Absolute Uncertainty a.k.a Uncertainty

    Today we learned about a very very interesting things called.....PRECISION, ACCURACY, AND ABSOLUTE + RELATIVE UNCERTAINTY.  Notice it is in CAPS, it means that its very important.

Precision = is how reproducible a measurement is compared to other similar measurements

Accuracy = Is how close the measurement comes to the accepted or real value

(If you could use definitions then so can I)

For example if you the real value is 10 cm.  If you measured 9.7cm  then it is accurate however if it is like 50cm then its not very accurate.   If you repeatedly measure and get the results of 9.8cm, 9.8cm, 9.9cm, 9.8cm then it is precise since the results can be reproduced.  BUT if you are very bright and smarter than the average lad and measure 4cm, 9.7cm, over 9000cm then it is not precise but 9.7 is considered accurate unless you take all the numbers into account for average measurement then it is neither accurate or precise.  If you dont understand read it over 50 times. 

Then the next thing under CAPS is ABSOLUTE UNCERTAINTY.  Im absolutely sure it would mean the same thing if absolute uncertainty is uncertainty but adding absolute made it sound more scientific.  Anyway onto absolute uncertainty.  Everything that is measured IS NEVER EVER EVER EVER NEVER EVER EVER NEVER EVER EVER exact ( except things you can count like human beings though you could be half of a person but that is debatable)  There ALWAYS be a degree of some uncertainty.  And we learned how to calculate the uncertainty below. 

 If you are not bored and didnt exit out of this site then read below then exit out of the site. HF

there are 2 ways to calculate uncertainty but know this, it is always expressed in the units of measurements such as M, cm, etc and never in a ratio.

METHOD 1: THE MATH METHOD

Make measurements (the more the better) and take out any data that looks off or your sure you measured wrong then calculate the avg.  The absolute uncertainty is the greatest difference between the avg of the measurements and one of the measurements you made that are REASONABLE.

Trial                               Mass of a Swift Scout Holding 3 Mushrooms(kg)

  1                                                  20

  2                                                  19

  3                                                  20

  4                                                over 9000

  5                                                  20

First you take the most unreasonable one.  I would say the 20 but i am forced to take away over 9000 eventhough it seems most reasonable.  Then you take the average of the numbers left over.  The average is 19.75.  Then you find the greatest difference with the reasonable measurement which would be 19.75-19 = 0.75.  Then you write the answer like this.  The mass of the swift scout holding 3 mushrooms is 19.75kg plus or minus 0.75kg.  As long as the mushrooms dont blow up, your answer will be relatively correct.

METHOD 2: THE OTHER MATH WAY

 uncertainty of instruments =  Uncertianty of instruments that measure stuff

This is SUPER SUPER SUPER SUPER SUPER SUPER SUPER EASY.  You take the smallest segment on your instrument and times it by 0.1 and that is your uncertainty for the instrument.

Relative uncertainty = ABSOLUTE UNCERTAINTY/ESTIMATED MEASUREMENT

 basicly using the data you have into the formula above

it can be expressed in % or sig figs your choice.   BTW the number of sig figs indicates relative uncertainty