It is important to be able to MAKE measurements and to decide whether a measurement is CORRECT.

-- Are you “certain” that your measurement is correct? HOW “certain” are you???

2.32.344 gg

A measurement is a quantity that has both a number and a unit.

36.36.11 mLmL 16.5 16.5 Years OldYears Old

Accuracy, Precision, and Error

Here is an example:Here is an example:

How old is this cat?How old is this cat?

_____ Months_____ Months (everyone must guess)(everyone must guess)

How do you evaluate accuracy and precision? (Your thoughts???)

• Accuracy is a measure of how close a measurement comes to the actual or true value of whatever is measured. (closest to TRUE Value)

• Precision is a measure of how close a series of measurements are to one another. (repeated Save Value)

Accuracy and Precision

Who was more ACCURATE and more PRECISE in your measurements of the age of my cat?

AccuracyAccuracy – closest to TRUE Value – closest to TRUE ValuePrecisionPrecision – repeated Same Value – repeated Same Value

Determining Error

• The experimental value (EV) is the value measured in the lab. (by the student)

• The accepted value (AV) is the correct value based on reliable references.

• The error is the difference between the experimental value and the accepted value

Error = experimental value (EV) - accepted value (AV) (measured by student) - (correct value)

What is the error in your measurement of the age of my cat?

The percent error is an absolute valueabsolute value (there is no positive or negative value.)

Percent Error

Percent Error = x 100% EV - AVAV

What is the percent error in your measurement of the age of my cat?

Error VS Percent ErrorWhat is Mr. Pearson’s weight? Experimental Value (EV) = 115 kgActual Value (AV) = 110 kg

= 115 kg – 110 kg x 100 % = 4.5%

Error = EV – AV

Percent Error = x 100% EV - AVAV

= 115 kg – 110 kg = 5 kg

110 kg

Error VS Percent ErrorWhat is the weight of my car? Experimental Value (EV) = 3,585 kgActual Value (AV) = 3,580 kg

= 3,585 kg – 3,580 kg x 100 % = 0.14%

Error = EV – AV

Percent Error = x 100% EV - AVAV

= 3,585 kg – 3,580 kg = 5 kg

3,580 kg

What is Mr. Pearson’s weight? Error VS Percent Error

What is the weight of my car? Error = 3,585 kg – 3,580 kg = 5 kg % Error = 3,585 kg – 3,580 kg x 100 % = 0.14%

3,580 kg

% Error = 115 kg – 110 kg x 100 % = 4.5% Error = 115 kg – 110 kg = 5 kg

110 kg