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SI System & Percent Error
Wednesday, September 22, 2010 /6:30 PM

SI System & Percent Error


Today, we learned about the SI System and Percent Error. Mr. Doktor showed us a video on youtube about the powers of ten.


http://www.youtube.com/watch?v=aPm3QVKlBJg

PREFIXES USED WITH SI UNITS AND SI PREFIXES

We learned that we can put a prefix in front of the unit and change the power of it. The SI system uses many prefixes to represent very large or very small numbers.

TERA -----(T)~~~~10^12
HECTO---(h)~~~~10^2
GIGA------(G)~~~10^9
DECA-----(da)~~10^1
MEGA----(M)~~~10^6
KILO-----(k)~~~~10^3
DECI -----(d)~~~~10^-1
CENTI---(c)~~~~10^-2
MILLI------(m)~~~10^-3
MICRO-----(u)~~10^-6
NANO----(n)~~~10^-9
PICO-----(p)~~~~10^-12FEMTO-----(fm)~~~~10^-15


* REMEMBER!!! DON'T use scientific notation and prefixes together! It becomes VERY confusing. 


We also learned about Experimental Accuracy, that not all measurements are accurate. Any measurement are usually half of the smallest division of the measuring device. We use a plus-or-minus symbol, ± instead. A graduated cylinder has units of 1.0mL. The accuracy of the cylinder is ±0.5mL. As Mr. Doktor showed us in class, when he added water in the graduated cylinder, the water formed a curved top called a meniscus. The volume is taken at the bottom of a meniscus. 


Lastly, we were taught about expression error, absolute error and percent error.


Error is a fundemental part of Science which there are usually 3 reasons for error.
1) Physical Errors in the measuring device
2) "Sloppy" measuring [like not measure correctly]
3) Changing abient conditions
There are two different possibilites, absolute error and percentage error.


ABSOLUTE ERROR
~measured value minus accepted value
Absolute Error= Measured- Accepted


PERCENTAGE ERROR
Its the most common error.
~Percent Error= Absolute/Accepted Value
%Error= (Measured-Accepted) x 100
                     Accepted
AN EXAMPLE MR.DOKTOR gave us was:
You measure the weight of an orange to be 15 N. The actual weight is 17.5 N. What is the percent error?
(15[measured]-17.5[accepted]) x100 = 14%
17.5[accepted]