# Direct Measurement of a Hockey Slap Shot

#### Summary

This is an example of an open-ended problem in that students are given little numerical information and several different strategies and concepts can be used. Students should be familiar with the concept of velocity, acceleration, Newton's laws of motion, and the concepts of momentum and impulse. Unlike traditional a word-problem where students are given the numerical information they need to solve the problem, students must make measurements from the video to determine their answer. Ideally, students are not given hints or even told which concepts to use, as these steps are essential parts of their analysis.

Students will use a high speed video recorded at 240 frames per second, making measurements directly from the video using a frame-counter, a ruler and numerical data 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

- apply the concepts such as velocity, acceleration, force, impulse, momentum using a realistic video of a hockey slap shot

- make accurate measurements from a direct-measurement video

- to determine a method to find the average force exerted by the stick on the puck while they are in contact

- analyze the results of their work for validity

## Context for Use

- use frame-counting and unit conversion to make time measurements from the video
- use the ruler to make position measurements
- use these measurements to calculate quantities such as velocity or acceleration

If students have not had experience, with using direct measurement video, instructors may want to assign Introduction to Direct-Measurement: Measuring the Velocity of a Roller Coaster. In addition, it is helpful if students have had some previous experience with open-ended problem solving.

Compared to other similar activities in this library, this activity has a medium level of difficulty.This can be a written homework assignment, an in-class activity, or a group assignment. Students will need access to a computer to view and analyze the video.

This style of problem can seem challenging to students at first. Students may need coaching to keep them from becoming discouraged. Encourage them to persist. Remind them that the solution is within their grasp. One student's reaction to this activity was: "This problem seemed impossible until someone showed me how to do it. Now it seems obvious." Another students commented that she like this activity because when she found the solution, she felt "smart". Having the problem explained to them will satisfy their curiosity, but prevent them from achieving the satisfaction of figuring it out for themselves.

## Description and Teaching Materials

The simplest and most challenging prompt is to simply ask students to use the video to determine the average force exerted on the puck by the stick while they are in contact. Many students are not accustomed to this type of open-ended problem solving, so the instructor needs to facilitate and coach to encourage students to persist, and to carefully guide students without revealing the solution. In particular, encourage students to consider relationships they know, such as the relationship between force and acceleration, or the relationship between momentum and force. Although they may initially find this process frustratingly different from traditional problem solving, many students report a feeling of satisfaction upon solving this type of question.

Here are two prompts that the instructor can give students if needed:

- Ask them to determine the velocity of the puck after it is no longer in contact with the stick. This may lead them to consider using this value to calculate the acceleration or change in velocity of the puck.
- Ask students to determine the length of the time interval that the stick and puck are in contact.

The student instructions below include these and other prompts and make this question much easier, because they guide students to the solution. Instructors are encouraged to modify these instructions to suit their students' experience with this type of analysis. Giving fewer prompts may make finding the solution more rewarding and satisfying.

The Hockey slap shot video page contains all the available file types for this video.

Student Instructions:

Hockey Slap Shot Instructions (Google doc)

Student instructions for sliding and rolling ball (Microsoft Word 2007 (.docx) 662kB Mar24 13)

## Teaching Notes and Tips

The time required to solve this problem varies greatly. Some students will see a path to the solution quickly and complete the activity in as little as 10 minutes. Some students can become frustrated or impatient if they don't see a path to the solution. The instructor's job is to provide encouragement, and as few hints as possible to keep students on task.

If this activity is used in class, the instructor might want to have another activity available for students to work on if they complete this one. That way the class environment stays focused so all students can work to complete this problem.## Assessment

There are two main goals, and each can be assessed differently. To assess student ability in using videos for open-ended problem solving, use another of the activities in this resource. For example, consider:

Direct Measurement Video: Rotational Inertia of a Bike Wheel

or

Direct Measurement Video: Friction of a block sliding on a Ramp