This was published in the Talkin’ Physics column of The Physics Teacher’s October 2017 issue.
End-of-the-chapter textbook problems are often the bread-and-butter of any traditional physics classroom. However, research strongly suggests that students be given the opportunity to apply their knowledge in multiple contexts as well as be provided with opportunities to do the process of science through laboratory experiences (Mestre, 2001). Little correlation has been shown linking the number of textbook problems solved with conceptual understanding of topics in mechanics (Kim & Pak, 2002). Furthermore, textbook problems as the primary source of practice for students robs them of the joy and productive struggle of learning how to think like an experimental physicist. Methods such as Modeling Instruction tackle this problem head-on by starting each instructional unit with an inquiry-based lab aimed at establishing the important concepts and equations for the unit, and this article will discuss ideas and experiences for how to carry that philosophy throughout a unit.
Practicums, practicums, practicums!
Designing the right kind of lab experience is more than simply having students make calculations based on making real measurements. What makes a lab experience a practicum is that the calculation students make is verifiable. An experiment should be able to be carried out that undeniably shows, either through visual confirmation or an additional measurement, that their prediction is accurate or not. This allows nature to be the arbiter of the quality and accuracy of their work instead of the teacher, thus placing students in an environment far more representative of how real science actually works.
Through lab practicums, students also get to see the importance of measurement uncertainty and significant figures. If in a multi-step calculation a student rounds their results in between each calculation, their final prediction is likely to greatly deviate from reality regardless of the quality of their solution or initial measurements. The same applies for poor measurement techniques in that an accurate analytic solution is worthless for predictions if the measurements are taken poorly. Practicums also emphasize that equations are not black boxes that take in numbers and magically eject answers, but instead are mathematical models that provide predictions (accurate or otherwise) for how the world works.
Lab practicums can be as simple or as complicated as they need to be for the desired level of rigor or available time. After students have begun tackling the concepts of constant velocity, instead of assigning them problems of the A car drives at a constant velocity of…variety, why not instead give them a constant-velocity tumble buggy and have them make predictions about its motion ? Have them calculate the velocity and then place a piece of tape on the floor where they predict the buggy will be after some amount of time determined by the teacher. If more pressed for time, calculate the velocity beforehand and provide that to students. For an added challenge, provide students two buggies with different velocities and ask them to place tape on the floor where the two will collide.
For calculus-based classes, have students use a large rubber band to launch a wooden block across the floor and predict where on the floor the block will skid to a stop. They will need to model the non-linear force-position function for the rubber band to figure out the initial amount of elastic potential energy that is then transferred to kinetic energy in the block and thermal energy due to the friction between the block and the floor.
Accurate time measurements for experiments like this are often difficult to achieve. However, a free mobile app called Hudl Technique, on both Android and iOS, takes not only slow-motion video, but also provides accurate time measurements down to the hundredth of a second. This opens the door for experiments for virtually all topics within mechanics at whatever level of challenge desired.
For statics problems hang objects from multiple spring scales all pulling on an object from different angles. Give students the mass of the object and have them predict a reading on a scale or vice-versa.
For energy, use two spring scales with different k-values that are tied to low-friction carts along a string. Task students with figuring out how far to stretch each spring such that the carts have the same velocity (O’Shea, 2012).
Once thinking has been shifted towards lab practicums, an entire new world of practicing physics in the literal sense is opened up. But even in the face of time and equipment limitations, there are Direct Measurement Videos (DMV). The Science Education Resource Center (SERC) at Carlton College has a series of high-quality slow motion videos of different experiments relevant for a variety of physics topics, primarily mechanics. What sets these apart is that students can use the DMV web player to advance movies frame-by-frame as well as use screen overlays to take time and position measurements directly from the videos. They work seamlessly on laptops, desktops, and mobile devices.
What ties all of this together is the attempt to provide students with as authentic a scientific experience as possible. Real scientists solve new problems every day without an authority figure, other than nature itself, to appeal to when things get tough. They must deal with all kinds of problems associated with accurate data collection, reliable experimental setups, and finicky equipment. The end product of an experiment is rarely what it started out as, and allowing students a variety of opportunities to experience that process, to do science, will provide them with the kind of problem solving skills that physics teachers claim as the benefits of studying physics.
Kim, E., & Pak, S.-J. (2002). Students do not overcome conceptual difficulties after solving 1000 traditional problems. American Journal of Physics, 70(6), 759.
Mestre, J. P. (2001). Implications of research on learning for the education of prospective science and physics teachers. Physics Education, 36(1), 44.
O’Shea, K. (2012, February 5). Building the Energy Transfer Model. Retrieved from Physics! Blog!: https://kellyoshea.blog/2012/02/05/building-the-energy-transfer-model/