Jeffrey Wetherhold from Parkland High School, Allentown, PA makes extensive use of video in his physics class. When experiments are difficult to create for the classroom, he has his students collect and analyze data using the video analysis feature of Logger Pro.

He recently sent us an activity that he uses with his students. He shows a video that is counter intuitive; the video shows a ballistics cart moving along a horizontal track. Halfway down the track, a ball is ejected from the cart. The cart and ball continue moving forward; however, shortly after that, they both start to move backward.

After showing the video to his students, he has them investigate the motion using video analysis in Logger Pro. The photo below shows the trace of the motion of the ball. The larger bright dot is actually from the last frame of the movie.

How can you explain the cause of this motion?

Download Wetherhold’s video and Logger Pro file »