The Fairy-Land of Science · Lecture III, part 3 · Part 3: Lecture III: The aerial ocean in which we live
9. Air pushes up, weighing the air, and the wind
Goal: Your child can show that air pushes up as well as down, can say that a barometer weighs the air, and can explain that wind is air rushing in to fill the space left by warm air rising.
You'll need
- A small plastic cup or glass, water, and a square of stiff card (an index card)
- A sink or tray to work over
- A drinking straw and a glass of water
- Optional: a ribbon or strip of tissue for a wind flag
What's in the book
Pages 63 to 72. The card that stays on an upside-down glass of water; water held up in a U-shaped tube; the mercury barometer that weighs the air; what wind is and why the sun makes it blow (sea breezes by day, land breezes at night, the trade winds); and the air that spreads light into shady corners and makes the stars twinkle.
The lesson, step by step
Hook question
SayIf I turn a full glass of water upside down, what will happen?
Your child will say it spills. Buckley says there is a way to stop it.
Try it: the card on the glass
Work over the sink. Fill the cup to the very top, lay the card flat on it, hold the card on with your hand, and turn the whole thing over. Now gently take your hand away.
But no! the card remains as if glued to the tumbler, kept there entirely by the air pressing upwards against it.
If it falls, just try again: a full cup and a flat card work best.
Try it: water held up by air
Put the straw in the glass of water, press a finger tightly on the top, and lift it out. The water stays in the straw! Take your finger off and it falls out.
SayWith your finger on top, no air can push down from above, but the air below pushes up and holds the water. Buckley's U-shaped tube works the same way.
Weighing the air
Read or tell pages 64 to 67. A barometer is a glass tube with a heavy liquid metal, mercury, held up about 30 inches by the push of the air. When the air gets lighter, the mercury falls, and rain may be coming.
Safety: mercury is poisonous. Never touch it or play with an old barometer or thermometer that has some in it. Today most barometers have no mercury.
What is wind?
Read pages 67 to 69.
Wind is nothing more than air moving across the surface of the earth
The sun warms the ground, the ground warms the air, and warm air rises. Cooler air rushes in to fill the space, like children rushing out of a crowded room when the door opens. At the seaside, the land warms faster by day, so the breeze blows in from the sea; at night it blows the other way.
If it's breezy, take the ribbon outside and see which way the wind blows. (Buckley mentions lighted paper going up a chimney; never do that.)
Tell it back and check
Your child tells back what makes the wind blow. Then ask:
1. What held the card on the glass?
2. What does a barometer measure?
3. At the beach on a sunny afternoon, which way does the breeze blow?
Twinkle, twinkle
Read the end of page 71.
If it were not for our aerial ocean the stars would stare at us sternly, instead of smiling with the pleasant twinkle-twinkle which we have all learned to love as little children.
SayThe moving air makes the starlight shimmer. That's why stars twinkle.
Afterwards
Notice it this week: which way the wind blows each day (a flag, smoke from a chimney, leaves). On a clear night, watch the stars twinkle.
Tip
Do the card trick over a sink or outside. The point is the surprise; a few spills are part of the fun.
Answers to the book's problems
1. The air pressing up against the card. 2. The weight (pressure) of the air. 3. From the sea toward the land, because the land is warmer and its air is rising.
Worked out for this site from the scan. If a number in your copy differs, trust the book.