# Day 100: Acceleration Challenge 2014 (featuring Ubersense and Desmos)

*College-Prep Physics:* This actually happened a few days ago, but it’s too awesome not to share.

In an attempt to differentiate acceleration practice, I gave students a few choices. They could work on practice problems, work on graph interpretations, or do an acceleration challenge. Only one group of students from all 3 of my sections decided to go with the challenge. The goal of the challenge is to determine how far up the ramp to release a free-rolling cart so that it collides with a constant speed buggy at the bottom of the ramp. Students were not allowed to attempt any collisions, but could take data in order to determine the speed of the buggy and the acceleration of the cart down the ramp.

There are several ways to determine the cart’s acceleration:

- Collect position-time data by hand and calculate acceleration using kinematics.
- Film it and use Logger Pro or Tracker video analysis
- Use a motion detector and get the slope of the velocity-time graph

This time, the group decided to try the Ubersense app to take video and use the frame-by-frame feature to extract position-time data rather than using a stopwatch. They marked off 1 meter distances and videoed the cart rolling down the ramp. No need for the whole trip to be visible within the entire video frame — we can follow along with the cart and use the frame-by-frame playback to extract position-time data from the video:

Then they input the data into Desmos and tried to find a parabola of best fit to model the cart’s position as a function of time.

Next, they found the speed of the constant velocity buggy. Then I told them how far away from the crash point (X) the buggy would start. They then calculated the time it would take the buggy to travel to the X. Then they used that time and the Desmos graph to determine the distance the cart would travel down the ramp in the same time (e.g., the starting position of the cart).

As you can see at the beginning of the post, they nailed it!

#CAPM

Here’s my version of a similar challenge I give my students called “Don’t Get Steam Rolled” http://www.youtube.com/watch?v=71PzTIy9XLc

That is impressive! So cool.