|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|
|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]|
in physics, the sudden, forceful coming together in direct contact of two bodies, such as, for example, two billiard balls, a golf club and a ball, a hammer and a nail head, two railroad cars when being coupled together, or a falling object and a floor. Apart from the properties of the materials of the two objects, two factors affect the result of impact: the force and the time during which the objects are in contact. It is a matter of common experience that a hard steel ball dropped on a steel plate will rebound to almost the position from which it was dropped, whereas with a ball of putty or lead there is no rebound. The impact between the steel ball and plate is said to be elastic, and that between the putty or lead balls and plate is inelastic, or plastic; between these extremes there are varying degrees of elasticity and corresponding responses to impact. In a perfectly elastic impact (attained only at the atomic level), none of the kinetic energy of the coacting bodies is lost; in a perfectly plastic impact, the loss of kinetic energy is at a maximum.
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