why does the cable car have to use the directcurrent? But is not the alternating

This is because the motor rotational speed is not easy to control, butthe direct current motor rotational speed can along with thesize but automatically changes. For example, when on cable car bridge,uphill or starting, the load can be very big, by now the electricmotor rotational speed could automatically reduce speed, couldautomatically strengthen through the electric motor electric current,causes the electric motor the power suitably to enlarge drives thecable car. When the cable car gets down from the bridge, the downhillperhaps goes when the flat land, transfers lightly, by nowthe electric motor rotational speed could automatically speed up,causes the cable car to go quick. Because the direct current electrically operated function along withdrives person's will to speed up or to reduce speed, causes the cablecar safely to go, therefore the cable car power source must use thedirect current.