. Chambers's encyclopedia; a dictionary of universal knowledge for the people. !, which tends to diaw thebody downwards towards the earth. The force ofprojection acts only at the commencement of thebodys motion ; the force of gravity, on the contrary,continues to act effectively during the whole timeof the bodys motion, drawing it further and furtherfrom its original direction, and causing it to describea curved path, which, if the body moved in avacuum, would be accurately a parabola. This isreadily seen by considering fig. 1, in which Are[)resents the point from which the body is pro-jected
. Chambers's encyclopedia; a dictionary of universal knowledge for the people. !, which tends to diaw thebody downwards towards the earth. The force ofprojection acts only at the commencement of thebodys motion ; the force of gravity, on the contrary,continues to act effectively during the whole timeof the bodys motion, drawing it further and furtherfrom its original direction, and causing it to describea curved path, which, if the body moved in avacuum, would be accurately a parabola. This isreadily seen by considering fig. 1, in which Are[)resents the point from which the body is pro-jected (suppose the embrasure of a fort); AB thedirection of projection (horizontal in this in-stance) ; Al the distance which would be passedover by the projectile in unit of time if gravitydid not act; 1—2, the distance which would. similarly be described in second unit of time ; 2—3,3—4, &c. the distances corresponding to the third,fourth, &c. ixnits of time—all these distances beingnecessarily equal, from the impulsive nature of theforce of projection; Al, again, represents the dis-tance which the projectile would fall under theaction of gravity alone in the first unit of time;1—2 the distance due to gravity in the second unitof time; 2—3 the distance due to the third unit, &c.,tlie distances A1, A2, A3, &c., being in the propor-tion of 1, 4, 9, &c. (see Falling Bodies) ; hence, bythe well-known principle of the Composition of Forcesand Velocities (q. v.), we find at once, by comjtletingthe series of parallelograms, that at the end of thelirst unit of time the body is at c, at the end of thesecond at h, at the end of the third at e, &c. Kow,as the lines Vc, 2b, 3e, &c. increase as the numbers1, 2, 3, &c., and the lines Al, A2, A3, &c. as thenumbers 1^, 2-, 3-,
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