Using Scientific Measurements

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# Using Scientific Measurements - PowerPoint PPT Presentation

Using Scientific Measurements. Accuracy and Precision RHS Science Department. Whachathinkboutit ?. Write your definition of the following terms: Accuracy Precision Do they mean the same thing or is there a difference? If there is a difference, what is the difference? (Give an example.).

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### Using Scientific Measurements

Accuracy and Precision

RHS Science Department

Whachathinkboutit?
• Write your definition of the following terms:
• Accuracy
• Precision
• Do they mean the same thing or is there a difference?
• If there is a difference, what is the difference? (Give an example.)
Accuracy vs. Precision
• To most people, the words Accuracy and Precision are synonymous.
• In the field of science, they have quiet distinct meanings.
• Accuracy is defined as the closeness of the measurement to the correct or accepted value of the quantity measured.
• Precision is defined as the closeness of a set of measurements of the same quantity to one another.
Application of Concept
• Who is more accurate when measuring a book that has a true length of 17.0cm?

Susan:

17.0cm, 16.0cm, 18.0cm, 15.0cm

Amy:

15.5cm, 15.0cm, 15.2cm, 15.3cm

Application of Concept

Who is more precise when measuring the same 17.0cm book?

Susan:

17.0cm, 16.0cm, 18.0cm, 15.0cm

Amy:

15.5cm, 15.0cm, 15.2cm, 15.3cm

Error
• Due to a variety of factors (eyesight, equipment limitations, material, etc…) there is a margin of error between our experimental measurement value and the accepted value.
• To calculate the error, we apply the following formula:

Error = Valueexperimental - Valueaccepted

Percentage Error
• The amount of error is generally expressed as a percentage of the accepted value.
• To calculate percent error, we apply the following formula:
Practice
• A student measures the mass and volume of a substance and calculates its density as 1.40 g/mL. The correct value of the density is 1.30 g/mL. What is the percentage error of the student’s measurement?
• G.U.E.S.S
• Given (measured = 1.40 g/mL; correct = 1.30 g/mL)
• Unknown (percent error)
• Equation ( )
• Substitute ()
• Solve (7.7%)
Interpreting the Results
• Percent error can be positive or negative.
• If it has a positive value, it means that the experimental or measured value was greater than the accepted value.
• If it has a negative value, it means that the experimental or measured value was less than the accepted value.