Sensing A De-Motion

(I and a couple of coworkers are working the registers. We’re all roughly college age. Coworker #1 is playing with the motion sensor on the conveyor and notices that part of the plastic holding it on is broken.)

Coworker #2: “Don’t touch it; you’ll break it. What is it, anyway?”

Coworker #1: “It’s the motion sensor.”

Coworker #2: “For what?”

Coworker #1: “To make the belt move.”

Coworker #2: “Wait. No way. It moves with a motion sensor?”

(Starts playing with it, putting her hand in front of and away from the sensor, making the belt move.)

Coworker #1: *laughing* “Yeeaaaah. Congratulations, you’ve figured out what most kids figure out in five seconds. How did you think it moved?”

Coworker #2: “By weight! Like, it stops when there’s something on it. That’s why I always hit it to make it start moving again.” *she demonstrates* “See? It works at least.”

Me: *laughing also* “Because your hand goes in front of the sensor! Have you really not known this?”

Coworker #1: “And HOW long have you worked here?”

Coworker #2: “…A year.”