This part is an accessory for the PASCO Rotating Platform used for a Conservation of Angular Momentum experiment.

https://www.pasco.com/products/lab-apparatus/mechanics/centripetal-force-and-rotation/me-8951

Mount the Ball Catcher to one arm of the rotating platform.
With a projectile launcher, fire a projectile into the catcher, causing the platform to rotate as the linear momentum is converted into angular momentum.