Last year, a news article in The Science Teacher titled “Cobra’s Aim” described how a researcher analyzed snake-venom trajectories using the capabilities of high-speed photography (2005). Analyzing real motion with frame-by-frame precision can also be conducted using modestly priced digital-video camcorders. Although well below the 1,000 frames-per-second threshold of high-speed cameras, commercially available camcorders grab 30 frames per second (see “Determining frames per second”). A replay dissected at this lower frequency is fun to watch, challenges students’ perceptions, and unleashes new instructional possibilities for motion, momentum, and energy.

One digital-video–based investigation uses falling dominoes to develop students’ inquiry skills. Analyzing toppling dominoes in slow motion sharpens students’ observations of a fairly common childhood experience and stimulates creativity for subsequent explorations within the field of mechanics. With student participation as the centerpiece, the activities described in this article show how inquiry skills are developed, formalized, and extended using camcorder technology.

Exploring motion

The classroom digital-video introduction can occur as students explore the topic of motion in physics. To prepare the equipment and students’ understanding of the camcorder’s role in their scientific inquiry, the teacher inserts the camcorder’s stereo-video cable into its AV port and connects the colored end(s) of this cable to the respective In/Out port(s) on a data projector or television.

The teacher begins video recording the classroom so students instantaneously see the camcorder’s field of view and instructs students to slowly rise from their chairs and then sit back down. As students stand in unison, the teacher videotapes their rise-and-sit motion. The replay captures the fundamental power of camcorder technology as the teacher replays students’ stand-and-sit action using the frame-advance feature (a button found on the camcorder’s remote control). One push or click of this button unfolds the students’ motion with increments lasting one-thirtieth-of-a-second. The teacher poses the following questions to check student understanding of the replay:

• How many clicks (button pushes) on the controller does it take to view one second of real-time motion? Explain.
• If 10 clicks are pushed, how much real time elapsed? Explain.

Next, the class focuses on one student shown clearly in the replay, for instance, Juan. The teacher asks students to notice Juan and whether is it possible to calculate Juan’s rate of standing up with this technology? Why or why not?

A class discussion focuses on what is needed to determine the speed of a moving object—distance and time. The teacher then brings Juan a meterstick and positions it on his desk so the stick’s orientation is perpendicular with respect to the floor. The teacher asks students “If Juan stands up while being video recorded could his rate of standing up be calculated? Explain.”

The teacher videotapes Juan’s motion and replays the tape. Using a laser pointer (being careful not to shine it in students’ eyes), the teacher zeros in on the edge of Juan’s shoulder and creates a reference point for the class demonstration. One click of the remote control reveals Juan’s shoulder has moved 0.02 m when judged against the meter-stick reference. The teacher asks students:

• How much real time elapsed with one click of the remote control?
• How far has Juan’s shoulder moved during that interval of time?

Now knowing distance and associated time, students calculate Juan’s rate of ascent in meters per second. With their calculation finished, students explain in writing how the digital camcorder, combined with a well-placed measuring tool, enables them to determine the speed of an object. A purposeful exchange between students closes this section as they trade, read, and score their neighbor’s answer based on its clarity (A, B, C, D, or F). The peer-to-peer review is a formative assessment because students give timely feedback, and by doing so they collectively demystify how the camcorder and measuring device mimic police radar. After returning their peers’ papers, a few students share their explanations orally before the class begins the Digital Dominoes investigation.

Investigating dominoes

Materials needed for the Digital Dominoes investigation include a digital camcorder, remote control, stereo-video link cable, 50–70 dominoes, one metric ruler per work team, and paper copies of the Digital Dominoes investigation (Figure 1).

To begin, the teacher selects seven dominoes to arrange in a linear fashion on top of a table so all students have an unobstructed view. The teacher then pushes the first domino forward so the remaining six topple. The rapid-ratchetlike sound focuses the class’s attention as they listen to the two purposes of this investigation:

• Purpose #1: Discover the linear (linelike) arrangement to make seven dominoes fall at the slowest possible speed.
• Purpose #2: Design and conduct a scientific investigation using dominoes.

The teacher distributes copies of the Digital Dominoes investigation and together the class discusses problems one and two before students retrieve the materials, seven dominoes and a ruler, and begin collaborative work. The work teams use 20 minutes to design, investigate, and discover better or best solutions before videotaping their final answers. On a practical note, to identify anonymous dominoes during the replay, students should write their names on a piece of scratch paper to place next to their arrangement. The teacher should not videotape any student faces and students should return all materials before the slow-motion replays are analyzed.

Analysis of the investigation formally begins as students sketch a side profile of each team’s arrangement, calculate the speed of the toppling sequences, and make ongoing inferences about better solutions based on these quantitative results. The active learning session ends with students finishing the Digital Dominoes investigation worksheet (Figure 1). An answer key developed with student cooperation on the next day is the second, instructionally supportive assessment and reviews the purposes of the investigation.

Building student inquiry

Once students grasp how the frame-advance feature works, replays from the camcorder help them untangle other topics within mechanics. The teacher should point out to students the video camera’s limitations before students launch their inquiry-propelled investigations. The camcorder captures top speeds of 3 m/s, and recognizes decimeter divisions on a meterstick recorded from 4 m away. The following investigation illustrates these limits, investigates Newton’s first
law of motion, and offers an introductory look at projectile motion.

Figure 2. Investigating Newton's first law of motion.

The activity involves a toy action figure shown resting on the windshield of a remote-control car and a barrier made of two bricks (Figure 2). The sandwiched-together bricks stop the speeding car but not the toy action figure. The two metersticks—one resting horizontally and one standing vertically—provide the distance backdrop for analyzing the car’s speed and the toy action figure’s horizontal and vertical speed. Replays that show the car smashing into the bricks at higher speeds become too blurry for analysis, so capturing motion within the 3 m/s parameter keeps students’ subsequent investigations and replays purposeful. This camcorder remote-control-powered scenario impacts student learning significantly better than prior efforts obtained from overhead transparencies.

A driving force behind classroom use of camcorder technology is to significantly impact student learning. For science instruction, that must include strengthening inquiry-based attitudes—the camcorder introduction, domino investigation, and Newton’s first law investigation are sequentially structured to excite inquiry-propelled learning.

These activities follow a constructivist approach because students naturally promote their own interests, and, at times, create extremely funny scenarios unmatched by textbook resources.

The following topics easily combine student curiosity and camcorder technology to produce rich moments of learning: balanced forces, kinetic energy, the conservation of mechanical energy, momentum, and the conservation of momentum. I have successfully used the digital video to show the acceleration of dropped balls from rest and carts down an incline. My students also verified Newton’s first law by recording a penny staying at rest as an index card is flicked away underneath it. The first law replay elevated a routine activity into a significant learning moment because prior to digital video, students never witnessed inertia unfold slowly. An additional minute for the visual replay gave students time to process the first law.

Digital video technology is a dynamic and affordable tool to launch and sustain students’ scientific inquiry skills, and adds a thrilling dimension to learning. . . almost as dramatic as spitting cobras.

Bruce Kelly (bkelly@esd113.k12.wa.us) is a secondary science and math content specialist at ESD 113, 601 McPhee Road, Southwest, Olympia, WA 98502.

Reference

The Science Teacher. 2005. Headline science: Cobra’s aim. The Science Teacher 72(4): 14.