Physics Question #117

Harry Pritchard, a 65 year old male from the Internet asks on January 11, 2000,

How can I find out whether it takes more effort (work by pump) to increase the air pressure in a tire from 60psi to 80psi if the tire is under maximum load than when it is under no load at all?

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The answer

John Jones answered on January 11, 2000

The answer can be deduced from basic physics, I doubt there have been any experiments on it, though.

It can be proved mathematically that if the rubber of which the tire is made obeys Hooke's Law (that is, if the extension of the rubber when a force is applied to it is proportional to the force, which is approximately true for most materials), then the work needed to increase the tire pressure from p1 to p2 is the same whatever the load is on the tire.

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