White noise

白噪音

White noise is a type of noise produced by combining sounds with different frequencies together.

科普時(shí)間：白噪音是由不同頻率的聲音組合在一起，而產(chǎn)生的“噪音”。

Buses are often crowded every day with people going to and from work. Therefore, they are the perfect environment for white noise. They produce consistent noises, like the hum of tires (輪胎) or the purring (嗡嗡聲) of the engine. 

公交車常常擠滿了人——輪胎發(fā)出的聲音，還有引擎聲……這里為白噪聲提供了完美的環(huán)境。

White noise masks distracting sounds and is helpful for people who have trouble getting sleep.

這些聲音掩蓋了一些讓人分心的聲音——這對(duì)入睡有一定幫助。

Rocking motion

在車上搖搖晃晃

Another popular view on why it’s easy to fall asleep on buses is because of the rocking motion. “The motion of buses resembles (像) a mother swaying (搖晃) a baby in her arms. It is very comfortable,” Frankie Chow, founder of Ulu Travel Agency, told The Washington Post. 
關(guān)于為什么在公交車上容易睡著的一個(gè)觀點(diǎn)——因?yàn)樽�在車上�?huì)晃來晃去。“這種搖擺和母親在臂彎里哄睡嬰兒有點(diǎn)類似，讓人感到舒適。”——Ulu旅行社創(chuàng)始人Frankie Chow在接受《華盛頓郵報(bào)》采訪時(shí)表示。

However, it’s not exactly the rocking movement that induces sleep. Rather, it’s the association between rocking and sleeping. If you were rocked to sleep as a baby, you’d associate that rocking motion with going to sleep.

然而，并不完全是因?yàn)榛蝿?dòng)會(huì)讓你犯困——如果你在嬰兒時(shí)期被搖晃著哄睡，你更可能會(huì)把這兩者聯(lián)系在一起。