Investigating Pendulums: Calculating the Effect of Mass, Length, and Angular Displacement on Period
Summary
In this physics lab activity students investigate how mass, length and angular displacement affect the period of a simple pendulum. Students control variables, testing one variable at a time, using manual techniques (stopwatch, human eye, etc). Data is graphed and compared to determine what variables affect period. Acceleration of gravity is also calculated and verified. The entire lab is then repeated using Vernier LabPro and Photogate in order to compare manual results with electronic results. A summary paragraph is written by students describing the affects of variables on period and the accuracy of manual techniques versus electronic techniques.
CollapseLearning Goals
This activity is designed for students to verify length of a pendulum as the only variable affecting period and to verify the acceleration of gravity. Additionally, students will learn the importance of taking accurate measurements and how electronic equipment can aid and enhance human accuracy. Students will utilize the skills of observation, equipment operation, graphing, data analysis, critical thinking, writing, measurement, and accuracy. Key concepts are dispelling the misconception of mass affecting free fall and period of a pendulum. Other concepts include the affects of human error on accuracy and the importance of maintaining constant variables in experiments. Key vocabulary words include cycle, period, frequency, angular displacement, and center of mass.
Context for Use
This is a lab activity intended for upper high school physics students. Length of class time would be approximately five 55 minute periods or 3.5 block class periods. Vernier LabPro and Photogate are needed for part 2. Part 1 can be done alone if Vernier is not available. This would cut class time by approximately half. Students should have a basic understanding of the principle workings of a pendulum before this activity, but not detailed exposure in order to make this more inquiry based. This would be a good opening activity to Simple Harmonic Motion and or free fall-gravity.
Description and Teaching Materials
In this activity students construct a simple pendulum using thread and a weight.* Length of thread, mass size, and release angle of pendulum bob are varied through three sets of runs where two variables are held constant. Students use complete manual data collection through the first three sets of runs and then repeat the activity using Vernier LabPro and Photogate to record most data. Data is then graphed and analyzed for the six separate runs and the acceleration of gravity is calculated. Materials needed are thread, varying masses, ring stand, stopwatch, protractor, meter stick, Vernier LabPro, and Photogate. This activity will be utilized at the beginning of a unit on Simple Harmonic Motion, after students have been introduced to the basic principles of pendulum motion and how it can be used to verify the acceleration of gravity. Closure strategies will be class discussion of results ensuring that any misconceptions or findings are corrected. Included in this will be a comparison of complete manual data collection with electronic data collection. * Complete lab sheets are attached to this document. assignment handout (Microsoft Word 110kB Aug24 07)
Teaching Notes and Tips
Students should be alerted to not pull the pendulum bob back farther than 45 deg, especially when using the Photogate. Control of bob is compromised and the Photogate could be damaged if it is hit by the bob. Also, students should be made aware that above 15 deg the pendulum loses the precision of Simple Harmonic Motion and they should look for any changes in data after a displacement of 15 deg. Students need to be reminded to pay particular attention to detail and accuracy especially when retying and measuring thread length. They tend to want to rush and can get a little careless. I have never done part 2 of this activity using Vernier LabPro with Photogate for comparison.
Assessment
I act as facilitator during this activity, moving from group to group checking progress, questioning, and redirecting if necessary. If it seems a few groups are having the same difficulties I will collect the classes' attention and facilitate as a whole. The student generated graphs of data are a good indicator of their lab technique. If this lab is done accurately class results should be very close in comparison. Questioning in class and correct responses on quizzes or tests will show if students achieved the learning goals for this activity. Completed lab reports with graphs and write up will also be used to check student achievement.
Standards
I. HISTORY AND NATURE OF SCIENCE:
B. Scientific Inquiry: The student will design and conduct a scientific experiment.
Benchmarks:
2. Distinguish between qualitative and quantitative data.
4. Identify possible sources of error and their effect on results.
II. PHYSICAL SCIENCE:
C.Energy Transformations: The student will understand energy forms, transformations and transfers.
Benchmarks:
2. Differentiate between kinetic and potential energy and identify situations where kinetic energy is converted into potential energy and vice versa.
D. Motion: The student will understand the nature of force and motion.
2. Describe the effect of friction and gravity on the motion of an object.
B. Scientific Inquiry: The student will design and conduct a scientific experiment.
Benchmarks:
2. Distinguish between qualitative and quantitative data.
4. Identify possible sources of error and their effect on results.
II. PHYSICAL SCIENCE:
C.Energy Transformations: The student will understand energy forms, transformations and transfers.
Benchmarks:
2. Differentiate between kinetic and potential energy and identify situations where kinetic energy is converted into potential energy and vice versa.
D. Motion: The student will understand the nature of force and motion.
2. Describe the effect of friction and gravity on the motion of an object.