Force Influence that can change motion of an object In modern physics, which includes relativity and quantum mechanics, the laws governing motion are revised to rely on fundamental interactions as the ultimate origin of force. However, the understanding of force provided by classical mechanics is useful for practical purposes.[1] Development of the concept [edit] By the early 20th century, Einstein developed a theory of relativity that correctly predicted the action of forces on objects with increasing momenta near the speed of light and also provided insight into the forces produced by gravitation and inertia. Pre-Newtonian concepts Though Aristotelian physics was criticized as early as the 6th century,[9][10] its shortcomings would not be corrected until the 17th century work of Galileo Galilei, who was influenced by the late medieval idea that objects in forced motion carried an innate force of impetus. Newtonian mechanics A modern statement of Newton's second law is a vector equation: where is so
Angular momentum This gyroscope remains upright while spinning due to its angular momentum. In physics, angular momentum, moment of momentum, or rotational momentum[1][2] is a measure of the amount of rotation an object has, taking into account its mass, shape and speed.[3] It is a vector quantity that represents the product of a body's rotational inertia and rotational velocity about a particular axis. The angular momentum of a system of particles (e.g. a rigid body) is the sum of angular momenta of the individual particles. For a rigid body rotating around an axis of symmetry (e.g. the blades of a ceiling fan), the angular momentum can be expressed as the product of the body's moment of inertia, I, (i.e., a measure of an object's resistance to changes in its rotation velocity) and its angular velocity ω: In this way, angular momentum is sometimes described as the rotational analog of linear momentum. Angular momentum in classical mechanics[edit] Definition[edit] and we can see that where
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. 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] The momentum of a system of particles is the sum of their momenta. The momenta of more than two particles can be added in the same way. or so
Torque Torque, moment or moment of force (see the terminology below), is the tendency of a force to rotate an object about an axis,[1] 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. Mathematically, torque is defined as the cross product of the lever-arm distance vector and the force vector, which tends to produce rotation. Loosely speaking, torque is a measure of the turning force on an object such as a bolt or a flywheel. For example, pushing or pulling the handle of a wrench connected to a nut or bolt produces a torque (turning force) that loosens or tightens the nut or bolt. The symbol for torque is typically τ, the Greek letter tau. The magnitude of torque depends on three quantities: the force applied, the length of the lever arm[2] connecting the axis to the point of force application, and the angle between the force vector and the lever arm. where τ is the torque vector and τ is the magnitude of the torque, F is the force vector,
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. There are several distinct phenomena which can be used to measure mass. Inertial mass measures an object's resistance to changes in velocity m=F/a. The mass of an object determines its acceleration in the presence of an applied force. Units of mass[edit] The kilogram is one of the seven SI base units; one of three which is defined ad hoc, without reference to another base unit. The standard International System of Units (SI) unit of mass is the kilogram (kg). Other units are accepted for use in SI: Outside SI system, other units include:
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[edit] 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[edit] There are also approximate conservation laws. See also[edit] References[edit] Victor J. External links[edit] Conservation Laws — an online textbook
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. Mathematically, instantaneous acceleration—acceleration over an infinitesimal interval of time—is the rate of change of velocity over time: where = time.
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.
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. History[edit] Measurement has been important ever since humans settled from nomadic lifestyles and started using building materials; occupying land and trading with neighbours. One of the oldest units of length measurement used in the ancient world was the 'cubit' which was the length of the arm from the tip of the finger to the elbow. After Albert Einstein's special relativity, length can no longer be thought of being constant in all reference frames. Units[edit] See also[edit]
Motion (physics) If the position of a body is not changing 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. Momentum is a quantity which is used for measuring motion of an object. An object's momentum is directly related to the object's mass and velocity, and the total momentum of all objects in an isolated system (one not affected by external forces) does not change with time, as described by the law of conservation of momentum. More generally, motion is a concept that applies to objects, bodies, and matter particles, to radiation, radiation fields and radiation particles, and to space, its curvature and space-time. Motion involves a change in position, such as in this perspective of rapidly leaving Yongsan Station. Classical mechanics is fundamentally based on Newton's laws of motion.
Harmonic oscillator where k is a positive constant. If F is the only force acting on the system, the system is called a simple harmonic oscillator, and it undergoes simple harmonic motion: sinusoidal oscillations about the equilibrium point, with a constant amplitude and a constant frequency (which does not depend on the amplitude). If a frictional force (damping) proportional to the velocity is also present, the harmonic oscillator is described as a damped oscillator. Depending on the friction coefficient, the system can: Oscillate with a frequency smaller than in the non-damped case, and an amplitude decreasing with time (underdamped oscillator).Decay to the equilibrium position, without oscillations (overdamped oscillator). The boundary solution between an underdamped oscillator and an overdamped oscillator occurs at a particular value of the friction coefficient and is called "critically damped." If an external time dependent force is present, the harmonic oscillator is described as a driven oscillator.
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]
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. The mathematical form of this equation varies depending on the type of wave. There are two main types of waves. The second main type of wave, electromagnetic waves, do not require a medium. Further, the behavior of particles in quantum mechanics are described by waves, and researchers believe that gravitational waves also travel through space, although gravitational waves have never been directly detected. General features[edit] A single, all-encompassing definition for the term wave is not straightforward. and
Work (physics) In physics, a force is said to do work when it acts on a body, and there is a displacement of the point of application in the direction of the force. For example, when you lift a suitcase from the floor, the work done on the suitcase is the force it takes to lift it (its weight) times the height that it is lifted. The term work was introduced in 1826 by the French mathematician Gaspard-Gustave Coriolis[1][2] as "weight lifted through a height", which is based on the use of early steam engines to lift buckets of water out of flooded ore mines. The SI unit of work is the newton-metre or joule (J). The work done by a constant force of magnitude F on a point that moves a displacement (not distance) s in the direction of the force is the product, For example, if a force of 10 newtons (F = 10 N) acts along a point that travels 2 metres (s = 2 m), then it does the work W = (10 N)(2 m) = 20 N m = 20 J. Work is closely related to energy. where the symbol Another example is a book on a table. where