Hello,

in which cases can I omit an article (a\an\the) at the beginning of the sentence starting with a noun in singular?

Examples (from Wikipedia about velocity) :

"Average velocity magnitude is always smaller than or equal to average speed of a given particle."

"Instantaneous velocity is always tangential to trajectory."

"Relative velocity is a measurement of velocity between two objects as determined in a single coordinate system."

" The transverse velocity is the component of velocity along a circle centered at the origin."

"The magnitude of the transverse velocity is that of the cross product of the unit vector in the direction of the displacement and the velocity vector."

I am confused!