Why a Record Sings

The record player broke one day, and Irishka needed to listen to records. She sat there with her lips pouting. So Tanya said to her:

"Look at the record through a magnifying glass."

Irishka took the record and examined it through the magnifying glass.

Tanya asked:

"Do you see the tiny grooves?"

"I see them."

"Are they straight or do they have curves?"

"They have curves," answered Irishka.

"Well, does the needle run smoothly along the wavy groove, or does it start to vibrate?"

"Probably it vibrates."

"And if it vibrates, then..."

"It squeaks..." Irishka smiled.

Tanya took a paper megaphone and stuck a sewing needle into the tip. Then she put the record on a pencil:

"I'll spin the record, and you hold the megaphone."

Tanya spun the pencil, and the record spun on the pencil. Irishka took the megaphone and placed the needle on the record, and the record started singing: "Little bird, where were you? Where did you build your little nest?..."

It's hard to spin the record evenly - it spins sometimes faster, sometimes slower, and so the song sounds funny - sometimes high-pitched like Pinocchio, sometimes deep like a bear. When Irishka heard such funny sounds, she started laughing, and her mood immediately improved.

Try the experiment with a record, pencil, and megaphone with a needle. Try spinning the record at different speeds. Why does the sound come out sometimes high, sometimes low?

---

The experiment with playing a record is very simple. It's only important not to forget that this method can damage regular short-playing records. Long-playing records are easily damaged by a sewing needle or pin. Besides, the width of the groove on a long-playing record is small, and the sewing needle immediately sits on two grooves. So that the megaphone can easily and freely follow along with the needle on the groove, you need to hold it by the very edge at the top. If you spin the record on a pencil, it's very difficult to achieve uniform rotation and the sound "floats." You can also do this same experiment by spinning the record on the turntable of a record player, but still producing the sound with a needle and megaphone.