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Bike Shop 3-5 / Week 05 / Wednesday
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Week 05 · Gears and the Chain

Wednesday

Model chain drive
// Counting teeth to predict turns
⏱ about 15 min

Wednesday: Model Chain Drive

Rocket finds two jar lids and a rubber band. "A chain drive, homemade!"

He stretches the band around both lids and turns one.

The other lid turns too!

Raven marks each lid with a dot. "What do you notice when the dots go around?"

Nova hovers low. "Try lids of two sizes," she says. "Watch which dot goes around more."

A model of the chain

Scientists build models to study real things.

A rubber band can stand for the chain.

Round lids or thread spools can stand for the gears.

Turning one lid pulls the band, and the band turns the other lid.

  1. Find two round lids or spools of different sizes.
  2. Put a dot on the edge of each one with a marker.
  3. Ask a grown-up to stretch a rubber band around both.
  4. Hold the lids on a table, a little apart.
  5. Turn the big lid slowly, one full turn.
  6. Count how many times the small lid's dot goes around.
Safety first
A grown-up stretches the rubber band.
Keep rubber bands away from faces and eyes.
Turn slowly so nothing snaps.
Hands stay clear where the band meets the lid.
Which lid I turnedTurns I madeTurns of the other lid (my count)
big lid1
small lid1

What the model shows

In the model, the band carries the turning from one lid to the other.

On a bike, the chain carries the turning from front to back.

A smaller back gear turns more times than a bigger front gear.

MODEL MATCH-UP
  • Read the question.
  • Tap your answer.
In the model, what stands for the chain?
What do the lids stand for?
Turn the big lid once. What does a smaller lid do?
StatementTrue or false?
A model can help us study a real thing.?
In the model, the rubber band is like the chain.?
A small back gear turns fewer times than a big front gear.?
WHY THIS EXERCISEThe small back gear turns more times, just like the small lid.
BUILD THE MODEL
  • ?Find two lids of different sizes.
  • ?Mark a dot on each lid.
  • ?A grown-up stretches a band around both.
  • ?Turn the big lid one full turn.
  • ?Count the turns of the small lid.
WHY THIS EXERCISEFind, mark, connect, turn, then count.

Marvelous model making! Tomorrow we find out how gears help on hills.

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