How a Spill Becomes a Puddle

A little cup tips, and water splashes onto the table. The wet patch grows wider beside the cup. You might wonder why spilled water spreads across a table. The answer starts with the water itself.

Water is a liquid, something that can flow and change shape. When water leaves the cup, it does not stay in one stiff shape. It lands on the tabletop and can move across it.

Gravity is the pull that brings things downward. Gravity pulls the falling water toward the table. After the water lands, gravity keeps pulling downward, helping the tall splash settle into a lower, flatter shape.

The solid tabletop stands in the water's way. The water cannot fall straight through this table. With the table underneath it, the flowing water moves outward across the surface as the spill gets flatter.

A wooden block keeps its own shape when it rests on a table. Liquid water can change shape and flow instead. Which one can spread into a wide, low patch, the block or the water?

The water can spread into that low patch. We call water spread low over a surface a puddle. As this spill moves outward, its puddle becomes wider and shallower, with less water piled up high.

A gentle tilt changes the way the water moves. If one side of the tabletop sits lower, gravity pulls the water toward that lower side. The puddle stretches that way because the water can flow downhill.

On a level table, the spill can spread outward in several directions. On a tilted table, it flows toward the lower side. Different table surfaces let water spread different amounts, so puddles do not all look alike.

Liquid, gravity, puddle. Liquid water lands and flows, gravity pulls down, and the solid tabletop blocks the way below. The water moves outward into a low puddle, or toward the lower side if the table tilts. Spilled water spreads because it can flow and flatten across the table while the table stops it from falling through.

Now you know a little more about the water in your world.