Newton’s law of cooling states that the temperature difference between a hot body and its surroundings decays exponentially:

T(t)Tamb=(T0Tamb)et/τ.T(t)-T_{\text{amb}}=(T_0-T_{\text{amb}})\,e^{-t/\tau}.

Example — A cooling coffee

A coffee at 90°C90\,°\text{C} in a room at 20°C20\,°\text{C} with τ=10min\tau=10\,\text{min}: after 20min20\,\text{min} it is at 20+70/e229,5°C20+70/e^2\approx 29{,}5\,°\text{C}.

Topics: Exponential function
Concepts: Exponential decay · Euler’s number
Functions: Exponential function
Skills: Modelling · Using formulae
People: Isaac Newton