Tire-Exponential Decay

You have a hole in your tire.  You pump it up to P=400 kilopascals (kPa) and over the next 60 minutes it goes down till the tire is quite flat. What exactly is the “law” that governs this slow decrease in pressure? We build a conceptual model of the mechanism behind the model and decide that this is a process of exponential decay. To test this conclusion, we do an experiment with a car tire and check that the rate of decrease of pressure is indeed proportional to the pressure itself.  This activity contributes nicely to our understanding of exponential change.