Direct Measurement Videos > Activities > Direct Measurement Video Analysis - Blow-Dart Collides With Cart

Direct Measurement Video Analysis - Blow-Dart Collides With Cart

Compiled by Carrie Williams. Video by Peter Bohacek.
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This activity will allow students to analyze a direct measurement video clip of a blow dart colliding with a cart initially at rest. Students will be able to make measurements directly from the video that will allow them to investigate physics concepts such as velocity and conservation of momentum.

- NOTE -

This activity refers to a video that is no longer freely available. The content of this activity is here for reference and can be adapted for other videos, or for a live classroom demo or hands-on lab.

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Learning Goals

  • Students will be able to use a video to measure the velocity of the dart and cart, before and after the collision.
  • Students will be able to compare momentum before and after a collision.
  • Students will become more familiar with using videos to directly measure physics concepts.
  • Students will apply conservation of momentum to a real-world situation.

Context for Use

This lesson is set up to introduce direct measurement videos. This activity should take about one 50 minute class time from introduction of material to the end of analyzing. The students should be familiar with basic physics concepts such as how to measure velocity, acceleration, and momentum mathematically. Generally, this would be useful for any introductory physics course. Using the video clip should encourage critical thinking. This lesson is based on showing how to use the video direct measurement for the first time. The teacher can give as much detail in the instructions as he/she wants, or be vague and give only the necessary numbers for calculations and let the students find the measurements on their own by trial and error. This activity has the capability of being used for direct instruction or inquiry based learning.

Description and Teaching Materials

  • Each student will need a computer to play the video on in order to analyze it. If there are not enough lap tops available, then the students may work in groups.
  • This activity uses the Direct Measurement Video, Blow dart collides with cart. (This video is no longer freely available.) Students can access videos via the student video library which allows access to all videos for students, without links to instructor materials.
  • Students will need to perform calculations so scratch paper, pencil, and calculator are useful.
  • The following sheet can be handed out to the students to help keep them organized and provide questions for them to answer: Student Handout (Microsoft Word 28kB Jul13 12)
    • In order to change the difficulty level of this lesson simply take out the questions that lead up to how to calculate the conservation of momentum and ask only questions 5-8.
  • Here is an answer key for the student handout: Handout Answer Key (Microsoft Word 29kB Jul13 12)

Teaching Notes and Tips

If a teacher plans to teach this lesson as an inquiry based lesson, it may be beneficial to have students in groups in order to facilitate questions and discussions.

This is set up to introduce direct measurement videos, so the first time the students see them they should be given time to play around with how the measurements could be found and how to use the frame counter or go frame by frame. The lesson may end up taking more than one class period depending on the knowledge of video software and background knowledge and comfort of physics equations needed.


Ongoing assessment will have to be done by the teacher while the students are working on analyzing the video clip. When the students are stuck on a question that they are being asked, the teacher can break the question down into other questions instead of simply explaining directly how to answer the initial question. The teacher can then assess if the students are stuck on the question being asked or if they are not understanding the process being asked. They will have to hand in some written answers to questions in order to show they fully understood what was being asked and how to play the video frame by frame in order to analyze everything properly. Once the students understand process of analyzing video, more difficult questions can be asked about other videos. Assessing the process of actually analyzing the video should be done on the first or second video the students see to ensure they can be more independent and do more inquiry with later videos they are asked to analyze. Since this is more of an inquiry based and non-standard questioning technique, to check for understanding, textbook questions may be given as homework to answer similar questions that were asked in the direct measurement video here.

References and Resources

Student Handout (Microsoft Word 28kB Jul13 12)

Handout Answer Key (Microsoft Word 29kB Jul13 12)

Extra questions with answers