There is a reason why most objects surrounding us seem to generate sound. Running water, wind, cell phones, and voices are all examples of sounds that you hear on a daily basis and understanding the basics of sound is best achieved by getting familiar with sound waves.
The noises you hear around you are waves that travel through a medium such as air or water. These waves produce vibrations that run longitudinal to the direction they are travelling in, meaning that there is a back and forth motion happening in the direction they are travelling in.
A great example of how soundwaves work is when a smartphone receives a text message from a sender.
In this instance, the smartphone contains a diaphragm, which is a piece of cone-shaped material that has electronics inside designed to make the diaphragm move back and forth when it receives a text message.
During this movement, the atoms and the molecules in the air surrounding the diaphragm create a soundwave that works to spread out in a mini explosion. Physicists in the past have described soundwaves in terms of the movement of their particles in the air.
This movement has been defined as a Displacement Wave, which causes the surrounding air to expand and compress, while spreading outwards.
Soundwaves can be described as pressure waves because devices have been built to detect those changes in pressure.
Devices such as microphones use a diaphragm to sense soundwaves that create areas of high or low pressure that causes the diaphragm to vibrate. The electronics in the microphone uses this vibration to translate the soundwaves into audio.
As humans age, they lose specific cells that work to detect sound. This results in the eardrums losing the ability to detect higher pitched soundwaves.
Dog whistles create higher soundwaves with frequencies that humans cannot hear. These frequencies are known as Ultrasonic frequencies.
The measurement of sound is measured through units known as Decibels.
Ambulances continuously emit soundwaves at a certain frequency through a siren. As the ambulance approaches you, the siren creates more soundwaves that are higher in pitch. The pitch of these soundwaves will decrease as the ambulance moves away from you and this occurrence is known as the Doppler Effect.