What limits the shortest duration that can be measured manually?

By MUNGAI KIHANYA

The Sunday Nation

Nairobi,

07 February 2021

Last week we saw that it is not possible to send a digital signal (pulsing on and off) at a faster rate than the frequency of the waves carrying it. One thing I should have pointed out is that the term “airwaves” that is used in refence to radio waves is totally wrong!

It suggests that radio waves cause vibrations in the air and that they need the presence of air to travel from one point to another. Well, this is not the case at all. The wave that causes oscillation in the air is normal sound.

Radio waves are vibrations of electromagnetic fields. They do not vibrate the air. They do not need presence of air to travel – otherwise, we would never be able to communicate with satellites in outer space where there is no air. In short, radio waves are not airwaves!

In a somewhat related topic to that of last week, it is also not possible to measure time manually at a higher accuracy than the reaction time of a human being. Now the average human reacts to a visual stimulus in about a fifth of a second (0.2s). Thus, one cannot measure time using a manual stopwatch to a higher accuracy than that.

This is the reason why, up to 1976, timings for athletics races were recorded to the tenth of a second. With manually triggered stopwatches, the best accuracy a highly trained professional umpire could get was a tenth of a second (0.1s). There would be no point calibrating the stopwatch to a smaller value than this.

Then in 1977, the world athletics federation (IAAF) adopted fully automated timing using electronic triggers and the times are now recorded up to one-hundredth of a second (0.01s).

Thus, I was shocked when a form 4 pupil told me that they are required to record their timings to two decimal places of seconds. If professional athletics umpires cannot get that level of accuracy, why should we expect it of high schooler?

On the other side of the argument; it is very possible to measure something to a higher accuracy than that of the measuring device. For example, using an ordinary ruler, I measured the thickness of a rim of photocopying paper and found it to be 5.5cm.

Diving this by the number of papers (500), it turns out that the thickness of one sheet is 0.11mm. The smallest division on my ruler is one millimetre, but I was able to measure to a much small length.