The Bathtub Analogy | AI Learning Guide

We often imagine the ocean draining into a giant hole at the center of the Earth, much like water going down a bathtub drain. But this intuition is misleading. To understand why oceans stay put, we first have to dismantle this 'drain' analogy and look at how gravity actually works on a planetary scale.

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The Intuitive Trap

When we see water swirl down a sink or a bathtub, our brains form a powerful mental model: water flows down because there is a hole at the bottom, and gravity pulls it into that void. It is natural to assume the Earth works the same way—that the ocean is just a giant pool of water waiting to drain into a massive hole at the planet's center. However, this analogy breaks down immediately when we look at the actual structure of the Earth and the nature of gravity itself.

Key Question

If gravity pulls everything toward the center, why doesn't the ocean simply fall through the crust and disappear?