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It's an old cliche: an opera singer hits a note so high, it breaks a wine glass. It may seem over the top, but with a little science (and an amp), you too can break a glass like the finest soprano!
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Michael Aranda: Remember that scene in Prisoner of Azkaban where the lady in the Gryffindor painting tries to break her wine glass with her voice?

Even though she doesn't succeed, you might be able to, thanks to science.

Sound is just vibrations and it can break glass by making it vibrate so hard that it shatters. 

See, every material has what's called a resonance frequency. The frequency at which it will naturally tend to vibrate. That frequency, or frequencies since there can be more than one, just depend on its physical properties. 

A guitar string, for example, will vibrate at its resonance frequencies when you pluck it, which is what produces the sound. 

Since it's easy for something to vibrate at its resonance frequency, when it's hit with sound waves of that frequency, its molecules will start oscillating back and forth with the wave. 

Those vibrations will get stronger and stronger, like how a swing will go higher and higher if you push it at exactly the right intervals. And if something vibrates hard enough, eventually the vibrations will stretch it to the point that it breaks.

Most things can vibrate pretty hard before breaking, but even strong materials, like stone and concrete, have their limits.

A glass is much easier to shatter, especially if it's thin. It also helps if it's old or cheap because older and cheaper glasses are more likely to have flaws that can act as seeds for cracks to form

We here at SciShow don't recommend you destroy your glassware or put yourself in situations where you can get ht with flying shards of glass but, hypothetically, to break a glass with sound, you'd first need to figure out its resonance frequency by tapping ti gently with a fork or rubbing a wet finger around the rim of the glass until you hear it sing. 

That's the note to match. It's most likely just over 500 hertz, or vibrations per second, like a high C. 

Some glasses might be harder to crack if the glass is too thick or the right note is out of your vocal range. 

And you have to be loud. Over 100 decibels. That's louder than your hair dryer or vacuum cleaner.

When the MythBusters had rock singer Jamie Vendera try this, he attempted to break 12 different glasses before finally shattering one by singing a 556 hertz note at 105 deciblles. 

The problem is, to break the glass with just the power of your lungs, you'd have to hold the glass in front of your face, which means that if you succeed, the glass would shatter right in front of you.

That is a very bad idea and please don't try it.

Instead you can put a safe distance between you and the glass, grab a mic and amp, and crank up the volume. But don't go overboard= you can shatter the glass with any frequency if the volume is loud enough.

Sound is just pressure waves of air, and if you increase that pressure enough, you'll smash the glass by force. 

That's not nearly as cool and besides, you'd probably rupture your eardrums too, which is another thing we don't recommend.

A little boost on the right note will break the glass easily, without destroying your ears. 

Once you're all set up, put a straw in the glass and start singing into the mic. Adjust your pitch until you see the straw start to bounce around and that's how you'll know you're close. 

If you can hold the right note for several seconds, the glass will break. 

Good luck and be careful cleaning up afterward.

Thanks for asking, and thanks especially to all of our patrons on Patreon who keep these answers comming. 

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