Air Hockey Build: Force Pairs Between Mallet and Puck

Building an Air Hockey Table

1The Cedar Hollow Community Makerspace is a workshop in an old fire station where neighbors share 3D printers, a laser cutter and hand tools. This winter its teen club decided to build a full-size air hockey table for the lobby. A fan blows air up through hundreds of tiny holes in the tabletop, so a flat plastic puck floats on a thin cushion of air and glides with very little friction. Low wooden rails run around the edges, and a goal slot sits at each end. Players strike the puck with a heavier plastic striker called a mallet, trying to send it into the other player's goal.

2Club members Linnea Abara and Tobias Kaminski wanted to know what happens to the forces when a mallet hits a puck. A volunteer engineer, Mr. Bertrand Oyelaran, lent them two thin force-sensing pads. They stuck one pad on the face of a 160 g mallet and the other on the edge of each puck they printed. Each pad records the largest force it feels during a hit.

3To keep their hands out of the data, the pair did not hold the mallet. A rubber-band launcher sent the mallet gliding across the table at 2.0 m/s into a puck resting in the center. A phone filmed every hit in slow motion from above, and a meter stick taped along the rail let them find each object's speed just after the hit. Each hit lasted only about 2 thousandths of a second. They printed pucks with masses from 10 g to 80 g and kept the mallet, the launcher setting and the table the same. Each result in Table 1 is the average of three hits.

4During practice games the club had already noticed two problems. Very light pucks sometimes lifted off the air cushion after a hard hit and flew over the rail. Also, the mallet's force pad is rated for pushes of about 70 N, and the club does not want to damage it. At the same time, players complained that slow, heavy pucks made the game dull. Linnea and Tobias hoped their data would show which puck the club should print for the finished table.