The Springy Pen Lab
Lesson 7 of 10
Objective: Students will be able to prove conservation of energy in a pen's spring.
During the previous lesson, students were introduced to elastic potential energy. The goal for today's lesson is to apply that understanding of elastic potential energy in conjunction with the law of conservation of energy (HS-PS3-3) in a lab activity. Specifically, students will use pens to calculate the work done by a spring (SP5) and then explore the relationship between gravitational and elastic potential energies (SP3 & SP4). I start the class with an attention-grabbing video before moving into the actual lab activity. Today's lesson ends with an ABC summary.
This lab requires a "clicker" pen and meter stick for each lab group.
As soon as students come into the room and are seated, I play this video to pique the students' interests about springs and energy. The goal is to get students engaged by thinking about springs and energy conservation before they dive into today's lab activity. The video provides students with a great overview on the physics concepts students will need, along with a little humor. Because students are going to be active for the majority of today's class, I don't worry much about this introductory strategy being passive.
Springy Pen Lab Activity
At this point in the year my students have formed deep relationships with each other, so I allow them freedom in choosing lab partners. Groups of three seem to work best for the lab so one student can operate the stopwatch, a second can put the pen into motion, and a third student is able to record the data. After they've chosen their groups, someone from each group needs to get a copy of the lab and a pen.
The goal of this lab is to apply the work-energy theorem to a "clicker" pen. Students start by compressing the pen to the locked position, which is considered the equilibrium position. They then release then pen from equilibrium and measure the height that the pen reaches as it springs upwards. After completing ten trials to calculate the average height the pen sprung, students calculate both the spring and gravitational potential energies. By setting these energies equal to each other (and understanding the energy transformation that occurs), students solve for the spring constant, work done during compression, and the final applied force.
The procedure in the lab document is straight-forward, but I still make sure to circulate throughout the room and check-in with the groups. The first group of students who find the mass of their pens take care of zeroing the electronic balance for the rest of the class. I offer feedback on how students release their pens, ensuring they are holding the pen vertically. Students understand the expectation that once they have completed collecting the data it's time to move into the data analysis section. As I walk around, I might ask students to "Explain how energy is conserved." or "Why is the W-KE theorem applicable when you used potential energies to find the spring constant?"
When there is approximately 10 minutes prior to the end of class (5 minutes left of the time I've allowed for this activity), I ask students to put everything back the way they found it and return to their seats. I also tell them at this point that the lab is due at the start of the next class meeting. A successfully completed lab should include the data, energy transformation calculations, and a short conclusion. I also pay special attention to students' modifications that would make the pen spring to a higher height. The AP Physics 1 test emphasizes experimental design, uncertainty, and engineering practices, so this portion of the lab is critical to students' success on the AP Physics 1 exam.
In today's closure, students are each assigned a letter of the alphabet and must come up with a word that starts with that letter and pertains to the concepts covered in class today. After about thirty seconds of processing time, students share out their words with the rest of the class. I use this closure strategy when I want to do a basic check for understanding, and today students did a nice job of summarizing what was learned with their words. When I hear students contributing words such as "compress" and "mechanical energy" I see evidence of learning because those were words students needed to use to successfully complete the lab. Some of their responses were most certainly creative, such as wow and ink, but I give them credit for at least having some fun with the activity.