Direct Measurement Videos > Activities > The "Physics Face-off" Activity

The "Physics Face-off" Activity

Peter Bohacek (
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The Physics Face-off is an activity where students use Direct Measurement Videos to learn science practices described in the Next Generation Science Standards and Advanced Placement Physics 1 and 2 curriculum. Students are assigned a Direct Measurement Video and are asked to develop a question that can be answered using the information they can glean from the video. Students try to develop a particularly difficult and interesting question that they can solve, and challenge other students to be able to solve it as well.

Unlike typical assignments where students are given the data they need and told what question to answer, students must explore to find measured data, and create a question that can be answered using that data. The low-stakes competition among peers seems to motivate students to be creative and persistent. Briefly, the steps are:

  1. The class is assigned a direct measurement video such as Cart rolls down ramp. Students are asked to explore the video and create an interesting problem that they can solve using measured data from the video. This exploration phase is typically a homework assignment.
  2. During the question creation phase, students work in groups of 3-5 to create and solve their group's challenge question. This can be a question already developed by a group member during the exploration phase, or a synthesis of ideas to create a new question.
  3. Groups are paired with another group and they swap challenge questions.
  4. During the problem solving phase, groups work to solve the challenge question presented to them, while hoping they have presented a challenge question that stumps the opposing group.
  5. During the presentation phase, groups present their solutions to the class. Class members ask questions to evaluate the solution and decide whether it is correct.
  6. The goal is to have created a sufficiently challenging question that the opposing group cannot solve it, but to be able to solve the question given to them.

This is one of the most interesting, fun, and creative learning activities we do in our class. Students rise to the occasion, given a chance to explore a situation and see how physics can be applied. During the question creation phase, they come up with questions that are more imaginative, complex, and interesting than questions I'd give them. During the problem solving phase, students are motivated by the knowledge that the problem is solvable, because their peers had to solve it in advance.

Learning Goals

Both Next Generation Science Standards (NGSS) and the new AP Physics 1 and Physics 2 courses specify that students develop their ability using science practices. The Physics Face-off gives students experience with all eight of the NGSS Science Practices:
  1. Asking questions

  2. Developing and using models

  3. Planning and carrying out investigations

  4. Analyzing and interpreting data

  5. Using mathematics and computational thinking

  6. Constructing explanations

  7. Engaging in argument from evidence

  8. Obtaining, evaluating, and communicating information

During the exploration and creation phases, students engage in the first five of these science practices in an iterative process as they work to create a challenge question they'll use to challenge their opposing group. They look at the video to determine what model applies (e.g. Are we looking at forces and acceleration? Momentum? Energy?) They explore what measured quantities are available (Can I measure the velocity? What displacement can I see? What frame of reference is best?). They see what else they can calculate using these quantities. Often they circle back and look for other quantities, or even a different model. Students are encouraged to collaborate by exchanging ideas and synthesizing the best aspects of each member's question.

When the problem-solving phase begins, student usually jump in and begin using a model and the measurements they already have to begin making calculations. When they've got a solution, students construct an explanation on their white board. They know they'll be asked to present the solution to the challenge question they received, including their measurements, assumptions they used, their models, and their calculations.

During the presentation phase, students explain their solution and defend their reasoning to their peers. Other students in the class evaluate the solution, asking questions until all are satisfied that the solution is correct, or that the errors have been identified.

Context for Use

This activity is suited for high-school and introductory college students in a physics course that uses direct measurement video. Before attempting this activity, students should have mastered basic direct-measurement video skills such as using the frame counter to measure time, and using on-screen rulers to measure position and displacement. If students have not used direct measurement video before, the Measure the Velocity of a Roller Coaster activity is a good introduction.

We use this activity near the end of a unit, when students are nearing the point of mastery of a topic.

The activity can be completed in a single class period if students and instructor stay on-task, and if students have completed the exploration phase as a homework assignment. Class time should be split into thirds for each of the phases: question creation, problem solving, and presentation.

This activity is not graded in our class. I try to motivate students by showing them the creative opportunity, and the fun of friendly competition amongst classmates.

Description and Teaching Materials

Students need computers, at least one per group, to make measurements from the video. Students also need whiteboards and dry-erase markers to exchange challenge questions, solve the problem, and present their solution. For more information about using white boards, see this blog post by Frank Noschese.

Not all direct measurement videos are equally well-suited to this activity. In our class, we've used Airplane on a string makes a conical pendulum and Cart rolls down a ramp into a spring.

Here are sample questions students suggested for the videos we've used in class:

Airplane on a string:

  1. What speed would result in a string angle of, for example, 75 degrees?
  2. If the breaking strength of the string is 50N, what angle will cause the string to break?
  3. If the string broke and the propeller stopped spinning, how far away from the center of the circle would the plane land? Assume the plane was 1.5 meters above the ground before the string broke?
  4. What is the volume of the cone made by the string?

Cart slides down ramp and into spring:

  1. What is the spring force constant?
  2. How much higher or lower would the cart end up if the spring constant doubled?
  3. What is the increase in thermal energy of the system during one complete bounce?
  4. What is the peak acceleration of the cart?

Other good candidates are for this activity are:

Teaching Notes and Tips

It will be very useful if the instructor works through solutions to possible questions in advance. In particular, the instructor should make measurements themselves. In the case of the spring cart, for example, students often have trouble deciding on and sticking with a frame of reference for vertical measurements. They'll use the top line for their initial height measurement (h = 11 cm), but then assume that h=0 when the cart momentarily stops at the low point.


This assignment is used as formative assessment. No formal feedback is given. Instead, we use student discourse during the presentation phase to assess each team's work.

References and Resources


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