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×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×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 (seconds), microseconds (seconds), nanoseconds (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×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