Work is equal to force times the distance through which the force acts.功等于力乘上力作用所通过的距离。
Until then, physicists had postulated boundary conditions in which no force acted on the ends of the strings, leaving them free to flap around.当时，物理学家早已假定了没有力作用在弦两端的边界条件，让弦的末端可以自由摆动。
