I was told this weekend that you can find the weight of a car by multiplying the area of contact the tires make with the ground and the air pressure in the tires. Color me skeptical. I had never heard such a thing.
I was a doubter. I was told the area would be measures in square inches and the pressure in the typical pounds per square inch. Then I thought, area x pressure would then be sq. inches x pounds per square would give you and answer in pounds. So the labels work out, but I was still far from being convinced.
I thought I had a counter proof. What if you put more weight in the car? Then contact area would be greater and I would think the pressure would go up as well. So the car calculations would now be greater. Then I realized I started by making the car heavier, so of course the answer should be greater. So, in trying to disprove this idea, I actually acquire more evidence for it.
I looked online and found that a formula of F = PA or Force = Pressure x Area. (I probably should have remembered that from when I took physics, but that was a while ago.) Since gravity is a force, I'm becoming a little more convinced.
I looked it up online. I literally Googled "tire pressure to find weight of car" and found it. That Google is pretty smart. Anyway, they had a lesson for it. I didn't read it very thoroughly, but it seemed to back up what I had been told. It also said that when done you could check for the actual weight by looking at the sticker inside the driver's door. Well, there is another thing I learned today. I didn't even know there was a sticker there.
It seemed they found the area of a tire and multiplied it by the psi for each individual tire as there could be slight differences from tire to tire. Then they added them altogether.
How does it work out? I don't know. I might try it sometime. Right now the average high temperature is about 35 degrees. If I do spend much time outside, its going to have to be for a better reason than pursuing this. Maybe in the Spring.
How would it work though if I did do it? I know how to find the air pressure. But to find the area? Maybe outline it with chalk? What shape would that be? I'm thinking maybe like a running track with two straight segments and two semicircles. But I'm not sure.
It does seem like an interesting math application and one a class would get into. As a practical matter, probably not. If you really wanted the weight of a care, it seems easier to just check that sticker inside the door.
