Why does coffee spill when you walk?How fluid dynamics fight your every step

From the show

Science Around You

Walking with a full mug feels like a high-stakes balancing act because standard cup sizes interact poorly with human biomechanics. The natural oscillation of liquid in a mug matches the frequency of an average stride, creating a resonance effect that amplifies waves until they breach the rim. Understanding this mismatch reveals that spills are often a matter of physics rather than simple clumsiness.