96 Shhh!-Low

Shhh! FOCUS Question What can people do to control noise?

嘘!人们可以做些什么来控制噪音?

The Problem of Noise Sound tells us a lot about our world. It warns us of danger, lets us hear music, and helps us communicate. But some sounds, such as a leaf blower or an airplane, are simply noise. They are sounds we don't like to hear. Sometimes noise is just annoying, but it can also cause problems. Noise can make it hard to concentrate. Loud noises and long exposure to noise can damage your hearing. Harmful or annoying sounds are called noise pollution.

声音告诉我们很多关于这个世界的事情。 它警告我们危险，让我们听到音乐，并帮助我们交流。 但有些声音，如吹风机或飞机的声音，只是噪音。 它们是我们不喜欢听到的声音。 有时噪音只是令人讨厌，但它也会引起问题。 噪音会让人难以集中注意力。 巨大的噪音和长时间暴露在噪音中会损害你的听力。 有害或恼人的声音被称为噪音污染。

The Science of Sound To reduce noise, it helps to understand sound. Sound begins when tiny particles called molecules move back and forth, or vibrate. These vibrations make the molecules around an object vibrate and create a sound wave. The wave travels outward until it reaches our ears. Sound waves can travel through gases such as air, and liquids, such as water. Sound waves travel faster through water than through air because liquids have molecules that are closer together. The vibrations can quickly transmit energy to surrounding molecules. Sound waves even travel through solids, such as walls. So how can we stop the noisy sounds?

为了减少噪音，了解声音是有帮助的。 当被称为分子的微小粒子来回移动或振动时，声音就开始了。 这些振动使物体周围的分子振动并产生声波。 波向外传播，直到到达我们的耳朵。 声波可以在空气等气体和水等液体中传播。 声波在水中比在空气中传播得快，因为液体分子之间靠得更近。 这种振动可以迅速将能量传递给周围的分子。 声波甚至可以穿过固体，比如墙壁。 那么我们如何才能停止这些嘈杂的声音呢?

Mass Reduces Noise When sound waves hit a solid surface, such as a wall, three things can happen. Some of the waves are reflected, like when you hear an echo off a cliff. Other waves are absorbed into the surface and converted to heat energy. Sometimes, the sound waves travel all the way through the wall. Depending on how they are made, walls can allow sound to pass through easily. But walls with a lot of mass, like thick concrete walls, absorb more sound and keep it from passing through. To make walls thicker, builders attach sheets of dense material, such as drywall. If thick walls have cracks, sound will still sneak in. Sealing cracks in walls helps keep sound out.

当声波撞击固体表面时，比如墙壁，会发生三种情况。 有些波会被反射，就像你听到悬崖上的回声一样。 其他的波被吸收到表面并转化为热能。 有时，声波会穿过墙壁。 墙壁可以让声音轻易通过，这取决于它们的构成方式。 但是质量很大的墙，比如厚混凝土墙，会吸收更多的声音，阻止声音通过。 为了使墙更厚，建筑工人们会在墙上贴一些致密的材料，比如干墙。 如果厚墙有裂缝，声音还是会溜进来。 密封墙壁的裂缝有助于隔绝声音。

Space Reduces Noise Another way to reduce noise traveling through walls is to add dead space—a layer of air between two walls. Sound waves travel through the solid surface, and then slow down, bend, or bounce around in the dead space. This loss of energy keeps some waves from getting through to the other side. Lightweight materials, such as foam and insulation, have many air spaces. They slow down sound and reduce the number of sound waves that reflect off the surface, so you hear fewer echoes. Drapes and rugs also reduce echoes and make a room quieter. Math Moment If 30 of a sound outside your room gets absorbed by your wall. 20 gets reflected. and 15 gets stuck in the dead space, how much of the sound reaches your ears?

另一种减少穿过墙壁的噪音的方法是在两面墙之间增加死空间——一层空气。 声波穿过固体表面，然后在死空间中减速、弯曲或反弹。 这种能量的损失使一些波无法通过另一侧。 轻质材料，如泡沫和绝缘材料，有许多空气空间。 它们降低了声音的速度，减少了从表面反射的声波的数量，所以你听到的回声更少。 窗帘和地毯也能减少回声，使房间更安静。 如果你房间外面的声音有30个被你的墙壁吸收了。 20被反射。第15秒被卡在死区，有多少声音能传到你的耳朵?

Not All Sound is Equal Using materials to reduce the transfer of sound is called soundproofing. But even with soundproofing, you may still hear some sounds Sounds with a lower pitch, like a city bus engine, are harder to block than sounds with a higher pitch, like singing birds. The pitch of a sound depends on its frequency, the number of sound waves that pass a point in one second. High-frequency sounds have a high pitch. Low-frequency sounds have a low pitch. High-frequency sound waves can easily be absorbed or reflected. But low-frequency waves can travel far and do not absorb or reflect easily.

不是所有的声音都是一样的使用材料来减少声音的传递被称为隔音。 但即使有隔音装置，你仍可能听到一些声音，音调较低的声音，如城市公共汽车发动机的声音，比音调较高的声音，如鸟儿的歌声，更难阻挡。 声音的音调取决于它的频率，即一秒钟内通过一个点的声波的数量。 高频声音的音调很高。 低频声音的音调很低。 高频声波很容易被吸收或反射。 但是低频波可以传播很远，不容易被吸收或反射。