Estimate the depth of a pit by timing a dropped rock.
Time from dropping the rock until you hear the impact. Sound travel time is subtracted.
Tap Start when you drop the rock, Stop when you hear the impact.
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| Time (s) | Depth (see) | Depth (hear) |
|---|---|---|
| 1 | 4.9 m | 4.8 m |
| 2 | 19.6 m | 18.6 m |
| 3 | 44.1 m | 40.7 m |
| 4 | 78.5 m | 70.5 m |
| 5 | 122.6 m | 107.4 m |
| 6 | 176.6 m | 151.1 m |
| 7 | 240.3 m | 201.0 m |
| 8 | 313.9 m | 256.8 m |
| 9 | 397.3 m | 318.1 m |
| 10 | 490.5 m | 384.6 m |
Visual timing: Depth = ½ × g × t², where g = 9.81 m/s².
Acoustic timing: The measured time includes both the rock falling and the sound traveling back up. The total time T = tfall + depth / vsound. Substituting depth = ½ × g × tfall² and solving the quadratic gives the actual fall time.
The speed of sound is assumed to be 336 m/s (air at 8 °C, typical for caves).
This assumes free fall with no air resistance. For deep pits (> ~80 m), air resistance on a small rock becomes significant and the actual depth may be less than calculated.