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Liquid Sand Hot Tub- Fluidized air bed

Mark Rober · demo · Watch on YouTube

Everyday physics & science demos3D printing, CNC & maker projects

What it is

Mark Rober builds a hot tub filled with sand fluidized by air blown from below, so that the sand behaves like a liquid. He explains how fluidized beds work and shows people swimming in them.

Why Hacker News recommends it

HN mentions it as the famous, kid-delighting demo of fluidization, especially in sand battery and industrial process threads.

  • 2 people recommended it
  • 2 different months
  • 0 strong recommendations
  • first 2018, last 2025

What HN commenters said

  1. “I have personally watched kids go nuts over his Fluidized air bed experiments”

    Fun fluidized sand experiment that excites kids about science

    reconbot, 2018-12 · Recommendation · in “What Is Glitter?”

  2. “See this fun fluidized sand-filled jacuzzi”

    Fun demo of fluidized sand behaving like liquid

    isoprophlex, 2022-11 · Recommendation · in “A sand battery could transform clean energy”

Excerpts from Hacker News comments, linked to the originals. Summaries and labels were written by a language model from those comments.

Topics: fluidized bed, mark rober, liquid sand, physics demo, diy build

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