That Went Down The Tubes

(I’m a teacher’s assistant. A physics teacher has a demonstration that he’s used for years: he draws a cello bow across a glass tube, making it hum, and shows how gradually dipping it in water changes the pitch. This year, the demonstration takes a different turn.)

Teacher: “As you can see, I have a glass tube, a cello bow, and a bucket. Now, we’ve been talking about frequencies and vibrations, and I’m sure you remember the slow-motion video of the violin from last week. I’m going to slowly draw this bow across the tube. What do you think’s going to happen?”

Student #1: “It’s probably going to make a noise.”

Student #2: “No, no, it’s not flexible like the strings. Nothing’s going to happen.”

Student #3: “But remember, we watched the video with wine glasses? Glass can-–”

Student #4: *interrupting* “IT’S GOING TO EXPLODE!”

Teacher: “Well, let’s see.”

(He places the tube in its stand and begins to pull the bow. The tube instantly shatters, and the fragments fall into the bucket that he would have otherwise filled with water.)

Teacher: “[Student #4], very good. The minute vibrations induced by the bow are too much for a fragile glass tube like this to handle. Next week, we’ll introduce tubes of varying thickness to see what happens then.”

(After class, I hear the story.)

Me: “So, I hear your tube demonstration went wrong today.”

Teacher: “Ah, no, it went perfectly. The important thing isn’t the expected outcome; it’s that they got a chance to learn something new.”

(He thinks for a second.)

Teacher: “And that they don’t realize I screwed up a demonstration I’ve done for every class for the past fourteen years.”