Wave machine

(animation from video by Rio Americano High School physics teacher Dean Baird)

Students love the visual of this colorful contraption strung across the classroom. It’s like a fun hands-on museum exhibit!

“Whoa… that shit’s tight…” – Random unidentified student to his friend while walking by my room

I leave this thing suspended in the back of my classroom for most of my waves unit since it comes in handy when trying to do a quick simple demo. It’s highly visible, allows students to keep track of individual points (“keep your eye on this green dot”), and is just a cool and fun thing for students to play with.

Making the Wave Machine

  • Instructions to construct wave machine: http://www.instructables.com/id/Candy-Wave-Machine/
  • You can also use gummy bears instead of Dots candies.
  • I have my students help make the “barbells” by recruiting students who finish their quizzes early, then I might “tip” them by letting them eat a few of the candies.
  • Don’t have ring stands/clamps? Hang the wave machine vertically from the ceiling! (Hat tip to Cypress High school physics teacher Kevin Dwyer.) This also results in an interesting phenomena of the wave velocity changing depending on its location along the tape due to the higher tension at the top and lower tension at the bottom (because… gravity).

Making Waves

  • Hit it
  • OR…
    1. Grasp like so…
      wave machine hold
    2. Torque your hand either direction…
      You can have someone make a wave simultaneously on the other side to show either constructive or destructive interference (aided by slo-mo video helps)
    3. Or torque rhythmically for a standing wave…

Questions and things to point out

  • “What’s the medium of the wave?”
  • “Is this a transverse or longitudinal wave?”
  • “What direction does the medium vibrate relative to the direction of the wave?” (“Keep your eye on that green dot. [Send a wave through.] Describe the motion of that green dot.” This is useful for helping students see the medium does not travel with the wave, and for figuring out the wave is transverse.)
  • “How might we change the wave speed?” (The speed is dependent on the medium – ways to change wave speed include adding/removing candy, changing the spacing between barbells, scooting the candies in/out.)
  • Show constructive and destructive interference (kind-of – it would help to record and replay this in slo-mo)
  • “How might you calculate the wave velocity? What equipment might you need?”
  • Do standing wave demonstrations (and calculate the velocity using velocity = wavelength * frequency)

Other Tips

  • Student: Mister! Can I eat the candy?
    Me: A buncha people put their hands all over it when we made the thing, but yeah, if you’re into that…
  • Question: Can I reuse this from year to year?
    Answer: Depends – on how ghetto you want to be. In the past, I’d try to keep it around, but during summer my classroom gets ants so they’d swarm all over it and I’d throw it away. This past year I reflected on my practices and thought… what if I just waited for the ants to go away? And they did. Unfortunately, the Dot candies got dry and most of them have cracks – but they’re still stuck to the skewers. Maybe fewer than 5% fell off over the year, so the only work I had to do was replace the small handful that cracked and fell. We’ll see how many fall over the next year. Let’s see you eat those candies now, kids.

Related Resources

Video about the wave machine: https://www.youtube.com/watch?v=FjPFW6gftas
Dean Baird’s video with instructions: https://www.youtube.com/watch?v=RCbf9_4xN_E
Alternative/supplement – PhET wave simulator – Definitely not as physically and visually impactful, but useful if you want to visualize an idealized wave made of undulating points.