Introduction to Direct Measurement Video: Measure the Velocity of a Roller Coaster

Peter Bohacek, Henry Sibley High School

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This activity can be students' first exposure to using Direct Measurement Videos in physics. Students will use a video to make measurements that will allow them to calculate the speed of a roller coaster. This activity will also help students understand the concept of average velocity.

Learning Goals

Students will: learn to use direct measurement videos to make measurements apply the definition of average velocity to a real-life situation use unit conversion to compare the velocity of the roller coaster to the velocity at which cars normally drive

Context for Use

This activity is intended for use in any introductory physics course. The mathematics are very simple. However, this activity is still applicable to more advanced students because it can be used to introduce measurement uncertainty and uncertainty propagation.

Description and Teaching Materials

Students will need to download the QuickTime version of the video to their computer. Viewing the video in QuickTime allows students to control the video and advance one frame at a time. This is essential to using direct measurement videos. Students may need to be reminded that viewing the video within the web browser will not allow them to advance the video frame-by-frame. In most browsers, use ctrl-click, right-click, or two finger click and save the file to the computer.

Download the Quicktime file: Video of roller coaster 1 (Quicktime Video PRIVATE FILE 11.2MB Jul23 12) here.

The word document here shows one set of instructions that could be used with this activity. However, these are very descriptive instructions that do not allow room for student exploration. An alternative approach would be to simply give the students the video and challenge them to develop a method to find the velocity.

Student instructions for Intro to Direct Measurement Activity (Microsoft Word 2007 (.docx) 95kB Jul25 12)

Teaching Notes and Tips

There are two tricky concepts to consider when students first encounter direct measurement videos. First, students may not be aware of the relationship between the number of frames and the elapsed time. Although they may have watched many videos in their lives, they may not have considered that each video frame represents the situation at a specific time. Additionally, they may not be aware that the reciprocal of the frame rate tells the amount of time that elapses between each frame of the video. For example, the time interval shown by advancing a 30 frame-per-second video by 15 frames equals 15 frames multiplied by one second over 30 frames, or half a second.

The second tricky concept is the displacement of the train. To some students it will be immediately obvious that the train has traveled a distance equal to its own length, other students may take more time to see this relationship. Demonstrating with a meter stick and the student's hand may help. Have the student hold their hand vertically in from of them. Pass the meter stick horizontally past their hand. Ask the student to tell how far the meter stick moves in the time between the time that the front of the stick is at their hand until the time when the back end of it passes their hand.


To assess students' ability to use direct measurement video, give them another similar sample from the Direct Measurement Library. To assess their ability to use the definition of average velocity, students can be assessed with a traditional word problem that uses the concept of average velocity.

References and Resources