Collision Forecasts at the Park Table-Tennis Corner

Practice Before the Park Games

At a city park's table-tennis corner, a science club sets up a practice lane on a smooth table. Instead of playing a match, the club studies collisions. A collision happens when objects moving toward one another, or a moving object and a resting object, hit. Moving objects have energy. The club looks for changes in motion, shape, and sound during each collision.

First, the students put a small, lightweight foam target at a marked spot. They roll a table-tennis ball toward it from the same starting line. An adult checks video recordings to group the ball's speed just before contact as slow, medium, or fast. The students change that incoming speed. They keep the ball, target, starting line, and table surface the same.

After each hit, they measure how far the target slides from its marked spot before stopping. They reset the target before the next roll. They repeat each speed three times. In these class trials, the target travels the same distance on the three rolls at each speed. The graph shows that distance. After contact, the ball rolls more slowly and the target begins moving.

Next, an adult sets up two different things for the ball to hit: a loosely hanging cloth and a paddle held upright. The students use the same ball and the same medium incoming speed. They repeat each test three times. Each time the ball hits the cloth, the cloth bends and swings, a faint rustle is heard, and the ball stops. Each time the ball hits the paddle, a click is heard. The ball travels back toward its starting line, more slowly than it approached. The adult keeps hands clear of the ball's path.