Coffee Spatters Explained

Noel: When I refresh a cup of coffee, I am careful to put the spout of the pot fairly close to the surface of the coffee in the cup to avoid the stream of coffee being accelerated excessively by extra elevation from the cup, thus causing overflow. 

Nonetheless, I get spatters of coffee bouncing out from the close, slowly flowing stream of incoming coffee. 

Has that to do in some manner with surface tension or temperature differential between the cooler coffee in the cup and the hotter coffee from the pot?

Copilot: Ah, the physics of coffee pouring—deceptively simple yet surprisingly complex! What you’re describing likely involves a combination of factors, including surface tension, temperature differential, and even fluid dynamics.

1. Surface Tension: The cooler coffee already in the cup has a stable surface, but when you pour in hotter liquid, it disrupts this equilibrium. Surface tension holds the coffee together momentarily, but the force of the incoming stream can create small disturbances that cause droplets to splash outward.

2. Temperature Differential: The hot coffee from the pot rapidly heats the cooler coffee in the cup upon contact. This sudden temperature change can lead to localized expansion or subtle turbulence, causing tiny jets or bubbles to form—potentially ejecting small droplets.

3. Fluid Dynamics: Even if poured gently, the new coffee alters the movement of the liquid already in the cup. Small waves or eddies form as the new coffee integrates with the old. If the incoming stream breaks the surface in an uneven way, it can create a cascading effect that leads to spattering.

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In a world that has devolved into something so simple that it's terminally boring: a 24-hour stream of inane, irrational, moronic and, sometimes, tactically coy assertions, mostly lies, coupled and intermingled artfully, tit for tat, with policy statements clearly concocted by the Heritage Foundation, my mind wanders to important questions.

I thank Bill Gates for Copilot.

Copilot always has the answer.

To the important questions that we all have these days.