Our ears detect this as a less pleasant sensation and often try to screen it out. The trace on the graph is bumpy and random. Noise is produced when the notes aren’t pure. Harmonics are the basis of all musical instruments and result from overlaying pure notes. When we combine pure notes, we can create harmonics. Tuning forks produce a pure sound, one note (a single frequency) and a very smooth line on a graph. When the sound waves form a single sine-shaped wave on a graph, we hear the sound as a pure note. It can refer to any unwanted sound but is more correctly used to describe sound that isn’t rhythmic or pure. (Sound travels at a speed of 343 metres per second in air or 1,484 metres per second in water.) Humans can normally hear sounds between 20Hz and 20,000Hz (20kHz). It is also the same as the number of vibrations per second the particles are making as they transmit the sound.Ī sound of 10Hz means that 10 waves would pass a fixed point in 1 second. For sound, this means the number of pressure waves per second that would move past a fixed point. They relate the intensity of a pressure wave to a normal or standard pressure.įor the human ear in air, the quietest noises we hear are around 10dB whereas sounds of 130dB are considered painful.įrequency is measured in hertz (Hz). This is actually a measure of intensity, which relates to how much energy the pressure wave has. Loudness of sound is measured in decibels (dB). When you show sound waves on a graph, the amplitude is the height of the waves from their middle position and reflects how loud the waves are. This is also related to the maximum distance particles are moved from their normal position as they vibrate, much like how tall the ripples are in the pool mentioned before. Volume (also called loudness) relates to the maximum pressure produced as particles are squeezed together as they are made to vibrate.

We describe the sounds that we hear using several different terms and measure them in different ways.

It is these changes in pressure that can be detected by organs such as the human ear and are sensed as sound.

Pressure increases when particles are squeezed together and reduces when they move apart. These changes in particle spacing are also changes in pressure. Similar to water ripples, pressure waves move outwards from the sound source. The effect is very much like dropping a stone into a pool of water and causing a ripple pattern (sound waves) extending outwards from the original source (your clapping hands). The particles close to your hands are pushed outwards and bump into neighbouring particles, and these then move and bump into more particles. This effect ripples out and away from your hands as a small group of sound waves. When you clap your hands, you force air particles together and then apart.

A high pitch sound has