(DA) Sept 21: SI System & Percent Error

Prefixes Used with SI Units

• We can put a prefix in front of the unit and change the power of it

         ^{- tera (T) 10^12
         - giga (G) 10^9
         - mega (M) 10^6
         - kilo (K) 10^3
         - hecto (h) 10^2
         - deca (da) 10^1
SI Prefixes}

• The SI System uses many prefixes to represent very large or very small numbers
  - deci (d) 10^-1
  - centi (c) 10^-2
  - milli (m) 10^-3
  - micro (µ) 10^-6
  - nano (n) 10^-9
  - pico (p) 10^-12
  - fempto (fm) 10^-15

^{***Don't use scientific notation and prefixes together! IT BECOMES VERY CONFUSING.
Experimental Accuracy}

• In general, the maximum accuracy of any measurement is half of the smallest division of the measuring device
• A ruler with measurements of millimeters has a meximum accuracy of +/- 0.5mm
• The odometer in a car has a maximum accuracy of +/- 50m.

EXAMPLE:

• A graduated cylinder has units of 1.0 mL. The accuracy of the cylinder is +/-0.5mL
• Liquid in a graduated cylinder will typically form a curved top called a meniscus
• The volume is taken at the bottom of the cylinder

The curved top is called a Meniscus

Expressing Error

• Error is a fundemental part of science
• There are usually 3 reasons of error
  1) Physical errors in the measuring device
  2) 'Sloppy' measuring
  3) Changing ambient conditions
  

Calculating Error

• Two different possibilities
  
  1) Absolute Error
           - Measured value minus accepted value
           - Absolute Error = Measured - Accepted
  
  2) Percentage Error
           - Most common
           - Percent Error = Absolute Error / Accepted Value
      
        |  Measured - Accepted |
  % = |           Accepted           | x100