Question #37b98

1 Answer
Oct 3, 2016

The FPS units of measurement are the foot, pound, and second.


The FPS (foot–pound–second) system is built on three fundamental units:

  • foot for length
  • (avoirdupois) pound for mass
  • second for time.


The foot is defined as being equivalent exactly to 0.3048 m.

One foot represents a length of twelve inches, and three feet equal one yard.

Avoirdupois Pound

The international avoirdupois pound is defined as exactly 0.453 592 37 kg.

One pound is divided into sixteen ounces.


The second is defined as the time that elapses during #"9.192 631 770" × 10^9# vibrations of the radiation produced by a transition between two levels of the cesium-133 atom.

There are sixty seconds in a minute, sixty minutes in an hour, and twenty-four hours in a day.

The SI

The corresponding SI units are the metre, kilogram, and second.


The metre is defined as the distance traveled by light in a vacuum
in #1/"299 792 458"# seconds.


The kilogram is defined as being equal to the mass of the International Prototype Kilogram (IPK), a platinum-iridium cylinder that is kept in a high-security vault outside Paris.

1 kg = 1000 g, and 1 g = 1000 mg


The definition of the second is the same in both the FPS system and the SI.

The Big Differences

(a) FPs is not coherent

In a coherent system of units, all derived units are derived by simple multiplication or division without only "1" as a proportionality factor.

For example, in the SI, the standard unit of volume is #"1 m"^3".

In the FPS system, the gallon is not equal to a cubic yard or the cube of any length unit.

(b) SI fractions and multiples of units are expressed as powers of 10.

1 km = 1000 m; 1 m = 1000 mm, etc.

In the FPs system, 1 mi = 1760 yd; 1 yd = 3 ft; 1 ft = 12 in.