What happens when your production budget consists of water, soap, food colouring, and maybe a bit of magnetic goo? If you're the filmmaker responsible for this music video, the result is a beautiful demonstration of fluid dynamics, fingering flows, drips, and bubbles.

Top image: Screenshot from the music video, "Jack and the Giant."

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The fluid dynamics behind this trippy video are surprisingly straightforward to create such beautiful effects. Filmmaker Kim Pimmel used water as his base, a fluid with effectively the same viscosity and density as food colouring. As a result, the dye flows freely, mixing and spreading in fuzzy blurs. For visual contrast, Pimmel adds drops of soap, tiny "bubbles" that do not mix with the surrounding water. To keep things from getting too repetitive, he also uses ferromagnetic fluids โ€” fluids with iron filings that both colour them black and make them responsive to magnetic fields.

What I love about this video is that despite clever editing and higher-quality camera work than I could personally emulate at home, all of the science is cheap, easy, and safe to do as a lazy weekend indulgence in the wonders of fluid dynamics. To make it even more interesting, try using milk as the base layer. A higher fat milk will have the greatest density difference so the dye will float at the surface, while the fatty liquid's surface tension is broken by even a small droplet of soap, leading to dramatic overturning effects.

Tip via the always-excellent Physics Today Facebook page.

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