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Earth and Space 6-8 / Week 06 / Wednesday
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Week 06 · A Disk of Dust and Gas

Wednesday

Sky Deck Lab: A disk in a bowl
// How a spinning cloud became a solar system
⏱ about 20 min

Wednesday: Sky Deck Lab: A Disk in a Bowl

Rocket fills a wide clear bowl with water on the Sky Deck table and sprinkles in a pinch of sand.

"Now I am gravity and spin at the same time," he says, and stirs the water in slow circles with a spoon.

The sand grains swirl. Every grain travels the same direction around the bowl, and they settle toward the middle.

"What do you notice?" Raven asks. "Did any grain go the other way?"

Rocket watches hard. "No. Every one follows the spin. And look, they are gathering in the center."

Nova hovers over the rim. "Your model moves grains with water, not gravity," she says. "What does it still show truly?"

Your mission

Today you make a spinning disk in a bowl and watch how loose grains behave inside it.

The stirred water stands for the spinning cloud. The grains stand for dust. The center of the bowl stands for where the Sun formed.

You will record the direction each grain moves, where the grains gather, and whether the spinning water stays flat.

  • A wide, clear bowl or a large clear jar, filled two thirds with water
  • A pinch of clean sand, or small torn bits of paper if you have no sand
  • A spoon for stirring
  • A tray or the kitchen sink to work over, and a towel for spills
  • Your Sky Log and a pencil
Safety first
Work over a sink or tray. Wipe up spills right away so no one slips.
Keep sand away from your eyes and wash your hands when you finish. Nothing goes in your mouth.
Ask a grown-up before borrowing a bowl, and carry water with both hands.
  1. Fill the bowl two thirds with water and let it settle until the surface is still.
  2. Sprinkle a pinch of sand or paper bits across the surface. Watch where they go with no stirring. Record it.
  3. Stir in slow steady circles for five seconds, then lift the spoon out. Watch the grains for twenty seconds.
  4. Record the direction the grains travel. Record whether any grain goes the other way.
  5. Record where the grains gather as the water slows. Record whether the surface stays flat while spinning.
  6. Let the water stop. Stir the other way and repeat. Record what changes.
TrialDirection of stirDirection grains movedWhere grains gatheredSurface flat?
No stirnone
Stir 1
Stir 2
PREDICT, THEN CHECK
  • Read the question.
  • Tap your answer.
Before you stir: in which direction will the grains move?
What in the real solar system matches the grains gathering toward the center?

What the model gets right and wrong

Right: everything in a spinning disk goes the same direction. That matches the planets all orbiting the Sun the same way.

Right: the spinning water keeps a flat top. The real disk was flat too, which is why the planets orbit in nearly one plane.

Wrong: the water moved your grains. In the real cloud, gravity did the pulling and the cloud spun on its own as it shrank.

Wrong: your grains all ended up in the center. In the real disk, some material stayed out and clumped into planets.

ONE STIR, START TO FINISH
  • Tap a card.
  • Then tap its spot.
1First
2Second
3Third
4Fourth
Model claimTrue or false?
The stirred water stands for the spinning cloud.?
Grains in a spinning disk move in many different directions.?
In the real disk, gravity did the pulling.?
In the real disk, every bit of material ended up in the Sun.?
WHY THIS EXERCISETesting a model against the real system is how scientists decide what it can and cannot explain.
Try this
Stir faster, then slower. Does the surface dip in the middle more when it spins fast? Record what you see.
Drop one grain at the very edge during a spin. Does it join the others in direction? Record it.
Draw your bowl from above with arrows showing the grains' direction. Beside it, draw the solar system from above with arrows for the planets.

Careful observing. Tomorrow you read a NASA table to see just how flat the real disk left the planets.

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