SI SYSTEM AND PERCENT ERROR: September 21, 2010

Today in class, we learned about the different units of measurements, such as common Metric Prefixes used in Chemistry.

We also learned about Experimental Accuracy. Not all experiements will result with very accurate results so we use a special symbol to show uncertainty of a measurement. A plus-or-minus symbol, ± is used.

*the menuscus is only measured on the top with certain liquids that curve that way
In the example above, the meniscus falls between 31-32. Since it is not on 31 but is less than 32 we could estimate the meniscus is about... 31.7mL. To show our uncertainty, we add ± to our measurement as follows -> 31.7 ± 0.1milliliters. This reads: "Thirty- one and seven tenths plus-or-minus one tenth milliliters."

Last but not least...
We learned about expressing ERROR

1. Error is a fundemental part of Science and there are usually 3 reasons for error:

• Physical Errors in the measuring device
• "Sloppy" measuring (i.e Being lazy and not taking proper measurements)
• Changing abient conditions

TWO DIFFERENT POSSIBILITIES:
-Absolute Error & Percentage error

Absolute Error

•  Absolute Error= Measured- Accepted
• Its measured value minus accepted value will give you absolute error.

Percent Error

• Most common
• Percent Error= Absolute/Accepted Value
• %Error= [Measured-Accepted÷Accepted] x 100

ie. 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)     than times by x100 = 14%
17.5(Accepted)

Post by Ren Flores