There are only a handful of smartphone components the average user cares about, and the list usually starts with the processor, battery, and screen. While virtually no one thinks about niche sensors like a gyroscope or proximity sensor, they’re some of the most important parts of your device. They power key features that you don’t even realize, such as when your screen orientation auto-rotates or when your screen goes black after pressing a phone against your ear for a call.
Aside from these vital features we take for granted, your smartphone’s sensors double as hidden tools you can use to solve daily problems or test real-world experiments. Third-party apps like Physics Toolbox or Phyphox unlock these tools, allowing you to deploy them however you’d like. I tested it myself, and I couldn’t believe that my smartphone could use Sonar — yes, that Sonar — to identify the distance of objects using the speed of sound. With two phones, you can even gauge how fast sound waves travel using Phyphox’s Acoustic Stopwatch tool.
Both Sonar and Acoustic Stopwatch are completely free in the Phyphox app — here’s how you can try the clever physics experiments for yourself.
Use Sonar to measure distance
Send out an audio chirp to determine how far away an object is
Sonar stands for sound navigation and ranging, and it works by sending short bursts of sounds that are then reflected by a physical object in your environment. Since you know the speed of sound is roughly 340 meters per second, you can gauge the distance of that object by measuring the amount of time it takes for the sound to bounce back. Your phone has a speaker and microphone, so it can emit a “chirp” that is then reflected by environmental surfaces and detected by the mic when it returns. The amount of time this takes, when multiplied by the speed of sound and divided by two, indicates the distance of an object.
For the best results, you need a controlled environment. If you simply use a smartphone in a random room, the emitted chirps will reflect off of every nearby service, returning an imperfect result. You want as little environmental noise as possible, and you can create this environment by building a shield to block unwanted reflections. A homemade shield with common household items could include foam packaging, couch cushions, or clothing.
Finally, you need a reflecting object — like a plate — to point at the phone’s speaker and microphone. Use the shield to surround the phone in every direction but the one facing the reflector.
Then, open the Phyphox app and start the Sonar experiment. You want to position your phone within the homemade shield, so the app only picks up the echoes and reflections you are trying to record. A live distance graph will show peaks as the app emits the chirping noise. The app does the calculations for you, representing the result as a distance graph, rather than a time graph. You can move the reflecting object closer or further away and watch the app calculate the unique distances across multiple tests.
Try using an acoustic stopwatch to measure sound
With two phones and a tape measure, you can pinpoint the speed
To measure the exact speed of sound, you’ll need to use Phyphox’s Acoustic Stopwatch feature. Essentially, it works with two phones and a tape measure to pinpoint the speed of sound waves. Acoustic Stopwatch starts when it detects a loud enough sound, and stops when it detects a second sound of similar loudness. So, place two phones a certain distance apart, and measure exactly how far away they are from each other.
Then, start the Acoustic Stopwatch test. Make sure that environmental noise isn’t accidentally starting or stopping the stopwatch by raising the audio threshold level. Then, when background noise isn’t triggering the stopwatch, begin the test. With one person beside each phone, clap one at a time. The first clap will start the stopwatches, while the second clap will stop them.
The trick is that the first clap will start the first phone before the second, and the second clap will stop the second phone before the first. You’ll get two different measured times on the two phones. The delay between each phone can be calculated by dividing the distance between the phones by the speed of sound. Using that figure, you can multiply the distance between the phones by two, and divide the result by the delay you just calculated. This will give you the exact speed of sound.
It’s a clever math and physics experiment that only requires two phones and a tape measure. If you’re confused at all, I’d recommend watching the Phyphox videos on YouTube above. The team behind the free app does a great job at demonstrating how it all works in real-world tests.
Everything else you can do with Phyphox
It’s the secret to unlocking the hardware sensors in your phone
After trying these tests for yourself, you’ll demonstrate how a smartphone (or two) can be used to measure the distance of objects and calculate the speed of sound. It’s a really neat demonstration, as most of us come up with an image of deepsea exploration when we think of Sonar. Yes, your smartphone can make use of Sonar, too — although it may be tricky to get an accurate reading. And, with the Acoustic Stopwatch, you can measure the time between two acoustic events and calculate the speed of sound using the result.
These implementations of Phyphox are just the beginning. You can also use the app to try out smartphone sensors including light, proximity, gyroscope, magnetometer, and many more. It’s completely free, and lets you use the sensors you’ve never realized were inside your device.
- OS
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iOS, Android
- Price model
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Free
- App Type
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Physics sensor experiment app
Phyphox is a free mobile app that lets you tap into your smartphone’s hardware sensors for real-world physics experimenting. The app was developed at the 2nd Institute of Physics A at the RWTH Aachen University. It supports using the accelerometer, magnetometer, gyroscope, pressure, microphone, proximity, and GPS sensors.