Units of measurement

Basic Quantities are:

Length (Meter, Foot)
Time (Second)
Mass (Kilogram, Slug)
Force (Newton, Pound force)

Units:

Basic quantities (force, mass, length, time) are related by Newton’s second law.
Units used to measure quantities are not all independent.
Three of four units, called base units, are arbitrarily defined and the fourth is derived.

Units:

SI Units:
Modern version of metric system,
Base units are Meter or m for length, Second or s for time and Kilogram or kg for mass,
Acceleration of gravity:

           g = 9.8   m/ s2

Force is derived quantity measured in unit called Newton:

          1 N = 1  kg . m  / s2

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 U.S. Customary Units (fps):
Base units are length, time and force,
feet (ft), second (s), and pound (lb),
Acceleration of gravity:

           g = 32.2     ft / s2

Mass is derived quantity measured in a unit called a slug:

           1  slug = 1  lb . s2 / ft

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Systems of Units, (Summary):

Name Length Time Mass Force
SI meter (m) second (s) kilogram (kg) Newton (N)
US Customary foot (ft) second (s) slug (lb.s2/ft) pound (lb)

Unit conversions:

Force:          1 lb = 4.4482 N

Mass:          1 slug = 14.5938 kg

length:          1 ft = 0.3048 m

 

 

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