Measurements and Units of Measure

Some preliminary comments on the course (the syllabus is posted elsewhere):
        The text is Halliday, Resnick & Walker, “Fundamentals of Physics”,
7th edition. Some students have the 6th edition, and I will try to accommodate that. Generally the material should much the same, but I have just recently seen the 7th edition - I have used the 6th, so I don't really know. I suspect that if you know someone with a current edition that you can compare with, you will be OK. It's usually the homework problem numbers that get changed.
        
        Labs begin next week. You need a computation notebook for the labs - they should be available in the bookstore. Stringent requirements are put on lab notebooks in industry - we will relax them somewhat here.
        
        There are seven standard units of measurement in the SI system of units - the one we will use. They are:
        
        The meter - to measure length
        The second - to measure time
        The kilogram - to measure mass
        The mol - to measure the quantity of matter
        The Kelvin - to measure temperature
        The candela - to measure luminous intensity
        The Ampere - to measure electrical quantities

For openers we will use the most fundamental three:
        
        The meter - to measure length. The meter is defined as the distance light travels in 1/2.99792458×108 seconds. This definition requires that the speed of light be accurately known. This speed can be measured with high precision and is defined to be exactly 2.99792458×108 meters/second. Thus the speed of light is a legislated quantity.

        The second - to measure time. The second is defined to be that required for 9,192,631,770 cycles of a cesium (atomic) clock. This time is very close to that of the "mean solar day" divided by 24×60×60. Small time intervals are measured in milliseconds (10-3 seconds), microseconds (10-6 seconds), nanoseconds (10-9 seconds) and a host of other
prefixes are used .
        (It is of interest to note that in 1 nanosecond light travels approximately one third of a meter. As most small computers today have CPU rates in the order of one gigahertz (1×109 clock cycles per second), this means that during one computer clock cycle - essentially the time to perform one basic operation - any part of the computer that is more than 33 centimeters away cannot be aware of the operation. It is important to make computers small for more than concerns for cost and convenience.

          The Kilogram – to measure “the quantity of matter” (to quote Newton). The standard kilogram is defined as having the mass of a cube of water measuring 10 cm. on a side. This amount of water is represented by a platinum-iridium cylinder kept near Paris, France. The cylinder is now defined to be the standard kilogram, so the water equivalent is now a historical artifact. Copies of the standard are held by most countries and are used to reproduce and calibrate other copies. The U.S. copy arrived from France in 1890 and is kept in a vault at the NIST in Boulder, CO.

For some more on measurements click here.