When you see a droplet resting on a counter or coalescing around a thread, you don’t generally think of it as a coiled spring, but under the right circumstances that’s what it is. In this video, we can see how the spring releases.
A droplet beading on the floor, or on a spider’s web, looks like a peaceful thing. It may even be peaceful, but that doesn’t mean it isn’t holding energy inside it. If you want proof, edge another drop close to it. When the two water droplets get close enough, they coalesce into one drop. Keep adding water to the droplet and it will eventually collapse from a bead into a puddle.
The hidden energy comes from the surface tension of water—the fact that water molecules adhere to each other to form a skin which holds the rest of the droplet in a sphere. It’s this hidden energy that causes the droplets in this video to hurl themselves off the fiber they’re coalescing on. It doesn’t help that the fiber is coated with teflon, which is hydrophobic, giving the water molecules no way to hold themselves on the web when they’re wiggling around to form a larger drop. Instead, they get catapulted off into space.