Hi I’m Craig! My vocal chords are made up of two vibrating mucus membranes, and this is mental floss on YouTube. Today I'm going to answer Bridget Kline’s Big Question: Why does your voice get higher when you inhale helium? Let’s get started!

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First lets do a refresher on sound. I'm sure you remember this from your many science classes, so this is gonna be the crash course version. Put simple, we’re able to hear sound thanks to vibrations that travel through air. Those vibrations form sound waves. Here’s an example of sound: MAAHH!

The speed of sound is how fast sound waves travel. The speed depends on the medium that the sound waves are going through. Sound frequency is how often that medium’s particles vibrate as the wave travels through it. Frequency affects the pitch of a sound. This is all coming back to you, right? Great.

When we speak we must produce vibrations. This happens without vocal chords which are two vibrating mucus membranes stretched across the larynx. Air travels from your lungs to your larynx which makes your mucus membranes vibrate. It’s the frequency of this vibration that affects the pitch and volume of your voice.

Then the sound travels through your vocal tract which is made up of your pharynx, mouth and nasal cavities. Here air vibrates affecting your voice’s timbre. Timbre is basically the sound’s character and quality. It’s also a way to indicate that you are chopping a tree down.

Now let’s talk about helium. Helium’s speed of sound is three times faster than the speed of sound in air. This is because helium atoms have a lower mass than the mass of oxygen and nitrogen atoms. Think about how balloons of helium rise. That’s because is less dense than air. It's atoms move quicker, which means it can carry sound quicker.

Let’s imagine you just inhaled helium. When you talk through those vibrating vocal chords I mentioned earlier, the frequency is gonna be the same, so the pitch of your voice is also gonna be the same. Your voice is altered thanks to the vocal tract where helium is causing the sound waves to be faster. Basically, inhaling helium affects the timbre of your voice, not the pitch, like many people believe.

Now it’s time for my lecture: inhaling helium can cause death by asphyxiation, which has happened before. I do not recommend trying this at home, or at any public establishment!

That said, you can reverse this phenomenon by inhaling denser gasses that you might have laying around, like xenon or sulfur hexafluoride. Who doesn’t have that?! I have sulfur hexafluoride parties all the time. But you really shouldn’t do that!

Thanks for watching mental_floss on YouTube, made with the help of these lovely mucus membranes. If you have a big question you would like answered, leave it in the comments below. See you next week!

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