July 01, 1999 Filed in: Demo Corner
Diana Hall, Bell High School, Nepean, Ontario
This is a very popular game I have played with my OAC physics class. It incorporates the concepts of conservation of energy and projectile motion.
“D-Ball” is a baseball with a D marked on it. If your name doesn’t start with the letter “D”, you will have to make appropriate changes. D-Ball is hung from the ceiling on a piece of very thin fishing line or fine thread tied to a paper clip that is hooked through the threads on the ball. A razor blade is clamped at a position just barely above the ball as it hangs straight down. A second paper clip and thread are used to tether the ball to the side just below the ceiling.
To launch the ball, burn the thread tethering the ball allowing it to swing down, pendulum style. When the string meets the blade, it is cut and the ball becomes a projectile. The students must make appropriate measurements before the launch and calculate a prediction of the landing position of D-Ball. We mark the floor and then launch D-Ball.
The horizontal distance travelled by the ball turns out to be within 2% of the theoretical prediction. Students reported that this was one of their favourite activities.
It is easy to make this demonstration into an exam question. I gave them a scale diagram and they had to calculate and mark the landing position on it.
Thanks to Brian Wegley, Genbrook HS, Glenview, Illinois for sharing this idea.
Column Editor: Ernie McFarland, Physics Department, University of Guelph, Guelph, Ontario, N1G 2W1