Why does water only go one way down the plug hole?

Water does not always travel in only one direction when drained through a plughole. The direction in which water spirals when draining is often determined by the construction of the plumbing system and natural forces. Here's why water typically goes one way down the plughole:

1. Centrifugal Force: When water flows down a drain, it creates a swirling motion due to the conservation of angular momentum. This spinning effect generates a centrifugal force that pushes water toward the sides of the drain.

2. Shape of the Plughole: Most plug holes or drains have a slight curvature or slope that helps guide the water in a particular direction. This slope, combined with the centrifugal force, causes the water to spiral in a preferred direction.

3. Coriolis Effect: The Coriolis effect is a force that arises from Earth's rotation and affects the movement of objects in the Northern and Southern Hemispheres. Although minor in small bodies of water like sinks, it can influence the water's rotation in larger bodies of water like oceans.

4. Local Plumbing Design: The direction in which water spirals can also be influenced by plumbing system design, including the shape of pipes, bends, and any obstacles that may alter the flow of water.

It's important to note that the direction of water flow can change based on geographical location and local conditions. Sometimes, water may change directions or form multiple vortices depending on the specific plumbing arrangement and forces involved.