Online vs live physics demonstrations: does it make a difference?

Title: Comparing the effectiveness of online versus live lecture demonstrations

Authors: Greg Kestin, Kelly Miller, Logan S. McCarty, Kristina Callaghan, Louis Deslauriers

First author’s institution: Harvard University

Journal: Physical Review Physics Education Research 16, 013101 (2020)

Demos were one of my favorite parts of physics class. I remember one centripetal force demo where the instructor swung a bucket of water around his head, showing the water didn’t spill until he stopped swinging it. At that point, the water came crashing done, soaking all of his clothes.

While demos can be fun, they may not be as effective as we think in promoting student learning and can instead lead to increased confusion. For example, the students may not pay attention to what the instructor intended or may misinterpret what the demo shows . After all, demos are only effective if the students make the correct observations, which can be especially challenging for novice physics learners.

In addition to possible issues on the learning side, demos can present many practical challenges. For example, many demos require specialized equipment or set-ups that can limit how many demos can be purchased, how many demos can be done in class, or even whether there is space for the demos. Further, many introductory physics classes where demos are typically done are taught in large lecture halls, which can make viewing the demos difficult for all students.

To remedy some of these issues, the authors of today’s paper suggested performing some demos virtually instead of live. By doing video demos, most of the practical limitations are removed and annotations and animation can direct students’ attention to the relevant features of the demonstration. When swapping a live demonstration for a video demonstration, the authors found that students enjoyed the demo just as much, but actually learned more.

To perform their study, the authors selected a first-semester, introductory physics course at Harvard University with 110 enrolled students. The authors then selected two demonstrations during the semester to convert to videos. The first demo was the “shoot the monkey” demo where a projectile is aimed at a suspended stuffed monkey. When the projectile is fired, the monkey drops and the projectile strikes the monkey during its fall. (Figure 1; link to live version from Harvard)

Figure 1: Schematic of the shoot the monkey demo (Fig 2 in paper).

The second demo, which occurred a few weeks later in the class, was the “high road, load road” demo where two balls start at the same height and then race to the end of the track. One of the balls descends an additional amount (hence traveling farther but speeding up) and wins the race. (Figure 2; link to live version from NCSU)

Figure 2: Image of the high road, low road demo. (Fig 6 in paper)

The students were randomly split into two groups. The first group saw the shoot the monkey demo live and the high road, low road on video and the second group did the opposite. The instructor presenting the demonstration live followed the same script as the video and took the same amount of time (to ensure there are no effects from extra content coverage or time spent on the activity). To account for the annotations such as coordinate vectors in the video and multiple trials, the instructor performing the demonstration live wrote on the chalkboard or used wooden arrow props.

After the demo, the students wrote what they observed during the demo, rated how much they enjoyed the demo on a 1-5 scale, and answered a 5-item conceptual test about the demo.

When looking at the results, the authors found that the group of students who saw the video demo consistently performed better on the 5-item test than the group who saw the demonstrations live. In fact, the students who saw the video often did 25% better! To their surprise, the authors found that the students enjoyed the demos the same amount, regardless of how they viewed them. (Figure 3).

Figure 3: Student test scores on the post-test and student enjoyment levels. The wasn’t a difference in enjoyment based on how the students viewed the demo, but there was a difference in post-test scores. (Fig 1 in paper).

When looking at the written responses, the authors found a similar pattern. Of the students watching the high road, low road video, 63% made correct observations of the underlying physics compared to 51% of students who watched the demo live. Likewise, 88% of students who watched the shoot the monkey video made correct observations of the underlying physics compared to 57% of students who watched the demo live.

When thinking about the results, it is important to note that the videos were not simply recordings of the live demonstrations. Instead, they featured many annotations that added the trajectory, the forces, and other relevant features. In addition, the videos allowed the student to see the results of many trials. For example, the students could see that aiming above the monkey causes the projectile to miss while the students who saw the demo live had to take the instructor’s word for it.

Figure 4: Screenshots of the shoot the monkey video. (Fig 4 in paper)
Figure 5: Screenshots of the high road, low road video showing the forces acting on the lower ball. (Fig 7 in paper)

Even though this study only used one course, two demonstrations, and a short post-test, the results suggest that using video demonstrations instead of live demonstrations does not hurt student learning or enjoyment. In fact, video demonstrations may actually improve student learning. The authors note that further research is needed to see if these results generalize to other demonstrations since there may be some demonstrations which students do prefer seeing in person. Taken together, the results do not suggest that we should do away with live demos, but rather that video demos do provide the same benefits as live demos and can remove some of the challenges associated with live demonstrations.

Figures used under CC-BY 4.0. Header image from College of DuPage Flickr, used under CC-BY-2.0.

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