Direct Measurement Videos: Extracting Data from Video Clips
By Peter Bohacek, Henry Sibley High School
Presented here is an alternative that has become possible now that we can use digital media to deliver and assess teaching. Instead of a verbal description or drawing, along with explicitly stated numerical information, students can be given a video clip that contains data to solve a question. For example, this video clip shows a video of a tennis ball bouncing across a stage. Students are asked to view the video clip, extract data they need from the clip and determine the angle at which the ball lands on the ground during the second bounce.
On first view, it may seem surprising that students can use the information in the video shown here to determine the angle at which the ball hits the ground. The only numerical information given is the horizontal distance between two vertical poles. In order for students to solve this problem they have to go one step deeper in their thinking than they would in a problem where the numerical information is given explicitly. First, they must determine which data they need and how to use the video to get it. Only once they have extracted the data they need can they begin the process they'd use to solve a traditional word problem.
For this particular example, students need to recognize that the velocity of the ball has two components, vertical and horizontal, and that they can determine these by two different means. In both cases, they need to measure a time interval, which they can do by counting the frames in the video and dividing by the frame rate. For the horizontal velocity, students can count the number of frames it takes for the ball to pass between the two vertical posts. Since they know the distance between the posts, they can use the time to determine the horizontal velocity. Similarly, students can count the frames to find the time during which the ball is airborne between bounces and use the equations of motion for an object moving in free fall to determine the vertical velocity of the ball when it lands. Finally, students use vector addition to combine the two components of the velocity to find the angle at which the ball is moving when it lands.
This approach can be adapted to a wide range of mechanics topics. Using time and distance data extracted from video clips, students can determine acceleration, force, impulse, and mechanical energy. Here is a clip showing a car braking on an ice rink (Quicktime Video 1.4MB Feb27 11). Students can use time and distance to determine acceleration. Using Newtonian mechanics, they can determine the effective coefficient of friction between the ice and the tires.
Methods for Integrating Video Clips in Class
There are several ways in which these exercises can be delivered to students. A teacher can simply post the video on a web site and propose a question. A teacher can provide guidance, by prompting students to determine values they'll need to find the final answer. For example, in the video of the ball shown above, they teacher could ask students to find the time for the ball to travel between the posts, time the ball is airborne, and so on. This scaffolding approach can help students as they learn to solve these types of problems. As students develop their ability, the teacher can provide less scaffolding.
These problems can also be delivered using an online homework system, such as WebAssign, Quia, or Moodle. In this case, the students can get instant feedback as they work.
Video Files for Use in Class
For each video below there is a Flash version for easy viewing and a QuickTime version that can be downloaded. For use in class, it is recommended to use the QuickTime version so that the video can be advanced frame by frame, allowing for a measurement of time intervals.
Example Activities Using Video Clips
These are activities that use this technique. Each of these pages includes detailed information showing how to use video clips to teach specific physics concepts.
Jump down to Video Files | Classroom Activities that use Video Clips
Using Video Clips for Data Analysis
Historically, teachers use word problems or context rich problems to develop and assess students' ability to use science and math techniques. For example, students are given a problem that tells them the velocity at which a car drives down a road, and the length of time it drives, and are asked to find the distance the car will move. These problems are effective ways of teaching and learning, as evidenced by the fact that generations of scientists honed their skills using word problems in their textbooks.Presented here is an alternative that has become possible now that we can use digital media to deliver and assess teaching. Instead of a verbal description or drawing, along with explicitly stated numerical information, students can be given a video clip that contains data to solve a question. For example, this video clip shows a video of a tennis ball bouncing across a stage. Students are asked to view the video clip, extract data they need from the clip and determine the angle at which the ball lands on the ground during the second bounce.
On first view, it may seem surprising that students can use the information in the video shown here to determine the angle at which the ball hits the ground. The only numerical information given is the horizontal distance between two vertical poles. In order for students to solve this problem they have to go one step deeper in their thinking than they would in a problem where the numerical information is given explicitly. First, they must determine which data they need and how to use the video to get it. Only once they have extracted the data they need can they begin the process they'd use to solve a traditional word problem.
For this particular example, students need to recognize that the velocity of the ball has two components, vertical and horizontal, and that they can determine these by two different means. In both cases, they need to measure a time interval, which they can do by counting the frames in the video and dividing by the frame rate. For the horizontal velocity, students can count the number of frames it takes for the ball to pass between the two vertical posts. Since they know the distance between the posts, they can use the time to determine the horizontal velocity. Similarly, students can count the frames to find the time during which the ball is airborne between bounces and use the equations of motion for an object moving in free fall to determine the vertical velocity of the ball when it lands. Finally, students use vector addition to combine the two components of the velocity to find the angle at which the ball is moving when it lands.
This approach can be adapted to a wide range of mechanics topics. Using time and distance data extracted from video clips, students can determine acceleration, force, impulse, and mechanical energy. Here is a clip showing a car braking on an ice rink (Quicktime Video 1.4MB Feb27 11). Students can use time and distance to determine acceleration. Using Newtonian mechanics, they can determine the effective coefficient of friction between the ice and the tires.
Methods for Integrating Video Clips in Class
There are several ways in which these exercises can be delivered to students. A teacher can simply post the video on a web site and propose a question. A teacher can provide guidance, by prompting students to determine values they'll need to find the final answer. For example, in the video of the ball shown above, they teacher could ask students to find the time for the ball to travel between the posts, time the ball is airborne, and so on. This scaffolding approach can help students as they learn to solve these types of problems. As students develop their ability, the teacher can provide less scaffolding.These problems can also be delivered using an online homework system, such as WebAssign, Quia, or Moodle. In this case, the students can get instant feedback as they work.
Video Files for Use in Class
For each video below there is a Flash version for easy viewing and a QuickTime version that can be downloaded. For use in class, it is recommended to use the QuickTime version so that the video can be advanced frame by frame, allowing for a measurement of time intervals.loading the player
A person sliding across ice. (Quicktime Video 789kB Feb27 11)This video can be used to determine the coefficient of friction between the person's shoes and the ice.loading the player
CO2 powered rocket cart (Quicktime Video 3.4MB Mar1 11) This video can be used to determine the acceleration of the rocket cart. loading the player
A mass hanging on a spring (Quicktime Video 175kB Mar2 11) This clip can be used to find the spring constant of the spring. loading the player
Falling wheel (Quicktime Video 1020kB Mar2 11) This video can be used to find the acceleration of the wheel and the rotational inertia of the wheel. loading the player
Wheel accelerated by a falling weight (Quicktime Video 501kB Mar2 11) This video can be used to find the acceleration of the wheel and the rotational inertia of the wheel.
