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# How to Teach with Direct Measurement Videos

Use Direct Measurement Videos to make measurements and solve physics problems.

For an introduction to the techniques used when analyzing Direct Measurement Video questions, see the example activity Introduction to Using Direct Measurement Video: Determine the speed of a Roller Coaster

Direct Measurement Videos are intended to be used when teaching introductory physics mechanics at the high school or college level. There are several ways these videos can be used.

Screen shot from a video of a metal cylinder sliding across a table (Quicktime Video 107kB Jul7 12)

### 1. As a replacement for word problems

Instructors can present a video to students and ask them to solve a particular problem. For example, an instructor can give students the video shown at right, which shows a metal cylinder sliding to rest on a lab table and ask them to determine the increase in thermal energy of the table an metal cylinder. For this video, students measure the distance from the zero cm mark to the stopping point, the time interval. They use the fact that the object comes to rest (vf = 0). Assuming that the acceleration is constant, they can use these values to find the acceleration and initial velocity. Finally, they'd calculate the kinetic energy of the cylinder at the zero cm mark. Since they cylinder stops, all the kinetic energy is converted to thermal energy. This type of lesson can be structured as a group activity during class, or as homework. The instructor can provide scaffolding, for example, by having a discussion about the physics concepts they'll need to solve the problem, or to remind them about how to use the frame-counter to measure time intervals. An example of a lesson of this type is Using Direct Measurement Video to find the acceleration of a rocket-powered cart

Screen shot from a Video of blowdart colliding with a cart (Quicktime Video 1.3MB Jul7 12)

### 2. As a way to verify a physics concept

Instructors can present a video and ask students to show how the data in the video can be used to demonstrate a physics concept. For example, the video at right shows a blow-dart colliding with a foam block attached to a low-friction cart. Students can measure the linear momentum of the blow-dart before the collision, and compare it with the momentum of the dart and cart after the collision. Students can be asked to determine whether and why linear momentum is conserved in this situation. An example of an activity using this approach is Direct Measurement Video Analysis - Blow-Dart Collides With Cart

Students can also practice making measurements that include uncertainty. In this case, they can also use rules for uncertainty propagation when doing calculations. This is especially useful when comparing quantities to check for conservation. In the example of the blow-dart and cart, momentum is conserved, within the margin of certainty.

Screen shot from a video of a cart rolling down a ramp into spring (Quicktime Video 2.7MB Jun24 14)

### 3. As an open-ended, or "goal-less" problem

Instructors can present a video clip and ask the students to suggest a problem, or quantity they can determine, and develop a solution. For example, this clip at right shows a low friction cart rolling down a ramp and colliding with a spring at the bottom of the ramp. The video is filmed with two separate cameras, so you can see how far the spring is compressed when the cart reaches the low-point of its motion. There are many possible quantities students could determine using measurements from this video, including the force constant of the spring, the loss of energy when the cart re-bounds to the top of the ramp, or the number of bounces before the cart comes to rest.