For instance, the motion of a spacecraft, regarding its orbit and attitude , is described by the relativistic theory of classical mechanics, while the analogous movements of an atomic nucleus are described by quantum mechanics.
According to the NHS, the average Briton walks between 3,000 and 4,000 steps a day - significantly less than the Fitbit target. Yet many people do significantly more, and for them 10,000 steps might not be much of a target.
If you are reasonably healthy, 10,000 steps a day is a good goal for you. It is the equivalent of walking about five miles per day. (I say about because the actual distance depends on your stride.) You certainly don't have to take all those steps at once, but accumulate them over the course of the day.