# Direct Measurement Video of a Toy Car Accelerating

## Summary

This is a short activity intended to allow students to practice kinematics using a video of a familiar object: a spring-powered toy car. Students measure displacement and elapsed time from the video and use these measurements to calculate average speed. Observing that the car has an initial speed of zero, students can find the final speed and acceleration.

Students will use a QuickTime video recorded at 240 frames per second, making measurements directly from the video using a ruler 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:

• measure displacement and elapsed time from a video
• calculate average velocity using these measurements
• use the definition of average speed to find the final velocity of the car
• calculate the average acceleration of the car
• express the motion of the car graphically using a velocity vs time graph

## 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 concepts of displacement and elapsed time, average velocity and average acceleration. This activity is intended to be an opportunity for students to apply these 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.

## Description and Teaching Materials

Here is an example of questions that can guide students through this activity: Student instructions for Direct Measurement of Toy Car Accelerating (Microsoft Word 2007 (.docx) 27kB Feb20 13)

These instructions are highly scaffolded, giving students step-by-step instructions. An instructor may chose to provide less detailed instructions to encourage independent thinking and problem solving.

Here is the QuickTime video file: Direct Measurment Video: Toy Car Accelerating (Quicktime Video 5MB Mar24 13)

## Teaching Notes and Tips

Students can work individually, or in small groups with one computer per group. Alternatively, the video can be projected and the class can collect data (numbers of frames and distances) together, and do calculations 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 does not allow students to advance frame-by-frame.

## Assessment

Students can be assessed using a standard word-problem that provides an elapsed time and a distance for an accelerating object that begins from rest. Alternatively, students could be asked to apply this technique to a new situation. For example, students could measure the drop time for an object in free fall (ideally using video) and use the approach they learned here to measure the acceleration of an object in free fall.

## References and Resources

The Physics Classroom website has tutorials that can help with the topics covered here: 1-dimensional kinematics

PhET has a simulation that allow students to explore this accelerated motion: The Moving Man