This past weekend my tire pressure light in my car went on.
I told a friend with me who was in the car who told me this was normal for cars
in the winter and not to worry about the light. As I am from somewhere in
California, where it is not often below 60 degrees F in the winter, I had no
prior experience with this (this is my first year having my car here). This can
be explained by physics by using the Guy-Lussac’s law – that P

_{1}/T_{1}=P_{2}/T_{2. }Here volume remains the same, as no gas was lost, assuming there are no holes in any of my tires.
My tires were last filled to about 32 psi earlier this
summer, so I will estimate the temperature to be 80 degrees F, or 300 K. 32 psi
converts to 2.20 x 10

^{5 }Pa. This weekend when I noticed the light was on, it was about 28 degrees F or 271 K.
If we plug this into the equation we get:

(2.2 x 10

^{5 }Pa)/300K = P_{2}/271K
P

_{2}= 1.98 x 10^{5}Pa or 28.7 psi.
This decrease from 32 to 28.7 psi explains why the tire
pressure light turned on.

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