So dark matter, it doesn't interact with light or electromagnetic forces which is why we can't see or feel it.

暗物质不与光或电磁力相互作用，这就是为什么我们看不到或感觉不到它。

As you rotate the wheel, the plastic moves up and  down the ridges thereby creating a stepped or chattering motion, and the spring applies a  very light force so that the plastic follower stays in contact with the ridges.

当你旋转轮子时， 塑料沿着脊线上下移动， 从而产生阶梯式或颤动的运动，弹簧施加非常轻的力， 使塑料从动件与脊线保持接触。