Discrepancy vs. Disparity

Discrepancy vs. Disparity Discrepancy vs. Disparity Discrepancy vs. Disparity By Mark Nichol What’s the difference between discrepancy and disparity and other similar words beginning with the prefix dis-? The meanings are often the same or closely related, but some distinctions apply: Discrepancy, the noun form of the rarely used adjective discrepant, stems from the Latin term discrepare, which means â€Å"to sound discordantly.† A discrepancy is a variance from or disagreement with something, as in the discrepancy between inventory figures and actual stock, or between a statement on a certain issue and a record of a previous comment about the same topic. Disparity is a noun form of the adjective disparate. (Disparateness is its more unwieldy synonym.) The root of these words is the Latin term parare, which means â€Å"to prepare.† Although disparate means â€Å"different† or â€Å"distinct,† disparity has a more precise connotation, one of inequality. Meanwhile, a dissimilarity or dissimilitude (the root of these terms is the Latin word similis, the basis of same, similar, simulate, and resemblance) is a lack, respectively, of commonality and resemblance. Distinctness and distinctiveness (both, like distinguish, from the Latin word distinguere, meaning â€Å"to separate, to prick apart†) have similar rather than distinct meanings: Distinctness refers to notability, an unmistakable quality or phenomenon, or a separateness; distinctiveness, meanwhile, also refers to a markedly singular trait but may alternatively apply to a stylishness or other state that sets something apart. In an bygone era of unregulated spelling, discreet and discrete were originally alternate spellings for the word meaning â€Å"separate, distinct,† but the former form eventually took on a specialized sense, one of â€Å"careful, prudent.† The latter form is often erroneously used in place of the well-established variant spelling for that meaning. Want to improve your English in five minutes a day? Get a subscription and start receiving our writing tips and exercises daily! Keep learning! Browse the Misused Words category, check our popular posts, or choose a related post below:Congratulations on or for?Does "Mr" Take a Period?One "L" or Two?

Impulse - Force Over Time

Impulse - Force Over Time Force applied over time creates an impulse, a change in momentum. Impulse is defined in classical mechanics as a force multiplied by the amount of time it acts over. In calculus terms, the impulse can be calculated as the integral of force with respect to time.  The symbol for impulse is J or Imp.   Force is a vector quantity (the direction matters) and impulse is also a vector in the same direction. When an impulse is applied to an object, it has a vector change in its linear momentum. Impulse is the product of the average net force acting on an object and its duration.  J  Ã‚  F̅Δt Alternately, impulse can be calculated as the difference in momentum between two given instances.  Impulse change in momentum force x time. Units of Impulse The SI unit of impulse is the same as for momentum, the Newton second N*s or kg*m/s. The two terms are equal. English engineering units for impulse are pound-second (lbf*s) and slug-foot per second (slug*ft/s). The Impulse-Momentum Theorem This theorem is logically equivalent to Newtons second law of motion: force equals mass times acceleration, also known as the force law. The change in momentum of an object equals the impulse applied to it.  J  Ã‚  ÃŽâ€ p. This theorem can be applied to a constant mass or to a changing mass. It is relevant especially to rockets, where the mass of the rocket changes as fuel is expended to produce the thrust. Impulse of Force The product of average force and the time in which it is exerted is the impulse of force. It is equal to the change of momentum of an object that isnt changing mass. This is a useful concept when you are studying impact forces. If you increase the time over which the change of force happens, the impact force also decreases. This is used in mechanical design for safety, and it is useful in sports applications as well. You want to reduce the impact force for a car hitting guardrail, for example, by designing the guardrail to collapse as well as designing parts of the car to crumple on impact. This lengthens the time of the impact and therefore the force. If you want a ball to be propelled further, you want to shorten the time of impact with a racket or bat, raising the impact force. Meanwhile, a boxer knows to lean away from a punch so it takes longer in landing, reducing the impact. Specific Impulse Specific impulse is a measure of the efficiency of rockets and jet engines. It is the total impulse that is produced by a unit of propellant as it is consumed. If a rocket has a higher specific impulse, it needs less propellant to gain altitude, distance, and speed. It is the equivalent of the thrust divided by the propellant flow rate. If the propellant weight is used (in Newton or pound), specific impulse is measured in seconds. This is often how rocket engine performance is reported by manufacturers.