Sir I s a a c Newto n’s Book I.

54

thus found, the motion of each body after the stroke is de-termined, as before.

10. In the next place, suppose the bodies A and B wereboth moving the fame way, but A with a swifter motion, soas to overtake B, and strike against it. The effect os the per-cussion or stroke, when die bodies are. not elastic, is discover-ed by finding the common motion, which the two bodieswould have after the stroke, if B were at rest, and A were toadvance against it with a velocity equal to the excess of thepresent velocity of A above die velocity of B ; and by ad-ding to this common velocity thus found the velocity of B.

11, If the bodies are elastic, the effect of the elasticity isto be united with this other, as in the former cafes.

ll. When the bodies are perfectly elastic, the rule ofH u y g e n s * in this cafe is to prolong C D ( fig. 7. ) and totake in it thus prolonged C E in the fame proportion to E D,as the greater velocity of A bears to the leffer velocity of B ;after which FG being taken equal to F E, the velocities of thetwo bodies after the stroke will be determined, as in the twopreceding cafes.

13. Thus I have given the sum of what has been writ-ten concerning the effects of percussion, when two bodiesfreely in motion strike directly against each other; and theresults here set down, as the consequence of our reasoning

* In the place above-cited.

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