Text Box: 1791 The International System (formerly called the Metric System) is the decimal system of weights and measures based on the meter and the kilogram. 1799 A platinum bar with a rectangular cross section and polished parallel ends was made to embody the meter. 1866 By act of the U.S. Congress, the use of the metric system was legalized in this country, but was not made obligatory. 1875 The Treaty of the Meter was signed by seventeen countries, including the United States. 1889 Prototype Meter. Each member country in the International Metric Convention received two copies of the standard. 1960 International Standard of Length as 1,650,763.73 vacuum wavelengths of 86-Kr light. 1980 Helium-Neon laser wavelength was accepted as a length standard. 1983 The path traveled by light in vacuum during a time interval of 1/299,792,458 of a second. Length

The definition of the meter (m), which is the international unit of length, was once defined by a physical artifact - two marks inscribed on a bar of platinum-iridium that is seen below.

 

http://www.nist.gov/pml/wmd/metric/length.cfm

 

Today, the meter (m) is defined in terms of a constant found in nature: the length of the path of light traveled in vacuum during a time interval of 1/299,792,458 of a second. 

 

The length of an object will vary with temperature and pressure.

 

Practical tools that are used to measure length are rulers (line gauges), meter sticks, lasers, surveying rods, calipers, range finders, and others

Questions:

 

1.      A common piece of laboratory apparatus is a 6-inch glass stirring rod. As the United States goes metric, catalog specifi­cations of English-dimensioned materials are converted to metric units. A laboratory aide found that 1 inch = 2.54 cm. Upon calculation, the aide decided to call the 6-inch stirring rod a 15.24-cm stirring rod. All was fine until the stirring rods were ordered from the manufacturer. The cost of 15.24-cm rods was 100 percent higher than 6-inch stirring rods. Why?

 

2.     You have a 24-cm length of plastic tubing. How many of these lengths of plastic tubing would be necessary to repre­sent a total length of 3.60 m?