Can you see the waves the strings make after you strum the guitar? Normally strings vibrate so fast that you cannot see them. So why can you see them now?
Against the black background of the drum, you cannot see the black strings. You only see them when a white line passes, producing a series of separate “pictures”. Your brain combines them into one smooth movement, discarding the black, “empty” images. As a result, you see the strings moving more slowly than in reality.
Also try to tighten the strings with the pedal. They will vibrate even faster and sound higher.
Vibrations of your voice
You also make a sound by vibrating your vocal cords. In boys, the vocal cords grow longer. This makes them vibrate more slowly and the tone of their voice becomes lower. This is how ‘their voice breaks’.
Vibrations in your ears
Vibrations propagate in the air and reach the eardrum in your ear. This thin layer of skin also starts to vibrate and transmits those vibrations all the way to your inner ear. There, it converts the vibrations into signals, which are sent to your brain. This is how you hear sound!
Vibrations of blue whales
These impressive animals make sounds that we cannot hear. Blue whales have a special kind of vocal cords, that can vibrate very slowly. Therefore, the sounds are too low for human hearing.
These low-pitched sounds also travel very far in the water. They can talk to each other up to 1,000 km away. At least, if there are no large ships in the vicinity. These ships make a lot of noise, preventing blue whales from hearing each other.