Практическая грамматика

Phonetics is the science of sounds.
Optics is a branch of physics; it treats of light.
These nouns are treated as plurals when practical application is meant:
His phonetics are excellent.
The acoustics of this hall are good.
Politics, tactics, gymnastics, athletics are generally regarded as plurals.
“The only politics I understand,” answered Magnus sternly,” are honest politics.” (Norris)

VI. Some nouns have only the singular form:

1. 
   Names of materials: water, milk, wine, snow, bread, air etc.
   
2. 
   Collective nouns: foliage, leafage, shrubbery, brushwood, linen, machinery, furniture, money, youth.
   

Note: The noun “people” in the meaning of люди is always plural.
In the evening some people came to supper; a writer and
two painters with their wives. (Galsworthy)
The noun “people” in the meaning of народ has both numbers (a people - народ, peoples - народы)
Defending of peace is the cause of all peoples of the world.
The French are a Roman people.

3. 
   Abstract nouns: friendship, joy, patriotism, love, kindness, weather, courage, information, progress, news, advice, knowledge etc.
   

When she goes to make little purchases, there is no news for her. (Thackeray)

The information he gave them was to be read in the lamentations. Sabatini.)

VII. A number of nouns in English may through a change or variation of meaning acquire the forms of both numbers, singular and plural (and thus become countable). This is found in the following cases:

1. 
   The noun “hair” is used in the singular (волосы);
   
2. 
   The noun “hairs” is used only with the meaning of a few separate hairs (волосок, волоски).
   

… the girl’s hair was chestnut, almost auburn. (La Mure.)
She has a few gray hairs. She has more hair than wit, and more faults than hairs. (Shakespeare.)

3. 
   Nouns fruit and fish are used in the singular. Plural forms fruits and fishes denote different kinds of fruit and fish
   

We have much fruit this year.
But: The fruits were local, consisting of apples, pears, nuts, and other products of summer… (Hardy)

4. 
   The noun penny (пенс) has two plural forms: