Cause it's a rule!!Ugh
Phenomenon is the singular form of phenomena.
Quantum is singular, not singular possessive. The singular possessive form is quantum's.
The noun quantum is the singular form; the plural is quanta.
Pulleys is the plural form; the singular is pulley.
Vortex already is a singular form. The plural can be vortexes or vortices. Both are equally correct.
units
They are a universal form of measurement
In SI units- the meter (m).
The word unit's is the possessive form for the singular noun unit. For example:This unit has its own washer and dryer. The unit's electric bill is the responsibility of the tenant.The plural form is units; the plural possessive form is units'. For example:These units do not have washers and dryers. These units' electric bills are included in the rent.
The singular form of a word is the form which applies only to one object, place, concept, animal, or person. For nouns, the singular form is usually the form which does not end in S. On verbs, the singular form usually ends in an S. Of course, for many words, another word is used instead, like using they as the plural form of he or she. The word they does not end in S.
scale factor
scale drawing
mouse/mice
'Pincer' is singular and 'pincers' usually is used for a set of two pincers; a pair.
A complete rotation of a ray around a point is 360 degrees or pi radians. That defines the two common units of measuring angles. The measurement of an angle is the number of such units between the two rays which form the angle.
It is 50 milliseconds. A decimal representation does not imply a change in the measurement units. If this is required then you need to specify the units into which the quantity is to be converted.
Yes, the noun kilometer is a countable noun (a word that has a singular and a plural form). The plural form for the singular noun kilometer is kilometers.