Wednesday
Wednesday: Build Lab, String Around Everything
Raven lines up the can and three lids on the Blueprint Table, smallest to biggest. "Build Lab. Every round thing gets measured."
"String around, then straight across," Rocket says. "Then divide. I predict a little more than three every time."
"Predict, then measure," Raven says. "And measure twice. String stretches if you pull it."
Rocket wraps the small lid. "15.8 around, 5 across." Raven writes it down. "What do you notice before you divide?"
"Three fives are 15. It is a bit more than that," Rocket says. "Same as the can."
Nova hovers over the row of lids, her light moving from small to big. "Four circles, four answers," she says. "Compare them when you finish."
Your mission
Measure the circumference and the diameter of four round things. Divide each circumference by its diameter.
If pi is the same for every circle, all four answers should land near 3.14.
- An empty can with a smooth rolled rim, and three round lids of different sizes.
- A piece of string about a meter long, and a ruler or tape measure.
- A marker, masking tape, and your Blueprint Book.
Lids are plastic or smooth metal. A grown-up checks every edge before you measure.
String is for measuring only. It stays on the table and away from children under three and pets.
- Wrap the string once around the can. Mark where the end meets the string.
- Lay the string flat along the ruler. Read the length to the mark: that is the circumference.
- Measure straight across the top, through the center. That is the diameter. Measure it twice.
- Write both numbers in a table. Divide the circumference by the diameter.
- Repeat for each lid. Compare the four answers.
The crew's lab table
These are the crew's own measurements from the Blueprint Table, in centimeters, written in Raven's Blueprint Book.
| Round thing | Diameter (cm) | String around (cm) | Around ÷ across |
|---|---|---|---|
| the can | 8 | 25.2 | 3.15 |
| the small lid | 5 | 15.8 | 3.16 |
| the medium lid | 10 | 31.5 | 3.15 |
| the big lid | 12 | 37.6 | 3.13 |
Every row lands between 3.13 and 3.16. The string never lands exactly on 3.14, because string stretches and marks are thick.
The formula predicts the can at 3.14 × 8 = 25.12 cm. The crew measured 25.2. Close enough to trust the formula.
- Read the question.
- Tap your answer.
The medium lid has diameter 10 cm. Using 3.14 for π, what circumference does the formula predict, in centimeters?
The big lid has diameter 12 cm. What circumference does the formula predict, in centimeters? (Use 3.14 for π.)| From the lab | True or false? |
|---|---|
| Every row of the crew's table divided to a little more than 3. | ? |
| A bigger circle gives a bigger answer for around ÷ across. | ? |
| 3.14 × 5 = 15.7 | ? |
Four circles, one number. Tomorrow the crew cuts a circle into wedges to find the area inside.