Scientific Measurement: Reviewing precision vs. accuracy, Measurement, and Significant Figures
Summary
In this introductory physics lab, students will review scientific measurement concepts that should have been covered in previous science classes. The concepts of precision and accuracy will be compared and contrasted, along with a discussion of measuring to the proper precision as dictated by a specific measuring device. Significant figures/digits (sigfigs or SDs) will also be reviewed, with a discussion about why it is necessary to use sigfigs in measurements and calculations, and a review of the rules for using proper significant figures. After a "pen and paper" review of these concepts, students will develop a procedure, in which they will use the concepts of proper precision in measurement and significant figures, to determine the density of a marble.
CollapseLearning Goals
The purpose of this lab is to:
· differentiate between precision and accuracy
· practice using various laboratory measuring techniques
· read scales on various laboratory instruments to the proper precision
· calculate values from data gathered, using the proper number of significant digits in the final answer
· differentiate between precision and accuracy
· practice using various laboratory measuring techniques
· read scales on various laboratory instruments to the proper precision
· calculate values from data gathered, using the proper number of significant digits in the final answer
Context for Use
This lab was designed to be used at the beginning (it was the first lab completed, at the end of the first week of school) of a general/introductory high school physics class. All of the students in the class were 12th graders and had taken chemistry the previous year. The school in which this lab was used had identified that their science program was weak and was making an effort to raise the standards for students throughout the high school. Students should have used significant figures throughout their chemistry class the previous year, however I found that my particular students had very little understanding of proper precision in measuring, using significant figures, and designing an experiment. Therefore this lab became more of a teaching tool than a review tool (it was my first year in this school so I spent the first few classes determining the incoming level of my students). This lab (minus the extensive pre-lab work) could also be used as a lab practical at the end of a measurement unit in a physical science or chemistry class.
Description and Teaching Materials
This activity starts out with a fairly extensive review of density measurements, accuracy vs. precision, precision in measurements, and significant figures. Students read background information and answered questions on each of these topics as homework the day before the lab was completed in class. Students were also asked to brainstorm ideas about measuring mass and volume before coming to class to complete the lab. The day of the lab began with a quick discussion about the previous night's homework, specifically focusing on their ideas for measuring mass and volume. After making sure the students were on the right track with their procedures, a blank data table was handed out and they were put into pairs to complete the lab. At the conclusion of the lab students should have:
· Used two different tools for measuring mass of a marble (triple beam balance and electronic scale)
· Used two different methods for measuring volume of a marble (immerse in water and measure diameter to calculate using the formula for the volume of a sphere)
· Calculate density
· Calculate percent of error from the known density of glass (density of glass = 2.6g/cm3)
This activity was specifically designed to use very little equipment (perfect for those schools that don't have a lot of equipment). If only one type of scale is available, students only need to measure mass using one method. Other objects of pure substance can be used (brass - density 8.47g/cm3, aluminum - density 2.64g/cm3, copper - density 8.94g/cm3, steel - 7.86g/cm3), but marbles are cheap and easy to come by!
Students will answer some analysis questions at the conclusion of the lab and the day after completing the lab we will have a discussion in class about the scientific method and possible sources of error in this particular lab. Pre-Lab (Acrobat (PDF) 44kB Sep18 08) Data Tables and Analysis Questions (Acrobat (PDF) 19kB Sep18 08)
· Used two different tools for measuring mass of a marble (triple beam balance and electronic scale)
· Used two different methods for measuring volume of a marble (immerse in water and measure diameter to calculate using the formula for the volume of a sphere)
· Calculate density
· Calculate percent of error from the known density of glass (density of glass = 2.6g/cm3)
This activity was specifically designed to use very little equipment (perfect for those schools that don't have a lot of equipment). If only one type of scale is available, students only need to measure mass using one method. Other objects of pure substance can be used (brass - density 8.47g/cm3, aluminum - density 2.64g/cm3, copper - density 8.94g/cm3, steel - 7.86g/cm3), but marbles are cheap and easy to come by!
Students will answer some analysis questions at the conclusion of the lab and the day after completing the lab we will have a discussion in class about the scientific method and possible sources of error in this particular lab. Pre-Lab (Acrobat (PDF) 44kB Sep18 08) Data Tables and Analysis Questions (Acrobat (PDF) 19kB Sep18 08)
Teaching Notes and Tips
Assessment
Students will be assessed four ways:
· Evaluate pre-lab work for correct answers (see attachment)
· Observe students as they are completing the lab - look for independence, proper scientific methodology, proper use of laboratory equipment, cooperation and collaboration within the group
· Participation in the post-lab discussion
· Evaluate analysis for correct calculations and insight into potential sources of error (see attachment)
· Evaluate pre-lab work for correct answers (see attachment)
· Observe students as they are completing the lab - look for independence, proper scientific methodology, proper use of laboratory equipment, cooperation and collaboration within the group
· Participation in the post-lab discussion
· Evaluate analysis for correct calculations and insight into potential sources of error (see attachment)
Standards
Grade Level: 9-12
Strand: HISTORY AND NATURE OF SCIENCE
Sub-Strand: Scientific Inquiry.
Standard: The student will design and conduct a scientific experiment
Benchmarks:
The student will apply mathematics and models to analyze data and support conclusions.
The student will identify possible sources of error and their effects on results.
Strand: HISTORY AND NATURE OF SCIENCE
Sub-Strand: Scientific Inquiry.
Standard: The student will design and conduct a scientific experiment
Benchmarks:
The student will apply mathematics and models to analyze data and support conclusions.
The student will identify possible sources of error and their effects on results.