And now the force, in its most general term / is q1q2 over 4 pi epsilon zero, which is the conversion factor r squared.

库仑力的最基本形式,就是，其中r是一个变量。

麻省理工公开课 - 固态化学导论课程节选

Now it's shifting its attention to the lower end: the company just refreshed its mainstream Inspiron R line with optional touchscreens and a slimmed-down form factor.

ENGADGET

One statistical factor is the number of new people the typical sick person infects, known as "R".

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