Sonoluminescence Is Light Made From Sound
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How hard can you punch? Chances are it's nothing compared to the mantis shrimp: its tiny claws strike so fast that the shock wave can actually produce light. This phenomenon is called sonoluminescence, and here's how it works: if an ultrasonic sound wave—that is, one with a frequency far above that of human hearing—hits water, it pushes the water faster than it can react, forcing its pressure to drop suddenly. That leaves behind an area of low pressure in the form of tiny gas bubbles. The process of creating that gas bubble is called cavitation. At this point, it gets really strange: because these cavitation bubbles have much lower pressure than a regular bubble, they immediately collapse, rapidly increasing the pressure inside the bubble. That collapse makes the bubble hotter than the surface of the sun and produces a tiny flash of light. That's sonoluminescence. It's not just the mantis shrimp that makes this happen; things like firing a gun underwater and applying an ultrasonic field can also bring about this effect. Scientists don't yet fully understand why it occurs, but they have a few theories. Explore them in the video below.
The Doppler Effect Tells You A Siren Is Passing And The Universe Is Expanding
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You're probably familiar with the sound of a siren (or a car horn, or a rumbling semi truck) as it approaches and then passes you. The sound starts low and quiet, then begins to rise in pitch as it gets closer, then gradually drops in pitch as it passes and moves down the road. This change in pitch is known as the Doppler effect, and it may surprise you to learn that it's the same phenomenon that tells astronomers our universe is expanding.
Keep Your Music Volume Down To A Microwave's Beep
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According to the World Health Organization (WHO), nearly half of people ages 12–35 in middle- and high-income countries are exposed to unsafe levels of sound from their phones, MP3 players, and other personal audio devices. As a result, hearing damage in teens and young adults is on the rise. Noise-induced hearing damage is irreversible, and can lead to real quality of life issues including trouble understanding your loved ones and a constant, high-pitched ringing known as tinnitus. So how do you listen to your favorite tunes without needing a hearing aid in a few decades? An "unsafe listening level" depends on how long you're listening. The WHO defines 85 decibels as the highest safe exposure level when you're listening for eight hours or less. That's plenty loud; roughly the volume of a microwave beep, an alarm clock, or a blender. But if you were to crank up an Apple iPod to its maximum volume—102 decibels—you could listen for a maximum of five minutes before you risk hearing loss. This example may sound extreme, but add in the background noise of a crowded train car or the hum of an airplane and you may need to crank the volume that high to even make out the words in a song. That's why hearing experts also recommend noise-isolating or, better yet, noise-canceling headphones in loud environments, since they make it easier to listen at a lower volume. Explore the issues of hearing loss with the videos below.
You Do Hear The Ocean In A Seashell—But Only By The Ocean
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Have you ever held a seashell to your ear and listened? You've probably been told that you were hearing the ocean, or, from more scientifically minded folks, that it was just the sound of the blood pulsing through your ears. In fact, the truth is closer to the first explanation than the second. If you were to listen to a seashell, then run around for a few minutes before listening again, your heart would beat faster but there would be no difference in the sound you heard in the seashell. That means the sound you hear isn't just your blood.Here's what's really going on: a shell is what's known as a resonant cavity, like that of a glass bottle or the body of an acoustic guitar. The same way that a plucked string makes the body of the guitar vibrate, the sound waves around the shell make it vibrate ever so slightly. Therefore, if you're near the ocean, you'll hear the actual vibration of ocean sounds, but if you're in the park, you'll hear the ghostly vibrations of the birds and the breeze. The same vibration affects regularly shaped cavities like water glasses, too, but nobody hears the ocean in a water glass—just in a seashell. That's because a water glass generally has one frequency that makes it vibrate the most, whereas the seashell's irregular shape makes it vibrate at many different frequencies. That's why you hear a "whoosh" like an ocean wave instead of a single soft tone. Learn more about the science of sound with the videos below.
Why Music Is Getting Louder
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It's not just you: over the last several decades, music has been getting louder. Like rival architects building ever taller skyscrapers, record companies have been competing to make their music louder than that of their competitors. The hope is that if a song on the radio is louder than the one that came before, listeners will notice and decide to buy that record over another. This sonic arms race has been dubbed the Loudness War.Unfortunately, this war has consequences for recorded music that go far beyond volume. Audio engineers can't just turn up the loudness on an individual track, since all music has a volume ceiling, or "peak," beyond which audio will sound distorted. Engineers can get around this with a process known as dynamic compression, which makes the quiet parts louder and the loud parts slightly quieter. The result is an overall impression of loudness with much less nuance and variation. What's more, research has found that louder music doesn't necessarily lead to more record sales. Learn more about the Loudness War with the videos below.