Lesson 10 of 16
Marks on a water clock
Show on a big screenA straight jar drains water through a small hole. You mark the water level, its height, every minute. Will the marks be evenly spaced?
Step 1 of 3
- A full straight jar drains through a small hole.
- Marks are made at the level after each minute.
- The marks come closer together as the jar empties.
The idea
No, the marks come closer together as the jar empties.
More water above the hole pushes harder. So water leaves faster.
| Minute | Level (mm) | Fell (mm) |
|---|---|---|
| 1 | 64 | 36 |
| 2 | 36 | 28 |
| 3 | 16 | 20 |
| 4 | 4 | 12 |
| 5 | 0 | 4 |
The rule
A draining jar loses water fast when it is full. It loses water slowly when it is nearly empty. So in a straight jar, marks for equal minutes are spaced unevenly.
Another design was a floating bowl with a tiny hole. It fills and sinks after a fixed time. An Indian bowl took 24 minutes. That time was called a ghati.
Now try it. Slide the minutes. Watch where the marks are placed.
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Try the lab to finish this lesson.