Science Articles

Sound: Are All Vibrations Audible?

The movement of a particle away from its fixed position, also known as mean position, and the return of that particle back to its mean position is known as one vibration.

All bodies are made up of tiny particles. These particles are always vibrating, however small the vibrations may be.

The movement of a particle away from its fixed position, also known as mean position, and the return of that particle back to its mean position is known as one vibration. Particles complete one vibration in a matter of milliseconds. Imagine how many vibrations one single particle produces in a minute!

A body is made up of thousands of such particles and these tiny things work together to produce vibrations in the whole body. One can’t even process how much of slog that is for such miniscule specks residing in the colossal galaxy.

When bodies vibrate, they produce sound which is then heard by us. The fascinating thing is the fact that all of this happens within a matter of seconds.

When a body is struck by an outside force, its particles produce vibrations, causing the whole body to produce vibrations, which then causes the air around us to vibrate and ultimately reach our ears as sound.  And the best part is, we don’t even realise how much happened in our surroundings just to make sure we hear the sound.

We also don’t realise that there are tonnes of other vibrations constantly occurring around us, the sounds of which we do not hear.

Frequency and the Types of Vibrations on the Basis of Frequency:

The number of vibrations produced by a vibrating body in one second is called frequency. Its working unit is Hertz (Hz).

The human ear is capable of registering sounds that fall between a frequency of 20Hz and 20000Hz only. This frequency limit is called the hearing limit.

If the frequency of vibrations is between 20Hz and 20000Hz, they are called sonic vibrations, which are easily perceived by us.

There are two other basic important vibrations among tonnes that do not have a frequency which is within the hearing limit.

Infrasonic vibrations, as the name suggests, have a frequency that falls below that of the sonic vibrations. They have a low frequency of 20Hz or less which cannot be distinguished by human ears. Fishes and dogs, though, can hear them. Now we know the science behind dogs having an excellent hearing ability. They can perceive the feeblest sounds.

The vibrations that exceed the limit of hearing also cannot be heard by us. They are called ultrasonic vibrations. They have a high frequency that exceeds 20000Hz. Animals like bats and dolphins can emit and hear these ultrasonic vibrations. These help them to protect themselves and also to search for prey. Bats are nocturnal animals that use these vibrations to manoeuvre at night.

Ultrasonic Vibrations: A Gift to Mankind

Though humans can’t hear ultrasonic vibrations, they can be perceived and emitted by various machines. The machines that emit ultrasonic vibrations have proven to be an amazing catalyst to the industrial revolution.

  • In the medical department, ultrasonic vibrations (emitted and perceived by ultrasound machines) are used for the imaging of internal organs of the human body.
  • Ultrasonic vibrators cause distress in cockroaches and mice and are used to drive them away from warehouses.
  • They are used in dishwashing machines. These vibrations cause detergent particles to vibrate against the utensils, thus rendering them clean.

Apart from this, these vibrations are also used by fishermen, for relieving pain in joints and for homogenising milk.

Despite discovering so much about vibrations, there will always be lots we don’t yet know.