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Chapter 2 - Physical Science Methods
A standard of measurement is an exact quantity that people agree to use as a basis of comparison.
When a standard of measurement is established, all measurements are compared to the exact same quantity - the standard.
In SI (the metric system), prefixes are used to make the base units larger or smaller by powers of ten.  The most common prefixes are:
   kilo- ... 1000 times
   deci- ... one tenth
   centi- ... one hundredth
   milli- ... one thousandth
   micro- ... one millionth
   nano- ... one billiionth

The most commonly used SI units are: length=meter, volume=liter (cubic decimeter), mass=kilogram, time=second, temperature=Kelvin.
Any SI unit can be converted to any other related SI unit by multiplying or dividing by the appropriate multiple of ten.
Density is the mass per unit volume of a material.
Zero degrees Kelvin is absolute zero.  273 degrees Kelvin is 0 degrees Celsius ... the freezing point of water.  So, K=C+273.

Graphs are visual displays of information or data.
Line graphs show continuous changes between related variables.  Bar graphs are used toshow data collected by counting.  Circle or pie graphs show how a fixed quantity can be broken into parts.
In a line graph, the independent variable is always plotted on the horizontal x-axis; the dependent variable is always plotted on the vertical y-axis.

There are many benefits and drawbacks to the adoption of SI.
SI units are already in wide use on consumer goods in the U.S.