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Rules for Significant Figures in a Calculation Involving Addition or Subtraction Round the answer to the same number of decimal places as the number with the fewest decimal places used in the calculation.

Rules for Significant Figures in a Calculation Involving Multiplication or Division

Round the answer to the same number of significant figures as the number with the fewest significant figures used in the calculation.

Rules for Significant Figures in a Calculation Involving both Addition/Subtraction and Multiplication/Division

Do the operations in the order designated by the order of operations, rounding the digits at the intermediate steps.

Units of Measurement

In order for scientists to be able to compare their results a standard system of units was adopted internationally, known as the SI Units.  In the SI system, the basic unit of length is the meter (abbreviated as “m”), the basic unit of mass is the kilogram (abbreviated as “kg”), the basic unit of time is the second (abbreviated as “s”), and the basic unit for temperature is the Kelvin (abbreviated as “K”). Although the SI system is based on the metric system, there are some differences. In the metric system, the gram (abbreviated as “g”) rather than the kilogram is the unit of mass and the liter (abbreviated as “L”) is the unit of volume. Note that there is no basic unit of volume in the SI system. You should memorize the basic units used in both the SI system and the metric system. Length

Length is a measure of a single linear dimension of an object, usually the longest dimension. The SI unit for length is the meter, which is slightly longer than the English unit “yard”.  When measuring very long or very short lengths, it is common to use a prefix in front of the SI unit of meters for convenience.

Mass vs Weight

Mass is a measure of the amount of matter and it is the same anywhere, on earth or another planet.  Mass should be differentiated from weight, which is a measure of the gravitational force exerted by the object.  The weight of an object varies with location and depends on the force of gravity.  For example the mass of astronaut Neil Armstrong was the same on the moon as it was on earth; however, his weight on the moon was only 1/6 that of his weight on earth because the force of gravity on the moon is 1/6 that of earth.  In outer space where there is no gravitational force, an object is weightless but not massless.  We use the term weight when we actually mean mass in the lab because most of the work we do involves comparing masses measured in the same location subject to the same force of gravity.   Prefixes in the Metric System

In science, we may deal with very large or very small numbers.  For example, the number of molecules in a drop of water is a very large number while the diameter of an atom is a very small number.  In the metric system, prefixes are attached to the base units to increase or decrease the value of the base unit by factors of 10.  You must memorize the following prefixes, their symbols and meaning and be able to convert from one unit to another:  mega-, kilo-, centi-, milli-, and micro-.  The symbols and meanings for these prefixes are in Table 2.2 in your textbook on page 24, as well as in the slides, and in a separate handout in the Chapter 2 folder under Course Documents.  Keep them handy until you have them memorized!

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