If you have a five-cups-a-day habit like we do here at Shmoop, you've likely poured milk into tea or coffee before—and then watched, transfixed, in a pre-caffeine trance. The milk swirls around until it mixes with the coffee or tea, producing a mixture of milk and caffeine. Mmm, caffeine.

What's that? What's our point? Sorry, we forgot. We haven't had our coffee yet today.

Oh, right. The milk swirling in coffee is an analogy for the way sound travels through and interacts with the stuff around it. Sound, like any mixture, can't be made on its own. You need something to carry the sweet sounds of Janelle Monae through the air, through your earbuds, and into your ears.

Deep stuff, right? But that's acoustics for you—the scientific study of sound.

So what do acoustics have to do with sonar? And what does milky coffee and our Spotify playlist have to do with underwater submarine technology?

Everything.

Sonar is an acronym for SOund Navigation And Ranging. We know what you're thinking: how can something so similar to radar just happen to also have a similar sounding name, too? The short answer: it was made to sound the same.

The slightly longer answer: they were so similar that the US Navy decided to give it a similar name. That's exactly the same as the short answer, just in more words, but isn't that how short answer/long answer explanations usually go anyway?

Moving on from the deep, philosophical questions. Sonar uses echolocation in order to find an object. The use of sound to locate and detect objects wasn't invented by people. Animals have been using it for a long, long time. We just happened to notice it and say "Hey, that's weird. Let's study it and see what happens."

So…we did.

Even if we didn't turn it into a science, all sound needs an observer to catch what's produced and hear it—otherwise the sound would disappear into nothingness. It's like that annoying philosophical question about trees falling the middle of the woods. If no one's around to hear them, they don't technically make a sound, no matter how much emotional distress the tree's family feels. By the end of this learning guide, you'll be able to explain why to all of your friends who ask that question. Like a scientist.

You're welcome.

Echolocation is just another extension of that whole processing-sound thing, and many animals, including some humans, have got the process down pat. It wasn't until 1490 that Leonardo DaVinci—yup, the polymath famous for the painting Mona Lisa and inspiring Dan Brown—suggested that a hollow tube could be used to detect ships in an ocean. And with that observation, people began to seriously start thinking about sonar technology.

Sonar can be used to detect and locate things. But…how useful is that? GPS does that automatically.

Believe it or not, there was a point when GPS didn't exist.

Even after Sputnik and the moon landings, we're still using sonar in places a little too wet for electronic GPSes. The Navy uses sonar to make sure that there aren't ships, submarines, or dangerous underwater terrains hanging around where they're trying to go. GPS might be good at traffic monitoring on the highway, but it's terrible underwater.

Trust us; we tried driving to Japan with a GPS. It didn't work.

Besides the fact that there aren't any highways on the Pacific, sonar's just better for water and earth than the GPS's electromagnetic waves. Sound waves propagate (spread over long distances) better in liquids and solids, like water and earth, than electromagnetic waves do. The Navy and many geological agencies use sonar because of that superior spreadage. When you shoot sound waves through water and solids like sand or sunken pirate ships, the sound waves spread out more efficiently, giving much more accurate data.

Sonar doesn't just need to be used in simple materials. A sonar can be pointed upward into the sky to detect aircrafts. It can also be mounted on a satellite to investigate any celestial objects surrounded by plasma. Take that sonar off the satellite and you can even point it down into the earth to find tectonic plates, check for earthquakes, or find landmines.

Sonar isn't limited to military or geological applications. Have you ever felt pukey and wondered which piece of 7/11 sushi caused it? You can get an ultrasound to find out what's going on in your innards. Ultrasound technology is essentially a sonar machine that gives doctors with an image by sending sound waves through—which is a teensy bit less carcinogenic than x-rays. Ultrasound can detect tumors in kidneys, gallstones in the gallbladder, or a swollen appendix in the…appendix.

Oof. Can you imagine a time when they had to cut you open and remove your appendix to see if it was swollen? You can't? That's because they didn't have to.

You can think sonar for that avoided scar later.

Sonar is also used in ocean water conservation, treasure hunting, and fisheries, but the list doesn't end there. Sonar principles and technology have even been used to develop spidey-sense suits to help a blind person sense the environment.

Helping them fight crime will come in release 1.0.1.