Video · Teachers Media
Shattering a glass video
The famous "singer shatters a wine glass" demonstration — an example of resonance, where a sound of exactly the right frequency drives an object at its natural frequency until it fails. It's dramatic, and it's a genuine window into a physical principle that turns up everywhere from bridges to musical instruments.
About this video
Every object has natural frequencies at which it prefers to vibrate — flick the rim of a wine glass and you hear its natural frequency ring out. If you deliver energy to that object at exactly that frequency, each pulse arrives just in time to add to the previous oscillation, and the amplitude grows. For a wine glass, given enough amplitude, the flexing exceeds what the glass can withstand and it fails.
The interesting teaching moves are around the conditions the demonstration reveals. First, the frequency has to be right — off by even a small amount and no energy transfers efficiently. Second, the sound has to be sustained — a single loud shout doesn't deliver enough total energy. Third, the object has to have low enough damping that the oscillation can build up rather than die away with each swing.
Resonance is also worth teaching because it turns up in genuinely important places pupils will meet later: bridges collapsing (Tacoma Narrows), buildings in earthquakes, MRI machines, tuning circuits in radios, musical instruments. Once pupils have the idea from a wine glass, they can see it everywhere.
Why the demonstration is hard to run in a classroom
You almost certainly can't safely shatter a wine glass live in a classroom — it needs a specific type of glass (crystal, thin-walled), very precise frequency matching, sustained high volume, and eye protection. What you can do:
- Play the wine-glass frequency and pupils sing the note. They'll hear the glass sing back sympathetically.
- Show a slow-motion video of the demonstration (many exist online). Freeze the moment where the flexing exceeds the glass's tolerance.
- Model resonance with mass-on-spring simulations or a driven pendulum — the physics is identical.
Discussion prompts
- What everyday examples of resonance do your pupils already know, without knowing the word?
- How do you handle demonstrations that are famous but hard to run safely — replace with video, alternative demo, or drop?
- Where else in the curriculum could pupils meet resonance (earthquakes, MRI, musical instruments)?
Try this in your classroom
- Play the natural frequency of a wine glass through a speaker, then ask pupils why the glass "rings" when the tone plays.
- Show the Tacoma Narrows Bridge collapse video. Ask pupils to explain what they're seeing in terms of resonance.
- Set up a driven-pendulum demonstration (a pendulum with a periodic push). Vary the driving frequency and watch what happens to amplitude.