Hanging-out with Galileo
Summary
In this physics lab, students isolate the factors that determine the period of a pendulum. The students test hypotheses and also do a data match to see if their experimental results come close to the mathematical results. Students will also learn a little something about Galileo.
CollapseLearning Goals
The students should learn how string length effects pendulum periods, and they should learn the equation that describes this. They will do observations, data collecting, hypothesizing, and data analysis. Key words should include: pendulum, period, length, and acceleration of gravity.
Context for Use
This activity works well in a class of 20 or fewer, with an hour time, and in a place where you can hang string and ornaments from the ceiling or tables. The students should already be familiar with g (acceleration due to gravity). This is a rather low-tech and low-budget activity.
Description and Teaching Materials
Materials: A heavy holiday tree ornament and a light weight one. Lengths of string. Stopwatches. Graph or table paper.
Before doing this experiment, the teacher should read out-loud some sections from "Galileo and the Scientific Revolution" ISBN 0-486-43226-2 (pages 17 - 19) to the students. This will set the tone. Perhaps even some pictures of Pisa and Italy would help the students get in to the mindset.
After explain what Galileo was trying to determine (period of a pendulum), have the students hypothesize about what would swing faster - a light ornament or a heavy one. Give each group of 2 to 4 students two identical lengths of string - and two different weight ornaments. Have them attach the ornaments to a chemistry O-ring stand, or have them hang them off of tables or the ceiling. Tell the students to release the pendulums at the same time, and see which one gets to 4 swings first. The students should also time these swings - and take an average (by dividing the 4 swing time by 4) to get the period.
Have the students compare times, and then have them swap string lengths with a nearby group. They will compare results, and the teacher will reconvene class and lead them in a guided discussion as they try to get to the conclusion that: 1. Same length strings will give you same periods. 2. Weight of ornament doesn't matter, unless, 3. The air friction slows the lighter one down more. The teacher should also introduce the equation T = 2pi*sqrt(l/g) - and have the students do a data match - to see if their time results, and the string lengths, match with what the equation gives them.
This is an easy experiment, and it mimics what Galileo did to determine pendulum properties.
Before doing this experiment, the teacher should read out-loud some sections from "Galileo and the Scientific Revolution" ISBN 0-486-43226-2 (pages 17 - 19) to the students. This will set the tone. Perhaps even some pictures of Pisa and Italy would help the students get in to the mindset.
After explain what Galileo was trying to determine (period of a pendulum), have the students hypothesize about what would swing faster - a light ornament or a heavy one. Give each group of 2 to 4 students two identical lengths of string - and two different weight ornaments. Have them attach the ornaments to a chemistry O-ring stand, or have them hang them off of tables or the ceiling. Tell the students to release the pendulums at the same time, and see which one gets to 4 swings first. The students should also time these swings - and take an average (by dividing the 4 swing time by 4) to get the period.
Have the students compare times, and then have them swap string lengths with a nearby group. They will compare results, and the teacher will reconvene class and lead them in a guided discussion as they try to get to the conclusion that: 1. Same length strings will give you same periods. 2. Weight of ornament doesn't matter, unless, 3. The air friction slows the lighter one down more. The teacher should also introduce the equation T = 2pi*sqrt(l/g) - and have the students do a data match - to see if their time results, and the string lengths, match with what the equation gives them.
This is an easy experiment, and it mimics what Galileo did to determine pendulum properties.
Teaching Notes and Tips
You might want to have the students just rotate from station to station - each has different length of strings.
You might also want to train the students on using the stopwatches.
You might also want to train the students on using the stopwatches.
Assessment
Each student should have a graph paper where they recorded the data from the lab, and the numbers from the equation. The teacher could easily turn this in to a lab report and have the student turn it in the next day. There should be a conclusion section in the lab report that explains what string length does to period.
Standards
MN 9-12 I. D. 1 - Science History
MN 9-12 II. D. 2 - Effects of gravity and friction on motion.
MN 9-12 II. D. 2 - Effects of gravity and friction on motion.