Sound: Here is Why Your Voice Can go Further on a Cold Day

Have you ever been asked, while making a phone call, if you are in a bathroom? Most of the times the caller may be right. Do you ever wonder why the caller may feel you are in a bathroom? It could be you are in a room or hall. But wherever you are there are less furniture/ household items to absorb the sound waves from bouncing off the wall and producing an echo.

I don't know if you have noticed this, but our voice tends to go further during the cold chilly days as compared to the normal. You could hear a pin drop from some blocks away. The same sound travels faster through the warm air.



^{Wikipedia Creative Commons: Sound waves}


As a kid growing up, we didn't have the internet and satellite TVs. So we devised different games that kept us busy. If you had read my earlier posts when I first joined steemit, you would be familiar with some of the games. We invented most of the games we played. However, the game I want to talk about was invented by an unknown person. It involves two tin cans and a string.

We used two empty pasteurised milk tins of which we would cut out one end. We bore a hole in the remaining side of the two cans and connected them with a string preferably a thick, sturdy string.

We did not know, neither did we care, how it worked. But when someone standing on one end said something, the kid on the other side of the "telephone" hears what has been said. That's magic, or so we thought.

But this is what happens with the tin can telephone "magic."

When a kid on one end of the taut string makes a speech, the voice vibrates the air within the first tin, and this vibration travels along the tight line to the other tin and vibrates the air within the second tin such that the child at the end would hear what has been said.

The big question is why didn't we just use the two tin cans separated by a distance to communicate? The answer to this question is the object of this post.

The phrase as quiet as the graveyard shows that whosoever came up with that phrase never visited the outer space. Sound waves could travel virtually in all type of medium, but it can't just get through a vacuum. Unfortunately, (or fortunately, if you are an astronaut who hates noise) outer space is super quiet due to its vacuum nature.

^pixabay

We may be familiar with the speed of light that is 299,792,458 meters per second (m/s) which is usually approximated to 3.00×10⁸ m/s.

Now that brings us to the next question, what is the speed of sound?

My elementary science teacher, who of course is a genius, made us know there is no actual speed of sound. Ok. Hold your horses, what he means is that speed of sound is dependent on the medium that the sound waves are passing through and at what temperature.

The speed of sound in dry air is 343 m/s at 20°C. At the same temperature in water, the speed of sound is 1482 m/s.

The speed of sound changes with a change in medium. That is because sound waves is a pressure wave and have to push through the molecules in the medium it is propagating to get its destination. So its speed is heavily dependent on what the particles are like in the medium of propagation.

The speed of sound could be noticed to be faster in objects with some stiffness, for instance, the speed is more rapid in steel than in wood. It is also quicker in solids and liquids than in gases.

That is why sound travels slower in the air (343m/s) but travels faster in steel (6100 m/s) than in an oak wood (3850 m/s).

The type of medium is not the only thing that affects how sound waves travels as temperature plays a significant role too in its transit through the air. The high humidity reduces the density of air and sound could move faster.

This becomes easier when you recall that density = mass/volume

Water-saturated air due to the high humidity affects the density of air as it is relatively lighter than other constituents of air such as diatomic oxygen and diatomic nitrogen. The more there is water vapour, the more oxygen and nitrogen decreases per unit volume; the air density decreases as it is directly proportional to the mass (which is falling too).

I bet this fact must have spoilt one or two assumptions especially people that feel moist air or humid air is "heavier." I guess this assumption probably came from how difficult it is to breathe moist air compared to the dry air.

The hot air makes air molecules to move faster making it easier for the sound wave, which is a pressure wave, to navigate through the excited air molecules more quickly compared to a slower moving molecule of air that is not heated.

Refraction in light vs Refraction in Sound


The pencil in this clear glass of water appears to be bent due to refraction. The light travels in a straight line, but when it passes through a second medium, the light path bends. What happens is that the speed of light slows down in the water producing the bent pencil phenomenon.

The pencil's bend is toward the air-water boundary due to light being slower in water. The reverse happens when sound waves travel from a slow medium to a fast medium, it reverses; that is bends away from the boundary.

Sound wave propagation behaviour in different medium temperature

During that cold day, if you call out to get the attention of that your dog that is sitting somewhere ahead of you, the sound waves that would have been scattered in all directions would be refracted. This refraction was from the warmer upper layer that is above the cold area near to the ground. This bend on the sound wave downwards makes it travel faster in chilly weather due to above.

If it is during winter time, the snow could also act as a sound absorber, giving you the effect of being in a sound studio or at least a room filled with things free from reverberating sounds.

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^References

^{Moist Air is Less Dense}

^{Nature of Sound}

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