One method of pouring a liquid without spilling it involves holding a small rod, such as chopstick, across the opening over the second container. As the liquid is slowly tipped out, it travels the length of the rod instead of pouring forth or running down the side of the glass.Continue Reading
The surface tension of most liquids, generally water-based, causes it to stick to non-hydrophobic surfaces like the sides of glasses or other containers. Adding a rod across the opening provides a specific path for a slow or moderate stream of the liquid to pour out along. The surface tension clings to the surface of the rod but also follows gravity downwards into the lower second container.
Surface tension is the general phenomenon that causes materials in the liquid state of matter to seek the smallest possible surface area. Additionally, the molecules of a liquid cohere to each other more strongly than the molecules of air surrounding them. This is why a small puddle of water on a flat surface keeps a relatively small surface area instead of spreading out to cover the entire surface. It also describes why free-falling water, such as a droplet out of a faucet, forms a nearly spherical volume, as a sphere has the smallest ratio of surface area to volume.Learn more about Motion & Mechanics