Physical Quantity Conversion

Unit Conversion

• Chain-link conversion is a method used to change the units of a physical quantity.
• In this method, the original measurement is multiplied by a conversion factor, which is a ratio of units equal to unity.
• Conversion factors can be used to cancel unwanted units in a conversion.

Examples of Conversion Factors

• 1 min = 60 s, so the ratios (1 min)/(60 s) and (60 s)/(1 min) can be used as conversion factors.
• These conversion factors can be used to convert between units, such as converting 2 min to seconds: 2 min = (2 min)(1) = (2 min)(60 s / 1 min) = 120 s.

Important Notes

• When introducing a conversion factor, make sure unwanted units cancel; if not, invert the factor and try again.
• Units obey the same algebraic rules as variables and numbers in conversions.

History of the Meter

• In 1792, the Republic of France established a new system of weights and measures with the meter as its cornerstone.
• The meter was initially defined as one ten-millionth of the distance from the north pole to the equator.
• Later, the definition was changed to be the distance between two fine lines on a platinum-iridium bar, the standard meter bar.

Standardization of the Meter

• The standard meter bar was kept at the International Bureau of Weights and Measures near Paris.
• Accurate copies of the bar were sent to standardizing laboratories around the world.
• These secondary standards were used to produce more accessible standards, ultimately allowing for widespread use of the meter.