= Impulse versus finite-duration cooling
{title2=$\theta'+a\theta=-F(t)$}
For equal initial temperatures and the same <Newton's law of cooling> coefficient $a>0$, compare a unit <Dirac delta function> cooling impulse at time one with unit-rate cooling on the interval from one to two. The impulse produces a temperature jump of minus one. The finite-duration forcing gives a continuous temperature with change $-(1-e^{-a(t-1)})/a$ while it is active. Relative to the common unforced cooling curve, the impulse contributes $-e^{-a(t-1)}$. Consequently the temperatures cross at $t=1+\log(1+a)/a$, strictly between one and two. After time two the impulse-cooled body is warmer: the later cooling receives less subsequent exponential attenuation.
Back to article page
