Crazy pool vortex

TL;DR

When a plate is dragged through still water, it creates half-ring vortices that move across the pool without dissipating, forming dark spots due to the lens-like shape created by the balance between gravity, centripetal forces, and surface tension.

Transcript

[SQUEAKING] [POP] Check this out. I'm just gonna drag this plate through the water in the pool. That's it. But look what forms-- perfect black circles on the bottom of the pool. And it's so weird. They don't die. They just keep going right next to each other. I sped this footage up because the circles took 3 minutes to cross the pool and didn't see... Read More

Key Insights

• 💁 Vortices are circular movements in fluids formed by a difference in fluid speed.
• 💦 Half-ring vortices are formed when water is forced to move around an object, creating connected dips on the water's surface.
• 😋 Half-ring vortices stay together because they are connected at the ends, forming a half vortex ring.

Questions & Answers

Q: What are vortices and how are they formed?

Vortices are circular movements in gas or liquid. They are formed when there is a difference in fluid speed, creating a shear force that starts the fluid spinning.

Q: Why do the half-ring vortices stay together?

The half-ring vortices stay together because they are connected at the ends. The movement of water around the whole plate creates a curved vortex line, resulting in a half vortex ring.

Q: Why are half-ring vortices rarely seen?

Half-ring vortices are rarely seen because they occur on the boundary of two media. Most vortices either close into a loop or end at a boundary, making half-ring vortices less common.

Q: How do the dark spots form in the water?

The balance between gravity, centripetal forces, and surface tension creates a funnel-shaped lens. This lens focuses sunlight away from the center, creating a dark circle surrounded by a bright ring.

Summary & Key Takeaways

• Moving a plate through the water forms little vortices, which are gas or liquid moving in circles, caused by a difference in fluid speed.

• The vortices are able to travel across the pool without dissipating due to their angular momentum and only lose energy through friction.

• The half-ring vortices are formed when water is forced to move around the plate, creating connected dips on the water's surface.