The Fairy-Land of Science · Lecture VI, part 1 · Part 6: Lecture VI: The voices of nature and how we hear them
16. Listening, and how sound travels
Goal: Your child can say that sound needs a shaking (a vibration) and an ear to hear it, and can show that sound travels through string and solid things as well as through air.
You'll need
- A metal spoon (or wire coat hanger) and a piece of string about 3 feet long
- A table edge to tap it on
- Five or six coins or marbles in a row on a table
- Science notebook and pencils
What's in the book
Pages 124 to 129. Buckley starts the second half of the course, about living things. She asks children to listen at an open window in a busy street and on the grass in the quiet country; explains that without ears there would be no sound; hears a poker through a string, through her teeth and through the air; and shows a row of boxwood balls passing a knock along to ring a bell.
The lesson, step by step
Hook: a listening minute
Sit very still for one minute with eyes closed. Then list every sound you both heard.
Read page 125.
Have you ever amused yourself with trying how many different sounds you can distinguish if you listen at an open window in a busy street?
Buckley lists wagons, a whip, street sellers and doors.
SayWe hear all of these at once, and can still tell them apart. How?
Read together
Read pages 126 and 127.
Try some day and prove it for yourself, lie down on the grass in a sheltered nook and listen attentively.
Then her surprising idea:
Strange as it may seem, if there were no creature that could hear upon the earth, there would be no such thing as sound, though all these movements in nature were going on just as they are now.
SaySound needs two things: something shaking, and an ear to catch it.
Try it: the spoon bell
Buckley tied a string to a poker. A spoon is easier. Tie the middle of the string to the spoon handle. Wrap the ends round your fingers and hold your fingertips against your ears (not inside them). Lean over so the spoon hangs free, and let it swing against the table edge. It sounds like a church bell!
Now take your fingers away from your ears and tap it again: much fainter.
SayThe shaking ran up the string straight into your ears.
Try it: passing the knock along
Read pages 128 and 129. Line up five coins touching in a straight row on a smooth table. Slide one more coin sharply into the end of the row. The coin at the far end shoots off, while the others hardly move.
Now imagine these balls to be atoms of air, and the bell your ear.
SayEach bit of air bumps the next, and the bump travels along to your ear.
Tell it back and check
Your child tells back how sound gets from the spoon to your ear. Then ask:
1. What two things are needed for sound?
2. Was the spoon louder through the string or through the air?
3. In the row of coins, which one moved off?
Draw it
Draw a row of little dots (bits of air) between a clapping pair of hands and an ear, with an arrow showing the bump passing along.
Afterwards
Notice it this week: do a listening minute outside, and indoors. Put your ear on a table while someone taps the other end gently: is it louder through the wood?
Tip
Buckley also tried holding the string in her teeth with her ears stopped up. Skip that one; the fingers-on-ears version is cleaner and works just as well.
Answers to the book's problems
1. Something shaking (a vibration) and an ear to hear it. 2. Through the string. 3. Only the coin at the far end; the bump passed through the others.
Worked out for this site from the scan. If a number in your copy differs, trust the book.