Do they really come from Sweden, or from elsewhere?

Which Olympic Games had the largest attendance and how many tickets were sold?

Which states from the United States of America have multiple time zones?

Like absentmindedly drumming on a tabletop, idly running a finger around the rim of a glass can make a kind of music—an otherworldly, ghostly music. How come?

Even if your family groans when you sing along to the car radio, even if you didn’t make the cut for the choir, and even if you got asked to be the drummer rather than the lead vocalist in your friends’ garage band, you sound exactly like your favorite pop (or opera) star in the shower. How come? And why do we enjoy singing in the shower to begin with?

There’s an official name for the horrible sounds that emanate from a blackboard: chalk squeal. Scientists say that the explanation involves both friction and resonance.

When you hold a large seashell to your ear, you can hear a distant roaring sound. It’s as if the great rumble and crash of the ocean waves is somehow trapped within the shell. So when you bring a seashell home from the beach, it keeps the memory of the sea alive.  But even if you don’t have a seashell handy, and it’s too cold to go to the beach, you can always hear the ocean. Just pick up an empty coffee mug, and hold it to your ear, tilted slightly away. Ah, there it is—the gentle, echoing roar of the waves.

Have you ever stood on a city sidewalk and heard the distant wail of an approaching fire engine? As the fire truck comes into view, the sound of its siren becomes louder and more frantic, the wail higher and higher pitched. Then, as it passes, the opposite effect occurs: The sound of the siren drops in pitch, getting lower and lower as the vehicle vanishes into distant traffic. But the fire truck’s driver hears no such change; to him, the siren that he flipped on 20 blocks ago has sounded at a steady pitch.

We’ve all seen it in movies or old TV westerns—as the stagecoach (or train) picks up speed, its fast-moving wheels appear to switch direction, slowly turning backward. We also occasionally see the phenomenon in real life, with spinning car tires and whirling ceiling fans. Scientists call it the Wagon-Wheel Effect. What causes the “backward” effect?