Not all Blocks are Frictionless, nor Springs Massless

I recently was in a situation where I realized my theoretical physics knowledge was subtly working against me, in a real-world situation.

Let me begin by saying I've been having really bad luck with tires recently. Maybe it's because I drive about 2 hours each weekend to visit my fiance, and it adds an unusual amount of wear and tear on my tires, I don't know. What I do know is that in the past year or two, I've been forced to replace a tire 4-5 times. It was only a few weeks ago, when I got a flat and had to replace the most recent 2 tires that it was apparent enough for the particular repair place I was near to tell me this is NOT due to running over something on the road, etc. In short, the tire was just destroyed from the inside out, probably due to improper pressure in the tires. I had been driving on under-inflated tires, probably for quite some time.

Under-inflated? I didn't get it. Aren't tires air-tight? Where would the air go, if it's a closed system. Now, I'm the first to admit I'm a car idiot. My mechanic knowledge goes about as far as adding oil, adding gas, and replacing a flat tire with a spare (I've gotten REALLY good at that part in recent years, in fact). So when I asked the mechanic how often I should be checking the pressure of my tires, myself, he suggested once a month.

Once a month. So slightly more often than "check the pressure, how do you do that?"

Needless to say, I bought a pressure reader display thingy and as soon as I got home from the mechanic, I checked the pressure on my tires. The two they replaced were exactly what the label on the tire said it should be, 44 PSI. One of the back tires was at 35 PSI. The other back tire was at something like 22 PSI, nearly HALF deflated. I very promptly went to the nearest gas station and filled them with air to the correct pressure.

So apparently, tires are not a PERFECT, ideal system. Air can, in fact, leak out over time, so that a perfect 44 PSI tire today might not stay that way indefinitely.

Welcome to the world of masses with friction, springs with mass, and objects that are not perfect spheres. It's a scary place.