We do our scientific work at millihertz frequencies (one cycle every 1000 seconds or so). The age of the universe is ~13.6 billion years, which corresponds to ~10^-18 Hz. Thinking about the zero-frequency limit is a useful crutch, but all things are always changing. Materials creep, the Earth deforms, temperature changes, aging happens. There is no DC.
2) Small forces for long times yield great change
We study torques as small as 10^-18 N-m acting on ~100 g objects. A willingness to apply a very weak force for a long time can often yield measurable, often large results.