Power (physics) Work (physics) Wave. In physics, a wave is a disturbance or oscillation that travels through space and matter, accompanied by a transfer of energy.
Wave motion transfers energy from one point to another, often with no permanent displacement of the particles of the medium—that is, with little or no associated mass transport. They consist, instead, of oscillations or vibrations around almost fixed locations. Waves are described by a wave equation which sets out how the disturbance proceeds over time. Harmonic oscillator. Conservation law. In physics, a conservation law states that a particular measurable property of an isolated physical system does not change as the system evolves.
One particularly important physical result concerning laws of conservation is Noether's theorem, which states that there is a one-to-one correspondence between laws of conservation and differentiable symmetries of physical systems. For example, the conservation of energy follows from the time-invariance of physical systems, and the fact that physical systems behave the same regardless of how they are oriented in space gives rise to the conservation of angular momentum. Exact laws A partial listing of physical laws of conservation that are said to be exact laws, or more precisely have never been [proven to be] violated: Conservation of mass-energy Approximate laws There are also approximate conservation laws.
See also References Torque. Torque, moment or moment of force (see the terminology below), is the tendency of a force to rotate an object about an axis, fulcrum, or pivot.
Just as a force is a push or a pull, a torque can be thought of as a twist to an object. Angular momentum. This gyroscope remains upright while spinning due to its angular momentum.
Energy. There are many forms of energy, but all these types must meet certain conditions such as being convertible to other kinds of energy, obeying conservation of energy, and causing a proportional change in mass in objects that possess it.
Common energy forms include the kinetic energy of a moving object, the radiant energy carried by light and other electromagnetic radiation, the potential energy stored by virtue of the position of an object in a force field such as a gravitational, electric or magnetic field, and the thermal energy comprising the microscopic kinetic and potential energies of the disordered motions of the particles making up matter. Some specific forms of potential energy include elastic energy due to the stretching or deformation of solid objects and chemical energy such as is released when a fuel burns. According to mass–energy equivalence, all forms of energy (not just rest energy) exhibit mass. Forms. 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. 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 Momentum has a direction as well as magnitude. Quantities that have both a magnitude and a direction are known as vector quantities. Single particle 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.
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. Definition and properties 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 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). Length. In geometric measurements, length is the longest dimension of an object. 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. Motion (physics) If the position of a body is not changing with the time with respect to a given frame of reference the body is said to be at rest, motionless, immobile, stationary, or to have constant (time-invariant) position.
An object's motion cannot change unless it is acted upon by a force, as described by Newton's first law. 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, and also the measure of durations of events and the intervals between them. 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. 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. Some simple, relatively uncontroversial definitions of time include "time is what clocks measure" and "time is what keeps everything from happening at once". Temporal measurement and history
Space. A right-handed three-dimensional Cartesian coordinate system used to indicate positions in space. (See diagram description for needed correction.) In the 19th and 20th centuries mathematicians began to examine non-Euclidean geometries, in which space can be said to be curved, rather than flat. According to Albert Einstein's theory of general relativity, space around gravitational fields deviates from Euclidean space. Experimental tests of general relativity have confirmed that non-Euclidean space provides a better model for the shape of space. Newton's law of universal gravitation.
Newton's law of universal gravitation states that any two bodies in the universe attract each other with a force that is directly proportional to the product of their masses and inversely proportional to the square of the distance between them. (Separately it was shown that large spherically symmetrical masses attract and are attracted as if all their mass were concentrated at their centers.) This is a general physical law derived from empirical observations by what Isaac Newton called induction. It is a part of classical mechanics and was formulated in Newton's work Philosophiæ Naturalis Principia Mathematica ("the Principia"), first published on 5 July 1687. (When Newton's book was presented in 1686 to the Royal Society, Robert Hooke made a claim that Newton had obtained the inverse square law from him – see History section below.)
Dimension. The first four spatial dimensions. In mathematics Density. Where ρ is the density, m is the mass, and V is the volume. In some cases (for instance, in the United States oil and gas industry), density is loosely defined as its weight per unit volume, although this is scientifically inaccurate – this quantity is more specifically called specific weight.