impact

im·pact

I0052500 (ĭm′păkt′)n.1. a. The striking of one body against another; collision. See Synonyms at collision.b. The force transmitted by a collision.2. The effect or impression of one person or thing on another: still gauging the impact of automation on the lives of factory workers.v. (ĭm-păkt′, ĭm′păkt′) im·pact·ed, im·pact·ing, im·pacts v.tr.1. To pack firmly together.2. To strike forcefully: meteorites impacting the lunar surface.3. To have an effect or impact on: "No region ... has been more impacted by emerging ... economic trends" (Joel Kotkin).v.intr. To have an effect or impact. See Usage Note below.

[From Latin impāctus, past participle of impingere, to push against; see impinge.]

im·pac′tion n.Usage Note: Impact in the figurative sense of "a dramatic effect" came under criticism in the 1960s, both as a noun and verb. Complaints that the noun was a pointless hyperbole and a vogue word turned out to be short-lived, and this usage is now is standard: in our 2015 survey, 97 percent of the Usage Panel accepted The program might have a positive impact on our nation's youth. (A similar sentence was accepted by 93 percent of the Panel in 2001.) The verb is a different matter. Many people dislike it because they assume it was converted from the noun in the manner of voguish and bureaucratic words like dialogue and interface, but in fact impact was a verb long before it was a noun—the verb dates from the early 1600s, the noun from the late 1700s. Most of the Panelists still disapprove of the intransitive use of the verb meaning "to have an effect": in our 2015 survey, 78 percent of the Panel (down only slightly from 85 percent in 2001) rejected These policies are impacting on our ability to achieve success. The transitive version was once as vilified, but is gradually becoming more acceptable: in 2015, only 50 percent (down from 80 percent in 2001) rejected The court ruling will impact the education of minority students, and only 39 percent (down from 66 percent in 2001) found the literal sense unacceptable in the sentence Thousands of meteors have impacted the lunar surface. Although resistance to the transitive senses is waning, the intransitive use is still strongly disliked and is best avoided. See Usage Notes at contact, impactful.

impact

n 1. the act of one body, object, etc, striking another; collision 2. the force with which one thing hits another or with which two objects collide 3. the impression made by an idea, cultural movement, social group, etc: the impact of the Renaissance on Medieval Europe. vb 4. to drive or press (an object) firmly into (another object, thing, etc) or (of two objects) to be driven or pressed firmly together 5. to have an impact or strong effect (on) [C18: from Latin impactus pushed against, fastened on, from impingere to thrust at, from pangere to drive in] imˈpaction n

im•pact

(n. ˈɪm pækt; v. ɪmˈpækt)
n. 1. the striking of one thing against another; collision. 2. influence; effect: the impact of Einstein on modern physics. 3. a forcible impinging: the tremendous impact of the shot. 4. the force exerted by a new idea, concept, technology, or ideology: the impact of the industrial revolution. v.t. 5. to drive or press closely or firmly into something. 6. to fill up; congest. 7. to collide with: a rocket designed to impact the planet Mars. 8. to have an impact or effect on; influence: The decision may impact your whole career. v.i. 9. to make contact forcefully. 10. to have an impact: Increased demand will impact on sales. [1775–85; back formation from impacted] usage: The verb impact has developed the transitive sense “to have an impact or effect on” (The new reading program has impacted the elementary schools favorably) and the intransitive sense “to have an impact or effect” (Our work here impacts on every department in the company) These uses, though common, are often harshly criticized.

impact

fighting fire with fire - Early American settlers had to put out great prairie fires and learned that setting a circle or strip of land on fire could stop the path or lessen the impact of a big fire—giving us the phrase "fighting fire with fire."
freezing rain - Rain that freezes on impact with the ground or objects.
draw - The billiard ball's recoil after impact.
impinge, infringe - To impinge is to come into contact or encroach or have an impact; to infringe is to encroach on a right or privilege or to violate.

impact

Past participle: impacted
Gerund: impacting

Imperative
impact
impact

Present
I impact
you impact
he/she/it impacts
we impact
you impact
they impact

Preterite
I impacted
you impacted
he/she/it impacted
we impacted
you impacted
they impacted

Present Continuous
I am impacting
you are impacting
he/she/it is impacting
we are impacting
you are impacting
they are impacting

Present Perfect
I have impacted
you have impacted
he/she/it has impacted
we have impacted
you have impacted
they have impacted

Past Continuous
I was impacting
you were impacting
he/she/it was impacting
we were impacting
you were impacting
they were impacting

Past Perfect
I had impacted
you had impacted
he/she/it had impacted
we had impacted
you had impacted
they had impacted

Future
I will impact
you will impact
he/she/it will impact
we will impact
you will impact
they will impact

Future Perfect
I will have impacted
you will have impacted
he/she/it will have impacted
we will have impacted
you will have impacted
they will have impacted

Future Continuous
I will be impacting
you will be impacting
he/she/it will be impacting
we will be impacting
you will be impacting
they will be impacting

Present Perfect Continuous
I have been impacting
you have been impacting
he/she/it has been impacting
we have been impacting
you have been impacting
they have been impacting

Future Perfect Continuous
I will have been impacting
you will have been impacting
he/she/it will have been impacting
we will have been impacting
you will have been impacting
they will have been impacting

Past Perfect Continuous
I had been impacting
you had been impacting
he/she/it had been impacting
we had been impacting
you had been impacting
they had been impacting

Conditional
I would impact
you would impact
he/she/it would impact
we would impact
you would impact
they would impact

Past Conditional
I would have impacted
you would have impacted
he/she/it would have impacted
we would have impacted
you would have impacted
they would have impacted

Thesaurus

Noun	1.	impact - the striking of one body against anotherblow, bump - an impact (as from a collision); "the bump threw him off the bicycle"slam - a forceful impact that makes a loud noiseimpinging, striking, contact - the physical coming together of two or more things; "contact with the pier scraped paint from the hull"
	2.	impact - a forceful consequence; a strong effect; "the book had an important impact on my thinking"; "the book packs a wallop"wallopconsequence, effect, result, upshot, outcome, event, issue - a phenomenon that follows and is caused by some previous phenomenon; "the magnetic effect was greater when the rod was lengthwise"; "his decision had depressing consequences for business"; "he acted very wise after the event"
	3.	impact - influencing strongly; "they resented the impingement of American values on European culture"impingement, encroachmentinfluence - causing something without any direct or apparent effort
	4.	impact - the violent interaction of individuals or groups entering into combat; "the armies met in the shock of battle"shockfighting, combat, fight, scrap - the act of fighting; any contest or struggle; "a fight broke out at the hockey game"; "there was fighting in the streets"; "the unhappy couple got into a terrible scrap"
Verb	1.	impact - press or wedge together; pack togetherwedge, squeeze, force - squeeze like a wedge into a tight space; "I squeezed myself into the corner"
	2.	impact - have an effect upon; "Will the new rules affect me?"affect, bear upon, bear on, touch on, touchalter, change, modify - cause to change; make different; cause a transformation; "The advent of the automobile may have altered the growth pattern of the city"; "The discussion has changed my thinking about the issue"strike a blow - affect adversely; "The court ruling struck a blow at the old segregation laws"repercuss - cause repercussions; have an unwanted effecttell on - produce an effect or strain on somebody; "Each step told on his tired legs"redound - have an effect for good or ill; "Her efforts will redound to the general good"stimulate, excite - act as a stimulant; "The book stimulated her imagination"; "This play stimulates"process, treat - subject to a process or treatment, with the aim of readying for some purpose, improving, or remedying a condition; "process cheese"; "process hair"; "treat the water so it can be drunk"; "treat the lawn with chemicals" ; "treat an oil spill"hydrolise, hydrolize - make a compound react with water and undergo hydrolysistinge, color, colour, distort - affect as in thought or feeling; "My personal feelings color my judgment in this case"; "The sadness tinged his life"endanger, peril, queer, scupper, expose - put in a dangerous, disadvantageous, or difficult positionhit, strike - affect or afflict suddenly, usually adversely; "We were hit by really bad weather"; "He was stricken with cancer when he was still a teenager"; "The earthquake struck at midnight"subject - cause to experience or suffer or make liable or vulnerable to; "He subjected me to his awful poetry"; "The sergeant subjected the new recruits to many drills"; "People in Chernobyl were subjected to radiation"discommode, disoblige, incommode, inconvenience, put out, trouble, bother - to cause inconvenience or discomfort to; "Sorry to trouble you, but..."act upon, influence, work - have and exert influence or effect; "The artist's work influenced the young painter"; "She worked on her friends to support the political candidate"slam-dunk - make a forceful move against; "the electronic travel market is slam-dunking traditional travel agencies"

impact

noun1. effect, influence, consequences, impression, repercussions, ramifications They expect the meeting to have a marked impact on the country's future.2. collision, force, contact, shock, crash, knock, stroke, smash, bump, thump, jolt The pilot must have died on impact.verb1. hit, strike, crash, clash, crush, ram, smack, collide the sharp tinkle of metal impacting on stoneimpact on something or someone affect, change, involve, interest, concern, influence, transform, alter, modify, act on, sway, bear upon, impinge upon Such schemes mean little unless they impact on people.

impact

noun1. Violent forcible contact between two or more things:bump, collision, concussion, crash, jar, jolt, percussion, shock, smash.2. The strong effect exerted by one person or thing on another:force, impression, influence, repercussion.3. The capacity to create a powerful effect:Informal: punch, wallop.

Translations

影响影响力效果碰撞

impact

(ˈimpӕkt) noun1. (the force of) one object etc hitting against another. The bomb exploded on impact.碰撞2. a strong effect or impression. The film had quite an impact on television viewers. 效果，影响

impact

→ 影响力zhCN

Impact

A force, also known as impulsive force, which acts only during a short time interval but which is sufficiently large to cause an appreciable change in the momentum of the system on which it acts. The momentum change produced by the impulsive force is described by the momentum-impulse relation. See Collision (physics), Impulse (mechanics)

Impact

a forceful collision between two bodies. In English the term “impact” is also sometimes applied to the impulsive forces acting in collisions. The concept of impact need not be restricted to the collision of solid bodies. For example, we may speak of the impact of a jet of fluid on a solid body and the impact of a solid body on the surface of a liquid. The Russian term for impact—udar—also has the meaning of shock and consequently is applied to a number of additional phenomena, such as a water hammer and the action of an explosion or shock wave on a body.

The interval of time during which an impact occurs is small and usually ranges from several ten thousandths to a few millionths of a second. The impulsive forces acting at the areas of contact of colliding bodies, however, are very large. These forces vary within broad limits during the time of impact and reach values such that the average pressure (stresses) at the areas of contact is of the order of 10⁴ or even 10⁵ kilograms-force/cm² (1 kilogram-force/cm² = 10⁵ newtons/m²).

During the time of contact, the action of the impulsive forces causes a substantial change in the velocities of the points of a body. Other possible consequences of impact include permanent deformation, the production of sound waves, the heating of the bodies, and the occurrence of changes in the mechanical properties of the materials composing the bodies. When the impact speed exceeds its critical value, a body will fracture at the place of impact. The critical speeds for metals range from about 15 m/sec, in the case of copper, to about 150 m/sec or more, in the case of high-grade steels.

The change in the velocities of points of a body during impact can be determined by methods of the general theory of impact. As a measure of the mechanical interaction of bodies during impact, these methods use not the impulsive force P but the impact impulse S, which is the impulse of the force during the time of impact T. Since T is small, the impulses of all external forces (such as gravity) and the displacements of the points of the body during the impact are disregarded. The basic equations of the general theory of impact follow from theorems on the change of the momentum and angular momentum of a system in a collision. The velocities after the impact can be found by means of these theorems when the applied impact impulse and the velocities before impact are known. If the body is not free, the impulsive constraints can also be found.

When two bodies collide, the collision can be divided into two periods. The first period begins at the instant that points A and B of the bodies (see Figure 1) come into contact. At this instant their rate of approach is v_An – v_Bn, where v_An and v_Bn are the

Figure 1. Impact between two bodies

components of the velocities v_A and v_B along n, the common normal to the surfaces of the bodies at A and B. This normal is known as the line of impact. By the end of the first period, the bodies have ceased moving toward each other, and part of their kinetic energy has been transformed into potential energy of deformation. In the second period, the reverse transformation occurs: the potential energy of elastic deformation is transformed into kinetic energy of the bodies, which are now separating. At the end of the second period, points A and B are moving apart at the rate V_An – V_Bn. If the bodies are perfectly elastic, the mechanical energy is completely restored by the end of the second period, and ǀV_An – V_Bn = ǀv_An – v_Bnǀ. On the other hand, the impact of perfectly inelastic bodies ends with the first period; in this case, V_An – V_Bn = 0.

When real bodies collide, the mechanical energy is only partially restored by the time the impact ends. The rest of the energy is lost as a result of the permanent deformation of the bodies, the heating of the bodies, and so on. Thus, ǀV_An – V_Bnǀ < ǀv_An – v_Bnǀ. The losses are calculated by introducing the coefficient of restitution k, which is assumed to depend only on the physical properties of the materials of the bodies:

In the case of impact involving a stationary body, V_Bn = v_Bn = 0 and k = – V_An/v_An. The value of k is determined experimentally. One method is to measure the height h reached by a ball in its rebound after falling freely onto a horizontal plate from a height H; in this case, . Experimental data yield the following values of k: 0.5 for wooden balls, 0.55 for steel balls, 0.89 for ivory balls, and 0.94 for glass balls. In the limiting cases of perfectly elastic and perfectly inelastic impacts, k = 1 and 0, respectively. When the velocities before impact and the coefficient k are known, it is possible to determine the velocities after impact and the impact impulse S acting at the points of collision.

If the centers of gravity C₁ and C₂ of two colliding bodies lie on the line of impact, the impact is said to be central; otherwise it is said to be eccentric. If the velocities v_x and v₂ of the centers of gravity before impact are directed parallel to the line of impact, the impact is said to be direct; otherwise it is said to be oblique. In the direct central impact of two smooth spherical bodies 1 and 2,

where ΔT is the kinetic energy lost by the system during the impact and M₁ and M₂ are the masses of the spheres. In the special case where k = 1 and M₁ = M₂, we have V₁ = v₂ and V₂ = v₁. In other words, spheres with identical masses exchange velocities during a perfectly elastic collision, and ΔT = 0.

To determine the duration of impact, the impulsive forces, and the stresses and deformations that the forces produce in the bodies, it is necessary to take into account the mechanical properties of the materials of the bodies, the changes in the properties during the impact, and the nature of the initial and boundary conditions. The solution of the problem is complicated not only by purely mathematical difficulties but also by the lack of sufficient data on the parameters governing the behavior of the materials of the bodies under impact loading. Consequently, a number of simplifying assumptions must be introduced into the calculations.

The most highly developed theory of impact is that dealing with perfectly elastic bodies. This theory assumes that the bodies obey the laws of elastic deformation during impact and that permanent deformation does not occur. A deformation at the region of contact propagates through such a body as an elastic wave at a speed that depends on the physical properties of the material. If the time required for the wave to pass through the entire body is much less than the duration of the impact, the influence of elastic vibrations may be neglected, and the nature of the contact interactions during impact may be considered to be the same as in static loading. H. Hertz’ contact theory of impact is based on these assumptions. If the time required for elastic waves to pass through the body is comparable to the duration of the impact, the wave theory of impact is used for calculations.

The collision of bodies that are not perfectly elastic is a considerably more complicated problem and requires taking both elastic and plastic properties of materials into account. In solving this problem and the associated problems of determining the mechanical properties of the materials of the bodies during impact, studies of the structural changes in the bodies and of fracture processes rely extensively on the analysis and generalization of the results of numerous experimental investigations. Experimental studies are also carried out on the specific characteristics of impulsive loading at high speeds (of the order of hundreds of meters per second) and in explosions. In the case of direct contact between the explosive charge and the body, the explosion can be considered equivalent to a collision at speeds of up to 1,000 m/-sec.

In addition to the collision of bodies, collisions of molecules, atoms, and elementary particles are studied in physics (see also ATOMIC COLLISION).

REFERENCES

Kil’chevskii, N. A. Teoriia soudarenii tverdykh tel. Leningrad-Moscow, 1949.
Dinnik, A. N. Udar i szhatie uprugikh tel. lzbr. trudy, vol. 1. Kiev, 1952.
Davidenkov, N. N. Dinamicheskie ispytaniia metallov, 2nd ed. Leningrad-Moscow, 1936.
Il’iushin, A. A., and V. S. Lenskii. Soprotivlenie materialov. Moscow, 1959. Chapter 6.
Rinehart, J., and J. Pearson. Povedenie metallov pri impul’sivnykh nagruzkakh. Moscow, 1958. (Translated from English.)

S. M. TARG

impact

[′im‚pakt] (mechanics) A forceful collision between two bodies which is sufficient to cause an appreciable change in the momentum of the system on which it acts. Also known as impulsive force.

impact

im·pact

impact

im•pact

impact

impact

impact

impact

impact

impact

impact

upon impact

have an impact on (someone or something)

impact (up)on (someone or something)

have an impact on someone or something

impact (up)on someone or something

upon impact

impact on

Impact

Impact

Impact

REFERENCES

impact

impact

im·pact

IMPACT

IMPACT

im·pact

Patient discussion about impact

ImPACT

impact

Synonyms for impact

noun effect

Synonyms

noun collision

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verb hit

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phrase impact on something or someone

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Synonyms for impact

noun violent forcible contact between two or more things

Synonyms

noun the strong effect exerted by one person or thing on another

Synonyms

noun the capacity to create a powerful effect

Synonyms

Synonyms for impact

noun the striking of one body against another

Related Words

noun a forceful consequence

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noun influencing strongly

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noun the violent interaction of individuals or groups entering into combat

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verb press or wedge together

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verb have an effect upon

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