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Re: when to write radians



Since numerical representations of all physical quantities,
in the SI system, are ratios then no units would be necessary
if only basic SI were used. For example, v=25 would imply,
automatically, 25 m/s, and not 25 km/s. Likewise for other
physical quantities, such acceleration or current. But I am
not suggesting this silly convention. Units are useful.

1) Decibels are often used to express ratios of two
physical quantities (expressed in the same units).
For example, currents, pressures and voltages.

2) When we say "a length of a corridor is 20 meters"
we are referring to a ratio of two lengths, that of
the corridor and that of a stick, our secondary
standard of length. Why don't we add "radians,"
"decibels" or "machs?" Because this would not
be useful.

Ludwik Kowalski