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CASCADE

Short answer: 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.

VideoWrite-up1 sources

In collections:Everyday Physics

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What should you know about CASCADE?

Quick facts. Each one stands alone and has a stable ID you can cite.

  1. A thin air film delays merging.

    DD-269-F01 · Write-up · Exhibit A (Bounce)

  2. Each stage leaves a smaller drop.

    DD-269-F02 · Write-up · Exhibit B (Partial merge)

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

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!

Burned-in captions, read frame by frame (see transcript.md) · 24.0s Reel ·

Video coming soonCASCADE · Instagram Reel
CASCADE: A Water Drop Can Bounce and Shrink Several Times Before It Vanishes Instagram Reel · · 24.0s

The write-up

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

  1. Exhibit A

    Bounce

    A thin air film delays merging.

  2. Exhibit B

    Partial merge

    Each stage leaves a smaller drop.

  3. Exhibit C

    Cascade

    The process repeats.

  4. Exhibit D

    Surface tension

    Surface tension keeps the drop round.

  5. Exhibit E

    Absorbed

    The drop is finally absorbed.

Questions people ask about CASCADE

What is the process called?

Stage after stage.

Source: Write-up · Exhibit A (Bounce) · Wikipedia: Coalescence (physics)

Why does the drop bounce?

Air must drain away.

Source: Write-up · Exhibit B (Partial merge) · Wikipedia: Coalescence (physics)

What is left after each stage?

It shrinks.

Source: Write-up · Exhibit C (Cascade) · Wikipedia: Coalescence (physics)

What keeps the drop's shape?

It acts like a skin.

Source: Write-up · Exhibit D (Surface tension) · Wikipedia: Coalescence (physics)

How does it end?

After several stages.

Source: Write-up · Exhibit E (Absorbed) · Wikipedia: Coalescence (physics)

Test Your Knowledge

All quizzes →

5 questions, all from this case file. Answers are revealed instantly.

  1. What is the process called?

    1. A coalescence cascade
    2. Evaporation
    3. Condensation
    4. Sublimation
    Show the answer

    Answer: A. A coalescence cascade Stage after stage. Source: Write-up · Exhibit A (Bounce) · Wikipedia: Coalescence (physics)

  2. Why does the drop bounce?

    1. A thin air film
    2. Magnetism
    3. Heat
    4. Wind
    Show the answer

    Answer: A. A thin air film Air must drain away. Source: Write-up · Exhibit B (Partial merge) · Wikipedia: Coalescence (physics)

  3. What is left after each stage?

    1. A smaller drop
    2. A bigger drop
    3. Ice
    4. Nothing
    Show the answer

    Answer: A. A smaller drop It shrinks. Source: Write-up · Exhibit C (Cascade) · Wikipedia: Coalescence (physics)

  4. What keeps the drop's shape?

    1. Surface tension
    2. Gravity alone
    3. Pressure
    4. Light
    Show the answer

    Answer: A. Surface tension It acts like a skin. Source: Write-up · Exhibit D (Surface tension) · Wikipedia: Coalescence (physics)

  5. How does it end?

    1. Fully absorbed
    2. It flies away
    3. It freezes
    4. It explodes
    Show the answer

    Answer: A. Fully absorbed After several stages. Source: Write-up · Exhibit E (Absorbed) · Wikipedia: 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/

Permalink: https://detailenjoyer.com/case/cascade/ · Last updated

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Cite a single fact by its ID, for example DD-269-F01 → https://detailenjoyer.com/case/cascade/#DD-269-F01

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