Temperature. A map of global long term monthly average surface air temperatures in Mollweide projection. A temperature is a numerical measure of hot and cold. Its measurement is by detection of heat radiation or particle velocity or kinetic energy, or by the bulk behavior of a thermometric material. It may be calibrated in any of various temperature scales, Celsius, Fahrenheit, Kelvin, etc. The fundamental physical definition of temperature is provided by thermodynamics. Measurements with a small thermometer, or by detection of heat radiation, can show that the temperature of a body of material can vary from time to time and from place to place within it. Within a body that exchanges no energy or matter with its surroundings, temperature tends to become spatially uniform as time passes. The kinetic theory offers a valuable but limited account of the behavior of the materials of macroscopic systems. Thermal vibration of a segment of proteinalpha helix.
Use in science[edit] Temperature scales[edit] Entropy. Where T is the absolute temperature of the system, dividing an incremental reversible transfer of heat into that system (dQ). (If heat is transferred out the sign would be reversed giving a decrease in entropy of the system.) The above definition is sometimes called the macroscopic definition of entropy because it can be used without regard to any microscopic description of the contents of a system. The concept of entropy has been found to be generally useful and has several other formulations. Entropy was discovered when it was noticed to be a quantity that behaves as a function of state, as a consequence of the second law of thermodynamics. The absolute entropy (S rather than ΔS) was defined later, using either statistical mechanics or the third law of thermodynamics.
In the modern microscopic interpretation of entropy in statistical mechanics, entropy is the amount of additional information needed to specify the exact physical state of a system, given its thermodynamic specification. Acceleration. For example, an object such as a car that starts from standstill, then travels in a straight line at increasing speed, is accelerating in the direction of travel.
If the car changes direction at constant speedometer reading, there is strictly speaking an acceleration although it is often not so described; passengers in the car will experience a force pushing them back into their seats in linear acceleration, and a sideways force on changing direction. If the speed of the car decreases, it is sometimes called deceleration; mathematically it is simply acceleration in the opposite direction to that of motion.[4] Definition and properties[edit] Acceleration is the rate of change of velocity.
At any point on a trajectory, the magnitude of the acceleration is given by the rate of change of velocity in both magnitude and direction at that point. The true acceleration at time t is found in the limit as time intervalΔt → 0 of Δv/Δt divided by the duration of the period Special cases[edit] where. Velocity. If there is a change in speed, direction, or both, then the object has a changing velocity and is said to be undergoing an acceleration. Constant velocity vs acceleration[edit] To have a constant velocity, an object must have a constant speed in a constant direction. Constant direction constrains the object to motion in a straight path (the object's path does not curve). Thus, a constant velocity means motion in a straight line at a constant speed.
For example, a car moving at a constant 20 kilometres per hour in a circular path has a constant speed, but does not have a constant velocity because its direction changes. Distinction between speed and velocity[edit] Speed describes only how fast an object is moving, whereas velocity gives both how fast and in what direction the object is moving.[1] If a car is said to travel at 60 km/h, its speed has been specified. Equation of motion[edit] The average velocity during a time interval is described by the formula: at time and is: , then: can be used. Momentum. Like velocity, linear momentum is a vector quantity, possessing a direction as well as a magnitude by its own weight Linear momentum is also a conserved quantity, meaning that if a closed system is not affected by external forces, its total linear momentum cannot change.
In classical mechanics, conservation of linear momentum is implied by Newton's laws; but it also holds in special relativity (with a modified formula) and, with appropriate definitions, a (generalized) linear momentum conservation law holds in electrodynamics, quantum mechanics, quantum field theory, and general relativity. Newtonian mechanics[edit] Momentum has a direction as well as magnitude. Quantities that have both a magnitude and a direction are known as vector quantities. Single particle[edit] The momentum of a particle is traditionally represented by the letter p. The units of momentum are the product of the units of mass and velocity. Many particles[edit] This is known as Euler's first law.[2][3] Conservation[edit] Force. The original form of Newton's second law states that the net force acting upon an object is equal to the rate at which its momentum changes with time. If the mass of the object is constant, this law implies that the acceleration of an object is directly proportional to the net force acting on the object, is in the direction of the net force, and is inversely proportional to the mass of the object.
As a formula, this is expressed as: where the arrows imply a vector quantity possessing both magnitude and direction. Development of the concept With modern insights into quantum mechanics and technology that can accelerate particles close to the speed of light, particle physics has devised a Standard Model to describe forces between particles smaller than atoms. Pre-Newtonian concepts Aristotle famously described a force as anything that causes an object to undergo "unnatural motion" Aristotelian physics began facing criticism in Medieval science, first by John Philoponus in the 6th century. where. Potential. Potential generally refers to a currently unrealized ability.
The term is used in a wide variety of fields, from physics to the social sciences to indicate things that are in a state where they are able to change in ways ranging from the simple release of energy by objects to the realization of abilities in people. Examples include: In linguistics, the potential moodThe mathematical study of potentials is known as potential theory; it is the study of harmonic functions on manifolds. This mathematical formulation arises from the fact that, in physics, the scalar potential is irrotational, and thus has a vanishing Laplacian — the very definition of a harmonic function.In physics, a potential may refer to the scalar potential or to the vector potential.
In either case, it is a field defined in space, from which many important physical properties may be derived. See also[edit] References[edit] Jump up ^ Kennedy-Moore, E. & Lowenthal, M. (2011). Matter. Before the 20th century, the term matter included ordinary matter composed of atoms and excluded other energy phenomena such as light or sound. This concept of matter may be generalized from atoms to include any objects having mass even when at rest, but this is ill-defined because an object's mass can arise from its (possibly massless) constituents' motion and interaction energies. Thus, matter does not have a universal definition, nor is it a fundamental concept in physics today. Matter is also used loosely as a general term for the substance that makes up all observable physical objects.[1][2] All the objects from everyday life that we can bump into, touch or squeeze are composed of atoms.
This atomic matter is in turn made up of interacting subatomic particles—usually a nucleus of protons and neutrons, and a cloud of orbiting electrons.[3][4] Typically, science considers these composite particles matter because they have both rest mass and volume. Definition Common definition Quarks. Energy. All of the many forms of energy are convertible to other kinds of energy, and obey the conservation of energy. Common energy forms include the kinetic energy of a moving object, the radiant energy carried by light, the potential energy stored by an object's position in a force field,(gravitational, electric or magnetic) elastic energy stored by stretching solid objects, chemical energy released when a fuel burns, and the thermal energy due to an object's temperature. According to mass–energy equivalence, any object that has mass when stationary,(called rest mass) also has an equivalent amount of energy whose form is called rest energy.
Conversely, any additional energy above the rest energy will increase an object's mass. For example, if you had a sensitive enough scale, you could measure an increase in mass after heating an object. Living organisms require available energy to stay alive, such as the energy humans get from food. Forms Some examples of different kinds of energy: History. Electric charge. Electric charge is 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 . Positively charged substances are repelled from other positively charged substances, but attracted to negatively charged substances; negatively charged substances are repelled from negative and attracted to positive.
An object will be negatively charged if it has an excess of electrons , and will otherwise be positively charged or uncharged. The SI unit of electric charge is the coulomb (C), although in electrical engineering it is also common to use the ampere-hour (Ah), and in chemistry it is common to use the elementary charge ( e ) as a unit. The symbol Q is often used to denote a charge. The study of how charged substances interact is classical electrodynamics , which is accurate insofar as quantum effects can be ignored. [ edit ] Overview [ edit ] History [ edit ] Properties and. Mass. In physics, mass (from Greek μᾶζα "barley cake, lump [of dough]") is a property of a physical body which determines the body's resistance to being accelerated by a force and the strength of its mutual gravitational attraction with other bodies.
The SI unit of mass is the kilogram (kg). As mass is difficult to measure directly, usually balances or scales are used to measure the weight of an object, and the weight is used to calculate the object's mass. For everyday objects and energies well-described by Newtonian physics, mass describes the amount of matter in an object. However, at very high speeds or for subatomic particles, special relativity shows that energy is an additional source of mass.
Thus, any stationary body having mass has an equivalent amount of energy, and all forms of energy resist acceleration by a force and have gravitational attraction. There are several distinct phenomena which can be used to measure mass. Units of mass[edit] Other units are accepted for use in SI: Time. The flow of sand in an hourglass can be used to keep track of elapsed time. It also concretely represents the present as being between the past and the future. Time is a dimension in which events can be ordered from the past through the present into the future,[1][2][3][4][5][6] and also the measure of durations of events and the intervals between them.[3][7][8] Time has long been a major subject of study in religion, philosophy, and science, but defining it in a manner applicable to all fields without circularity has consistently eluded scholars.[3][7][8][9][10][11] Nevertheless, diverse fields such as business, industry, sports, the sciences, and the performing arts all incorporate some notion of time into their respective measuring systems.[12][13][14] Some simple, relatively uncontroversial definitions of time include "time is what clocks measure"[7][15] and "time is what keeps everything from happening at once".[16][17][18][19] Temporal measurement and history[edit] World time[edit]
Length. In geometric measurements, length is the longest dimension of an object.[1] In the International System of Quantities, length is any quantity with dimension distance. In other contexts "length" is the measured dimension of an object. For example it is possible to cut a length of a wire which is shorter than wire thickness. Length may be distinguished from height, which is vertical extent, and width or breadth, which are the distance from side to side, measuring across the object at right angles to the length. Length is a measure of one dimension, whereas area is a measure of two dimensions (length squared) and volume is a measure of three dimensions (length cubed). History[edit] Measurement has been important ever since humans settled from nomadic lifestyles and started using building materials; occupying land and trading with neighbours.
After Albert Einstein's special relativity, length can no longer be thought of being constant in all reference frames. Units[edit] See also[edit] Space.