D-Ball
July 01, 1999 Filed in:
Demo CornerDiana Hall, Bell High School, Nepean, Ontario
Diana_Hall@ocdsb.edu.on.ca
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.
![D-ball](d-ball.png)
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 Tags: Energy, Projectile Motion