Mrs. Wilson leaves her freshly-baked blueberry pie on the windowsill to cool. The delicious fragrance diffuses through the air with a diffusion coefficient of D = 0.2 cm 2 /s .
a) How long does it take for Dennis to smell the pie in his tree house 10 meters away?
b) Is the answer to (a) realistic? Based on your experience, how long does it typically take for a smell to travel this distance (you might have experienced this, e.g., at an outdoor barbeque)? What physical effect is missing from our calculation?