Direct Measurement Video of a Bouncing Ball

Peter Bohacek

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This is an activity presents an opportunity for students to practice problem solving using a direct measurement video. The video shows an inflatable rubber ball bouncing across a stage. Students make measurements from the video and calculate the velocity for the ball just as it completes the first bounce and leaves the floor on the way up.

Students will use a QuickTime video recorded at 120 frames per second, making measurements directly from the video using one given dimension and a frame-counter overlaid on the video.

The video at right is a preview of the video students use for the activity.

Learning Goals

Students will:

  • engage in open-ended problem solving to determine what quantities will be needed to solve the problem
  • make measurements from a direct measurement video
  • use kinematics and projectile motion concepts to solve the problem
  • present and defend their solution to peers

Context for Use

This activity is intended for students in an introductory physics class, either high school or college. Students should already be familiar with the projectile motion before attempting this activity. This activity is intended to be an opportunity for students to apply 2-d projectile motion concepts to a concrete and realistic example of motion.

Students can work alone, or in small groups. The instructor may want to circulate among groups, or convene the entire class for group discussion at intervals during the activity. If student have some experience analyzing direct measurement videos, this activity should take about 20 minutes.

One way to conduct this activity is for students to work in groups, writing their work on a small white board with dry-erase markers. When students have a solution, they present it to their classmates for discussion. As a class, they evaluate to solution, asking questions for clarification. If there are errors that the presenting group cannot reconcile, another group can present their solution to the class.

Description and Teaching Materials

Here is an example of questions that can guide students through this activity: Student Instructions for Direct Measurement of a Bouncing Ball (Microsoft Word 2007 (.docx) 107kB Oct24 13)

These instructions do not have a high degree of scaffolding. Students are expected to work independently, creatively, and persistently. An instructor may choose to provide hints -- but only if absolutely necessary. If students suspect that inaction will be rewarded with aid from the instructor, they may become dependent on the instructor to guide them to the solution. If absolutely necessary, ask students if they can determine ∆y for the ball during its flight. Usually, once students realize that they can, they are well on their way to a solution.

Here is the QuickTime video file: view (Quicktime Video PRIVATE FILE 4MB Oct24 13) download (Quicktime Video PRIVATE FILE 4MB Oct24 13)

If your computer does not have a QuickTime player installed, you can get one here.

Teaching Notes and Tips

Students can work individually, or in small groups with one computer per group. Alternatively, the video can be projected at the front of the class and the class can collect data (numbers of frames and distances) together, and have students solve the problem on their own.

To enable accurate measurements, the video should be downloaded to the computer and opened with a QuickTime player. Viewing the video in the browser window sometimes does not allow students to advance frame-by-frame.


This activity can be used as a formative assessment, or as practice. Summative assessment can be a traditional paper-pencil quiz using a typical projectile motion question. An alternative assessment is described in the teaching materials; students compare their calculated results to the results from a PhET projectile motion simulation. To do this, they'd configure the simulation to have the same launch velocity they calculated for the ball in the video. Students would then consider the difference between the time-airborne for the simulated projectile compared to the ball in the video.

References and Resources

The Physics Classroom website has tutorials that can help with the topics covered here: projectile motion

PhET has a simulation that allow students to explore projectile motion: projectile motion sim

Online Animated Lectures from Smart Physics has a section on 2-d motion and projectiles