Sound · Pulse Beat
Sound is a vibration that travels through a material as a wave of pressure. It needs something to move through, so there is no sound in empty space.
Sound is a vibration that travels through a material as a wave of pressure. It needs something to move through, so there is no sound in empty space.
In air at 20 °C sound travels at about 343 m/s. It is faster in water (about 1,480 m/s) and faster still in steel. That is why you see lightning first and hear thunder later: counting the seconds and dividing by three gives the distance in kilometres, roughly.
Frequency (in hertz) is how many vibrations per second, and we hear it as pitch. Humans hear about 20 Hz to 20,000 Hz. Amplitude is how big the vibration is, and we hear it as loudness.
The Doppler effect is the change in pitch when a source moves: an ambulance siren sounds higher as it approaches and lower as it leaves, because the waves bunch up in front and stretch out behind.