The direction of electric current is, by convention, opposite to the direction of electron flow. Therefore the electrons flow into the polarized electrical device and out of, for example, the connected electrical circuit.
Celsius scale- A scale and unit of measurement for temperature, also known as Centigrade.
Center of gravity- The point in a body around which the resultant torque due to gravity forces vanish. Near the surface of the earth, where the gravity acts downward as a parallel force field, the center of gravity and the center of mass are the same.
Center of mass- A distribution of mass in space is the unique point where the weighted relative position of the distributed mass sums to zero.
Centigrade- A scale and unit of measurement for temperature, also known as Celsius.
Centrifugal force- ("center fleeing") The apparent outward force that draws a rotating body away from the centre of rotation. It is caused by the inertia of the body as the body's path is continually redirected.
Centripetal force- ("center seeking") A force which keeps a body moving with a uniform speed along a circular path and is directed along the radius towards the centre.
Chain reaction- A sequence of reactions where a reactive product or by-product causes additional reactions to take place.
Coulomb- The SI derived unit of electric charge. It is defined as the charge transported by a steady current of one ampere in one second.
Crest- The point on a wave with the maximum value or upward displacement within a cycle.
Critical mass- The smallest amount of fissile material needed for a sustained nuclear chain reaction.
DC motor- A mechanically commutated electric motor powered from direct current (DC)
Deflection- The degree to which a structural element is displaced under a load. It may refer to an angle or a distance.
Density- The mass density or density of a material is its mass per unit volume. Mathematically, density is defined as mass divided by volume.
Displacement (fluid)- Occurs when an object is immersed in a fluid, pushing it out of the way and taking its place. The volume of the fluid displaced can then be measured, and from this the volume of the immersed object can be deduced (the volume of the immersed object will be exactly equal to the volume of the displaced fluid).
Displacement (vector)- The shortest distance from the initial to the final position of a point. Thus, it is the length of an imaginary straight path, typically distinct from the path actually traveled by.
Distance- A numerical description of how far apart objects are.
Doppler effect- The change in frequency of a wave (or other periodic event) for an observer moving relative to its source.The received frequency is higher (compared to the emitted frequency) during the approach, it is identical at the instant of passing by, and it is lower during the recession.
Drag- Forces which act on a solid object in the direction of the relative fluid flow velocity. Unlike other resistive forces, such as dry friction, which is nearly independent of velocity, drag forces depend on velocity.
Ductility- A solid material's ability to deform under tensile stress; this is often characterized by the material's ability to be stretched into a wire.
Elasticity- A physical property of materials which return to their original shape after they are deformed.
Electric charge- A physical property of matter that causes it to experience a force when near other electrically charged matter. There exist two types of electric charges, called positive and negative.
Electric circuit- An electrical network consisting of a closed loop, giving a return path for the current.
Electric current- A flow of electric charge through a conductive medium.
Electric field- The region of space surrounding electrically charged particles and time-varying magnetic fields. The electric field depicts the force exerted on other electrically charged objects by the electrically charged particle the field is surrounding.
Electrical conductor- A conductor is a material which contains movable electric charges, and therefore can conduct an electric current, under the influence of an electric field.
Electrical insulator- A material whose internal electric charges do not flow freely, and which therefore does not conduct an electric current, under the influence of an electric field.
Electric power- The rate at which electric energy is transferred by an electric circuit.
Electrical network- An interconnection of electrical elements such as resistors, inductors, capacitors, voltage sources, current sources and switches.
Electrical resistance- The opposition to the passage of an electric current through an electrical element.
Electricity- The set of physical phenomena associated with the presence and flow of electric charge.
Electromagnet- A type of magnet in which the magnetic field is produced by the flow of electric current.
Electromagnetic field- (also EMF or EM field) A physical field produced by moving electrically charged objects.
Electromagnetic radiation- (EM radiation or EMR) Electromagnetic radiation is a form of energy emitted and absorbed by charged particles, which exhibits wave-like behavior as it travels through space.
Electron- A subatomic particle with a negative elementary electric charge.
Electron volt- (symbol eV) A unit of energy equal to approximately 1.6×10−19 joule (symbol J). By definition, it is the amount of energy gained by the charge of a single electron moved across an electric potential difference of one volt.
Electronegativity- A chemical property that describes the tendency of an atom or a functional group to attract electrons (or electron density) towards itself.
Electronics- A field that deals with electrical circuits that involve active electrical components such as vacuum tubes, transistors, diodes and integrated circuits, and associated passive interconnection technologies.
Endothermic - A process or reaction in which the system absorbs energy from its surroundings in the form of heat.
Escape velocity- The speed at which the kinetic energy plus the gravitational potential energy of an object is zero. It is the speed needed to "break free" from a gravitational field without further propulsion.
Exothermic- ("outside heating") A process or reaction that releases energy from the system, usually in the form of heat, but also in the form of light, electricity, or sound.
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