Worthington jets are the reason we must live in fear of splashback during all our water-related activities. A small object hitting the water can create a jet of water that shoots up. Here you can see it happening from both below and above the water.

When an object hits the water, the liquid doesn’t always close directly over it. Instead the water will form a crater around the object’s impact. The crater doesn’t last long. As the water rushes back into place, a few drops are propelled up into the air. The drops develop into what’s called a Worthington jet, or a Rayleigh jet. They can shoot up well above the height from which the object was dropped, which is why when we drop a rock into a pool, the resulting splash can soak us.

I find this entire video fascinating. It shows us balls being dropped into water, and the difference in the way the water behaves when the balls are coated with a hydrophobic coating and a hydrophilic coating. If you’re not in the mood to watch for a few minutes, just go to 2:20, which gives us a simultaneous look at the underwater formation of a Worthington jet and its above-the-water splash. It’s the best look available at how these things work.

Top Image: JJ Harrison