Take the subway. Get on the train in the front. While the train is moving forward, walk to the rear. During this action, when the distance that the train moves equals the length of the train, the displacement equals zero. According to classic physics, work done by a constant force W=FS cosα, the work performed here equals zero. Regardless of the efforts, in physics, the work doesn’t generate any transformation of energy. In mechanical engineering, “useless work” refers to extra work that has to be done. In common Chinese context, “useless work” implies vain efforts.
Often there are empty billboards on the train. When no poster is placed, the default placeholder is the baseboard of the frame. On the old trains in New York (e.g. D & R), the board is wood grain. In Toronto, board on the 2 line train is metal; board on the 1 line train is plastic which is patterned with the branding of the supplier. The pattern on this plastic board is seamless and it’s randomly but regularly tiled, which looks similar to the messy and blocky composition of web ads, meanwhile opposed to the clear appeal of outdoor advertisements. Make collage out of this pattern and web screenshots to design a new ad poster. Replace the empty billboards with the non-exitent ad.
There are two kinds of signal sounds when using metro pass card to enter the subway — swipe or tap the card. Both of the signal sounds are made up of two notes. One is close to F and F sharp, the interval is almost a minor second. The other one is close to D flat and G, the interval is almost an augmented fourth. These two intervals are easily neglected in the chaos, requiring reminder and concentration to be heard. The movement of these two intervals depends on the passing metro pass holders. Useless minor second and augmented fourth.