Coupling

Definition and stakes

A signalman,  A voice from the signal-box — A voice from the signal-box… (1874)

“ There is another great danger connected with dispatching goods trains from stations with too many vehicles. To get them in motion the drivers are often compelled to start with a sudden jerk, and many times I have seen the coupling chains snapped in two under such circumstances. With shorter trains the engine would be able to start with ease, and this would greatly lessen the danger of breaking or fracturing the coupling chains. The same observations apply to passenger trains. ”
Source: Wikisource

Thomas D. Cope,  Physics

“ The Couple.—If two equal parallel forces act upon a body along different lines in opposite directions, as in Fig. 68, they have no single resultant or there is no one force that will have the same effect as the two components acting together. A combination of forces of this kind is called a couple. Its tendency is to produce change of rotation in a body. An example is the action upon a compass needle which is rotated by a force which urges one end toward the north and by an equal force which urges the other end toward the south. ”
Source: Gutenberg

Get perspective with Kwize: daily news enlightened by great literature