moment

moment in physics and engineering, term designating the product of a quantity and a distance (or some power of the distance) to some point associated with that quantity. The most theoretically useful moments are moments of masses, areas, lines, and forces, including magnetic force. The concept of torque (propensity to turn about a point) is the moment of force. If a force tends to rotate a body about some point, then the moment, or turning effect, is the product of the force and the distance from the point to the direction of the force. The application of this concept is illustrated by pushing open a door: the farther from the hinge the push is applied, the less force is required. The principle of the moment of a force is perhaps best seen in the use of a lever . Extensions of this concept are important in mechanics, in topics such as inertia, center of gravity, equilibrium, and stability of structures, and in architectural problems. The moment of inertia of a body about a point is the sum, for each particle in the body, of the mass of the particle and the square of its distance from the point. The angular momentum of a body about a fixed axis is equal to the product of the momentum and the length of the moment arm (distance from the body to the axis). A torque acting on a rigid body acts to change its angular momentum by producing an angular acceleration.

moment the moment of truth a crisis, a turning-point; a testing situation; from Spanish el momento de la verdad the time of the final sword-thrust in a bullfight.

See also in the heat of the moment.

mo·ment / ˈmōmənt/ • n. 1. a very brief period of time: she was silent for a moment before replying a few moments later he returned to the office. ∎  an exact point in time: she would always remember the moment they met. ∎  an appropriate time for doing something; an opportunity: I was waiting for the right moment. ∎  a particular stage in something's development or in a course of events: one of the great moments in aviation history. 2. formal importance: the issues were of little moment to the electorate. 3. Physics a turning effect produced by a force acting at a distance on an object. ∎  the magnitude of such an effect, expressed as the product of the force and the distance from its line of action to a given point. 4. Statistics a quantity that expresses the average or expected value of the first, second, third, or fourth power of the deviation of each component of a frequency distribution from some given value, typically mean or zero. The first moment is the mean, the second moment the variance, the third moment the skew, and the fourth moment the kurtosis. PHRASES: any moment (or at any moment) very soon. at the (or this) moment at the present time; now. for the moment for now. have one's (or its) moments have short periods that are better or more impressive than others: thanks to his gently comic performance, the film has its moments. in a moment 1. very soon: I'll be back in a moment. 2. instantly: the fugitive was captured in a moment. live for the moment live or act without worrying about the future. the moment —— as soon as ——: the heavens opened the moment we left the house. moment of truth a time when a person or thing is tested, a decision has to be made, or a crisis has to be faced. not a moment too soon almost too late. not for a (or one) moment not at all; never. of the moment currently popular, famous, or important: the buzzword of the moment. one moment (or just a moment) a request for someone to wait for a short period of time, esp. to allow the speaker to do or say something.