momentum, conservation of


momentum, conservation of

      general law of physics according to which the quantity called momentum that characterizes motion never changes in an isolated collection of objects; that is, the total momentum of a system remains constant. Momentum is equal to the mass of an object multiplied by its velocity and is equivalent to the force required to bring the object to a stop in a unit length of time. For any array of several objects, the total momentum is the sum of the individual momenta. There is a peculiarity, however, in that momentum is a vector, involving both the direction and the magnitude of motion, so that the momenta of objects going in opposite directions can cancel to yield an overall sum of zero.

      Before launch, the total momentum of a rocket and its fuel is zero. During launch, the downward momentum of the expanding exhaust gases just equals in magnitude the upward momentum of the rising rocket, so that the total momentum of the system remains constant—in this case, at zero value. In a collision of two particles, the sum of the two momenta before collision is equal to their sum after collision. What momentum one particle loses, the other gains.

      The law of conservation of momentum is abundantly confirmed by experiment and can even be mathematically deduced on the reasonable presumption that space is uniform—that is, that there is nothing in the laws of nature that singles out one position in space as peculiar compared with any other.

      There is a similar conservation law for angular momentum, which describes rotational motion in essentially the same way that ordinary momentum describes linear motion. Although the precise mathematical expression of this law is somewhat more involved, examples of it are numerous. All helicopters (helicopter), for instance, require at least two propellers (rotors) for stabilization. The body of a helicopter would rotate in the opposite direction to conserve angular momentum if there were only a single horizontal propeller on top. In accordance with conservation of angular momentum, ice skaters spin faster as they pull their arms toward their body and more slowly as they extend them.

      Angular-momentum conservation has also been thoroughly established by experiment and can be shown to follow mathematically from the reasonable presumption that space is uniform with respect to orientation—that is, that there is nothing in the laws of nature that singles out one direction in space as being peculiar compared with any other.

* * *


Universalium. 2010.

Look at other dictionaries:

  • momentum conservation — judesio kiekio tvermė statusas T sritis fizika atitikmenys: angl. linear momentum conservation; momentum conservation vok. Erhaltung der Bewegungsgröße, f; Impulserhaltung, f rus. сохранение импульса, n; сохранение количества движения, n pranc.… …   Fizikos terminų žodynas

  • momentum conservation law — judesio kiekio tvermės dėsnis statusas T sritis fizika atitikmenys: angl. momentum conservation law; principle of conservation of linear momentum; principle of conservation of momentum vok. Erhaltungssatz der Bewegungsgröße, m;… …   Fizikos terminų žodynas

  • linear momentum conservation — judesio kiekio tvermė statusas T sritis fizika atitikmenys: angl. linear momentum conservation; momentum conservation vok. Erhaltung der Bewegungsgröße, f; Impulserhaltung, f rus. сохранение импульса, n; сохранение количества движения, n pranc.… …   Fizikos terminų žodynas

  • Momentum — This article is about momentum in physics. For other uses, see Momentum (disambiguation). Classical mechanics Newton s Second Law …   Wikipedia

  • conservation law — Physics, Chem. any law stating that some quantity or property remains constant during and after an interaction or process, as conservation of charge or conservation of linear momentum. [1945 50] * * * or law of conservation In physics, the… …   Universalium

  • momentum — /moh men teuhm/, n., pl. momenta / teuh/, momentums. 1. force or speed of movement; impetus, as of a physical object or course of events: The car gained momentum going downhill. Her career lost momentum after two unsuccessful films. 2. Mech. a… …   Universalium

  • Conservation law — For the legal aspects of environmental conservation, see conservation movement. 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… …   Wikipedia

  • conservation of angular momentum — judesio kiekio momento tvermė statusas T sritis fizika atitikmenys: angl. conservation of angular momentum; conservation of moment of momentum vok. Drehimpulserhaltung, f; Erhaltung des Drehimpulses, f rus. сохранение момента количества движения …   Fizikos terminų žodynas

  • conservation of moment of momentum — judesio kiekio momento tvermė statusas T sritis fizika atitikmenys: angl. conservation of angular momentum; conservation of moment of momentum vok. Drehimpulserhaltung, f; Erhaltung des Drehimpulses, f rus. сохранение момента количества движения …   Fizikos terminų žodynas

  • Momentum transfer — Part of Chemical engineering History Concepts Unit operations Unit processes Chemical engineer Chemical process Process integration Unit operation …   Wikipedia


Share the article and excerpts

Direct link
Do a right-click on the link above
and select “Copy Link”

We are using cookies for the best presentation of our site. Continuing to use this site, you agree with this.