Physical quantities often have units, and some units are formed by multiplying or dividing other units. For example, the unit for momentum is kg m s-1 and the unit for impulse is N s.
The question is, how do we pluralize them (during conversation)? For example, which of the following is correct?
1: Its momentum is:
a. 15 kilogram meter per second
b. 15 kilograms meter per second
c. 15 kilogram meters per second
d. 15 kilogram meter per seconds2: It receives an impulse of:
a. 10 newton second
b. 10 newtons second
c. 10 newton seconds3: The gravitational constant is:
a. 6.67 × 10-11 newton meter squared per kilogram squared
b. 6.67 × 10-11 newtons meter squared per kilogram squared
c. 6.67 × 10-11 newton meters squared per kilogram squared
d. 6.67 × 10-11 newton meter squared per kilograms squared4: The permeability of free space is:
a. 4π × 10-7 volt second per ampere per meter
b. 4π × 10-7 volts second per ampere per meter
c. 4π × 10-7 volt seconds per ampere per meter
d. 4π × 10-7 volt second per amperes per meter
e. 4π × 10-7 volt second per ampere per meters