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Elastic Poppers and the Art of Teaching Energy in Physics

Physics teaching thrives on the unexpected. I’ve wittered on before about how Ifeel that some of the best demonstrations — the ones that stick in students’ minds long after the lesson — are the ones that surprise, defy intuition, and demand explanation. And a lot of the time, the best tools for the job aren’t fancy bits of lab kit but cheap, unassuming toys…

Enter the humble elastic popper, stage left.

These little hemispherical plastic domes, sold in bulk as party favors, have an excellent trick up their sleeve: press them inside-out, set them down, and after a short, suspenseful pause, they launch themselves into the air. It’s simple, effective, and deeply annoying to anyone not expecting it. Perfect.

So how do we use them in physics?

1. Energy Stores and Transfers: The Setup for Surprise The popper starts in one configuration — an inverted dome sitting peacefully on the table. When you press it inside out, you do work on it, storing elastic potential energy in its deformed shape. Left alone, it sits there, full of energy but doing nothing. Then, with no obvious external force, it flips back and launches into the air, its stored energy now transformed into kinetic and gravitational potential energy.

For students, the moment of launch is oddly delightful. There’s an anticipation, a tension, a pause… and then it goes. It’s an immediate, tangible demonstration that energy is stored before being released, making it ideal for discussions on:

Elastic potential energy (Where is the energy when it’s inside out?) Work done and conservation of energy (Who put the energy in? What happens to it?) Kinetic and gravitational potential energy (How high does it go? What’s limiting its launch?) The best bit? The popper, unlike a stretched rubber band or compressed spring, hides its stored energy. To students, it doesn’t look like it’s under tension — until it suddenly is. That built-in deception makes for a great discussion starter.

1. Quantifying the Pop: How High, How Fast? A popper is a physics experiment waiting to happen. Give students a stopwatch, a ruler, and a phone camera, and they can start investigating:

Maximum height: Time the flight and use the following to estimate launch height:

Launch speed: Use this to get an estimate for the initial velocity;

Energy efficiency: Compare the calculated potential energy (mgh) to the work done (Fx) when pressing it inside-out. With a slow-motion video, students can refine these estimates and even look at whether the popper rotates in mid-air. The results often reveal interesting variations — slight differences in manufacturing, launch angle, or even the surface it’s placed on can all affect the flight.

1. Supercharging the Experiment with Phyphox For a more data-driven approach, Phyphox (the free smartphone physics sensor app) can turn this toy into a proper experiment. Here’s how:

Measuring Flight Time: Place a phone on a soft surface (like a folded jumper) next to the popper’s launch zone. Use the Acoustic Stopwatch function in Phyphox. It detects the sound of the popper launching and landing. The time between these two sounds gives the total flight time, allowing students to calculate maximum height using the formula above.

1. Tracking Acceleration During Launch:

Place a phone on a soft surface (like a folded jumper) next to the popper’s launch zone. Start the Acceleration without g sensor in Phyphox, then press the popper inside-out and let it launch from the phone. The app records the acceleration profile, showing the sudden increase in force during launch. By using N3 law and the mass of the phone the flight of the popper can be predicted.

1. Measuring Impact Forces:

Place a phone on the surface where the popper lands. Use the Acceleration (g) sensor to measure the force as the popper hits the phone. Compare impact forces for different heights, popper designs, or even different surfaces (e.g., wood vs. carpet). Using Phyphox makes the physics visible and quantifiable, taking the lesson beyond just qualitative descriptions. Students can analyze real data, compare different poppers, and even use their results to refine their initial estimates of energy conversion.

1. The Unexpected Chaos of Multiple Poppers One popper is fun. A class set of poppers is pandemonium.

Try this: get every student to press down a popper at the same time, count down, and let them go simultaneously. In an ideal world, they’d all launch at once. In reality, some pop immediately, some take a few seconds, and some… just sit there, menacingly.

What’s going on? A discussion on material properties, friction, and minuscule differences in pressure and deformation follows. Even in an apparently identical system, tiny variations create unpredictability — cue links to chaotic motion, resonance, and even quantum mechanics if you’re feeling ambitious.

1. Extensions: Thinking Like a Physicist A good physics lesson leaves students with more questions than answers. Some follow-up ideas:

Temperature Dependence: Does cooling a popper in the fridge affect its launch time or height? What about warming it up? Surface Interactions: Do different surfaces (wood, plastic, felt) affect how long it takes to pop? Mass and Material: What if you glue a small weight to the popper? How does that change its energy transfer? Resonance: Place a popper on a vibrating surface — can you trigger it without touching it? For the more mathematically inclined, students can model the popper’s behavior as a nonlinear elastic system — the kind of problem that sits at the intersection of mechanics and materials science.

Conclusion: Small Toy, Big Physics The best physics demonstrations don’t need to be complicated or expensive. Elastic poppers are cheap, easily available, and packed with physics. More importantly, they engage students — because they’re fun, unpredictable, and demand explanation.

Using Phyphox takes the activity to another level, turning an intuitive demo into a full experimental investigation. Now students aren’t just watching physics happen — they’re measuring it, analyzing it, and asking the next questions.

And let’s be honest: sometimes, the best way to capture attention in a physics lesson is to make something jump unexpectedly into the air.