# CASCADE (DD-269)

> When a drop of water lands gently on a pool, a thin film of air can keep it from merging at once, so it appears to bounce. It then partly merges, leaving behind a smaller drop, and this repeats in what is called a coalescence cascade until the drop is fully absorbed. Surface tension holds each drop's shape between the stages. The footage is a slow-motion lab recording of a drop falling from a needle.

- Department: Science (also Nature)
- First published: 2024-07-11
- Last updated: 2024-07-11
- Permalink: https://detailenjoyer.com/case/cascade/
- Author: Marcus Easterling (DetailEnjoyer), The Detail Department

## Quick facts

- **DD-269-F01**: A thin air film delays merging. _(Write-up · Exhibit A (Bounce))_
- **DD-269-F02**: Each stage leaves a smaller drop. _(Write-up · Exhibit B (Partial merge))_

## Write-up

A water drop can bounce and shrink several times before it vanishes. Each bounce leaves behind a smaller daughter drop.

1. **Bounce**: A thin air film delays merging.
2. **Partial merge**: Each stage leaves a smaller drop.
3. **Cascade**: The process repeats.
4. **Surface tension**: Surface tension keeps the drop round.
5. **Absorbed**: The drop is finally absorbed.

## Related case files

- [Is Water Sticky? (DD-296)](https://detailenjoyer.com/case/is-water-sticky/): I linked more water physics

## Reel vs. record

- **Note**: None needed.

## Video: CASCADE: A Water Drop Can Bounce and Shrink Several Times Before It Vanishes

- Duration: 24.0 s · Published: 2024-07-11
- File: https://detailenjoyer.com/assets/videos/C9S9jlByd0p.mp4

### Transcript

Did you know, when water falls onto the surface of a much larger body of water, it can appear to bounce and shrink before being completely absorbed? This phenomenon is due to what's known as the coalescence cascade. Initially, surface tension causes the drop to maintain its shape and bounce on the surface. As the drop loses energy, smaller droplets break off and merge with a larger body. The drop gradually shrinks through successive coalescence events until it is fully absorbed.. NOW YOU KNOW!

## Questions & answers

**Q: What is the process called?**  
A: Stage after stage. _(Source: Write-up · Exhibit A (Bounce) · Wikipedia: Coalescence (physics))_

**Q: Why does the drop bounce?**  
A: Air must drain away. _(Source: Write-up · Exhibit B (Partial merge) · Wikipedia: Coalescence (physics))_

**Q: What is left after each stage?**  
A: It shrinks. _(Source: Write-up · Exhibit C (Cascade) · Wikipedia: Coalescence (physics))_

**Q: What keeps the drop's shape?**  
A: It acts like a skin. _(Source: Write-up · Exhibit D (Surface tension) · Wikipedia: Coalescence (physics))_

**Q: How does it end?**  
A: After several stages. _(Source: Write-up · Exhibit E (Absorbed) · Wikipedia: Coalescence (physics))_

## Sources

- [Wikipedia: Coalescence (physics)](https://en.wikipedia.org/wiki/Coalescence_(physics))

## Cite this case file

Easterling, Marcus. "CASCADE." The Detail Department (DetailEnjoyer), case file DD-269, last updated Jul 11, 2024. https://detailenjoyer.com/case/cascade/