Physics trivia

Five things you need to know about sound

There are at least five curiosities about sound that contradict our everyday notions about the characteristics of sound waves.

There are five characteristics of sound you need to know
Some scientific concepts contradict the ideas of what we think is possible. Many phenomena for which we have a logical explanation happen in nature in a totally unexpected way. A good example is the fact that objects of different masses reach the ground together if they are dropped from the same height and air resistance forces are neglected. When this situation is imagined, what we think is logical is that the heaviest object will reach the ground first.

The same occurs with some concepts related to sound waves . The concepts of speed of sound, volume and pitch , for example, have characteristics that challenge our notion of what is possible. Another fact is that some terms that are used daily gain another meaning when applied scientifically.

1. Volume is not related to height

In our daily lives, the terms volume and height are used synonymously, but from a scientific point of view, these two concepts are different.

Pitch is the quality of the sound and is related to its frequency. It allows us to differentiate between high and low sounds. A high-pitched sound has high frequencies, and a bass sound has low frequencies.

Volume is related to sound intensity , which is the amount of energy emitted by a sound source per unit of time over a certain area.

2. We can’t hear too loud sounds!

The human ear has a limitation that prevents it from perceiving sounds of certain frequencies. The range of frequencies audible to humans is for waves of a minimum of 20 Hz and a maximum of 20,000 Hz . Any sound wave that is outside this range is not picked up by the human auditory system .

Imagine a sound source that emits sounds with a frequency of 30,000 Hz. As the pitch is related to the frequency, and the quoted value is outside the human hearing capacity, we can say that the sound from such a source is so loud that it cannot be perceived by a human being.

3. Sound is faster on solids

The closer the molecules are to the propagation medium, the faster the sound waves will be. Therefore, we can understand that the speed of sound in solid media is higher than in liquid media and even higher than in gaseous media.


It is possible to perceive the approach of a train primarily by the sound produced on the tracks than by the air. The sound generated by a locomotive travels through both the air and the tracks. As the rails are in a solid state, sound waves have a higher speed and can be perceived before the waves that propagate through the air.

4. Sound waves cannot be polarized

Polarization is the phenomenon through which a transverse wave, which propagates in different directions, has one of its propagation directions selected by a device called a polarizer. This phenomenon occurs only with transverse waves, which have a direction of propagation perpendicular to the direction of vibration.

Since sound is a longitudinal wave, it has a direction of propagation parallel to the direction of vibration and cannot be polarized.

5. Lightning versus thunder

Instantly after lightning , you can hear the sound of thunder . Thunder arises from the increase in temperature generated by the electrical discharge, which is capable of increasing the temperature of air masses, which expand and collide with cold air masses, generating the characteristic sound of thunder.

Lightning is always perceived before thunder, as the propagation speed of light is much higher than the propagation speed of sound . While light travels at a speed of 300 million meters per second, sound flows through the air at just 340 meters per second.

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