In this post we will discuss what amplitude, wavelength and frequency is. But firstly, let’s refresh our memories about the sound itself. Sound is a vibration. Vibration implies that there must be something to vibrate. It is usually an air, but it can be any gas, liquid or even solid. When you clap your hands, you put pressure on air between your hands. This pressure is then passed from molecule to molecule by bumping into each other and moving on in a form of a wave (that is why there is arguably no sound in outer space, if we assume it has no atmosphere, but that is a different discussion…). Such advanced devices as ears can then sense these waves and interpret them.
Ok, so far so good. What do know about waves? Let’s make a small experiment – drop few stones into a water (well, if you are unlucky as me not to live on a seashore, use bathroom). How waves from various stones are different? Well, firstly, waves can be of different height. It is called amplitude. The higher the wave, the more amplitude it has. Higher amplitude means louder sound.
What else do we notice about those waves? When the wave passes through the medium (water, in our example), pressure at this spot oscillates up and down. The distance between 2 neighboring “peaks” of high pressure is called wavelength.
If you had stones of different sizes, there is a chance you saw difference in distance between waves. It means that at any given spot those “peaks” of high pressure can appear at different time intervals. This characteristic is called frequency. It is measured in Hertz, which is simply one oscillation per second.
One can already guess that there is a relation between wavelength and frequency:
Sounds with shorter wavelength have higher frequency and vice versa, longer wavelength mean lower frequency.
When we hear low sounds like bass guitar, it means we hear waves with low frequency and sound of whistle makes an example of waves with high frequency.
Thanks to evolution, our organisms became smart enough not to be distracted by every wave roaming around us. We can hear sounds with frequencies in interval between 20 Hz and 20 000 Hz (or 20 kHz, if you want to make it look smarter) and with age this interval is shrinking.