英语时差：在冬季，听声音的季节变换

For those of us who live in the northern part of the country, arguably no other season transforms the environment quite as much as winter. Snow makes the world over so that it's hardly recognizable. The scenery isn't the only thing that changes during the winter season, though. Today's Moment of Science is about how winter transforms the way the environment sounds.

Before that first snowfall, when the ground has hardened from the cold temperatures, sound experiences its first winter makeover. Just as smooth, hard surfaces like glass reflect light, the smoother and harder a surface, the better it reflects sound. The harder ground of the early winter season absorbs less sound. Thus, acoustic waves retain more of their energy when they reflect off the ground. As a result, early winter sounds are louder and clearer. Pay attention, and you might notice that everything sounds a little bit crisper.

After the first snow, sound is made over again. The porousness of snow makes it absorb sound. Specifically, snow tends to absorb higher frequency acoustical waves. As a result, sound becomes quieter and somewhat distorted. Without looking out your window, you might know it snowed simply from noticing how bird calls or passing cars are slightly muffled.

If the snow lingers or it is topped with rain, winter sound will be made over once more. As snow hardens, it becomes smoother, less porous. As you can probably guess, this means that the snow will, like the hardened ground that preceded it, reflect sound well. Sound will once again be crisp and clear.

This winter, see if you can hear how the season transforms sound, as well as the scenery.