Science & Technology

Why It's So Hard to Quietly Unwrap Candy in a Theater

You're two-thirds of the way through the weekend blockbuster, and the emotion is building — the love interest wordlessly gazes at the lead actor, and he gives a smoldering look in return. And then: Someone behind you is unwrapping candy. Ugh! Can't they do it quietly? Actually, no: According to research from the University of Chicago, it's physically impossible to lower the volume of an unfolding candy wrapper. The reason comes down to garden-variety physics.

Twist and Shout

In 1996, physicists Eric M. Kramer and Alexander E. Lobkovsky set out to answer this question. For a study published in the journal Physical Review E, they explained how it all comes down to energy — specifically, elastic potential energy. That's the energy that's stored as a result of the deformation of an elastic object, like the stretching of a guitar string as you pluck it. If you take the mylar material of a candy wrapper before it's been wrapped — when it's a fresh, flat sheet in the factory — it doesn't contain any potential energy. It also has one stable configuration: flat. That's where it likes to stay, and if you disturb that configuration by, say, rolling the sheet into a tube, it will unroll to settle back into its stable, flat configuration.

But if you take that mylar and crumple it up, everything changes. Every crease in the material stores elastic potential energy and complicates the material's stable configuration. Now, instead of one configuration to settle into, it has a variety to choose from. That's why you can change your mind in the middle of unwrapping a mint, and the wrapper will mostly stay where you left it.

In a presentation of his paper for the Acoustical Society of America, Kramer likened it to a ball rolling through a hilly landscape. The landscape represents the elastic potential energy as it relates to the wrapper's deformation. When you have a flat mylar sheet, the landscape is just a smooth slope into a single valley; a ball placed anywhere on that landscape will eventually roll into that valley, just like an uncreased sheet will eventually flatten out into its single stable configuration. But once you've crumpled it up, the landscape is covered with random hills and valleys; a ball placed anywhere in the landscape could settle into any random valley.

As a result, every twist and crinkle you add to the wrapper loads it with elastic potential energy, and once you unwrap it, it takes on a series of new configurations, releasing energy along the way in the form of heat, vibrations in the material, and — yes — sound.

But that doesn't explain why you can't make that sound quieter. For that, you need an experiment.

The Sound of One Candy Wrapping

For their study, Kramer and Lobkovsky took a bunch of mylar sheets of various thicknesses and crumpled them each by hand 30 to 40 times. Then they set up recording equipment, flattened out each sheet the best they could, and twisted and flexed it over and over. They wanted to find out whether the thickness of the sheet had any impact on the sound it made.

When they analyzed the recordings, they found that the sounds were basically a collection of clicks — each one a release of potential energy. Thicker sheets produced fewer but louder clicks, while thinner sheets produced more clicks, but they were somewhat quieter. But overall, the energy of these sound waves varied drastically — the smallest to the largest clicks ranged in energy by at least a factor of one million.

That shows that it's impossible to quiet your candy wrapper: If you unwrap slowly, you'll slow down the frequency of your clicks, but you won't turn down their volume, just as you can slow down the rate at which you roll a ball up a hill but you can't control it once it rolls down the other side. The best thing to do when you want a snack in the theater? Just open it as fast as you can — time is one element you can control.

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For more answers to everyday science questions, check out "Ask a Science Teacher: 250 Answers to Questions You've Always Had About How Everyday Stuff Really Works" by Larry Scheckel. The audiobook is free with an Audible trial. We handpick reading recommendations we think you may like. If you choose to make a purchase, Curiosity will get a share of the sale.

Written by Ashley Hamer August 16, 2019

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