Akustik
8 cards from across every topic, each citing a source. Tap one to open it in the feed.
- A kettle is loudest just before it goes quiet.
At the bottom the water reaches 100 degrees while the top is still at 70. Steam bubbles form there, rise into cooler …
- A whip crack is a sonic boom.
The whip does not crack because it hits something. A wave runs from handle to tip, and because the cord keeps getting …
- Counting seconds tells you how far away the storm is.
Sound moves through 20 °C air at about 343 metres per second; light arrives practically instantly. When you see …
- Helium doesn't raise your pitch. Seriously.
With helium in your lungs, your vocal cords vibrate at exactly the same rate, so the pitch stays put. But sound travels …
- How a bat catches a mosquito in pitch darkness.
The bat calls in ultrasound, depending on species between 11 and 212 kilohertz, well above your hearing. From the delay …
- How headphones erase noise by producing more sound.
A microphone on the headphone measures outside noise. A chip calculates what part would reach your ear and plays …
- The siren never changes its pitch. You just hear it differently.
As an ambulance approaches, it squeezes its sound waves together: they arrive more densely and the tone sounds higher. …
- Underwater, sound travels more than four times faster.
In air at 20 °C, sound covers 343 metres per second. In fresh water it is 1,481 m/s, in seawater about 1,500 m/s. The …