Corner Weights, Spring Rates and a Bruised Foot

[Super_Rich_Bernie]

I rolled the rear wheel of my car over my foot on Friday - which was not too bright.

 

I'm amazed not to have damaged it significantly - it was a little bruised but thats all. An hour later I walked a couple of miles to the pub.

 

Did it withstand the 140kg corner weight of the car?

 

Or is it the spring rate multiplied by the deflection? (my foot is about an inch thick and the springs are the progressive ones) That would be a lot less.

 

Apart from understanding why my foot is OK I may learn something about suspension.

 

Any ideas?

 

Jonathan

[First Man]

Jonathan

 

My guess is that this has something to do with the "camel effect"! A camel has very squashy feet which spread out when the animal steps down to support it on sand. If a camel stands on your foot, it would hurt less and do less damage than, say, a horse, even though both may weigh the same. Your car's tyre would have spread the weight across its surface and, in the absence of sharp edges, I guess that's what saved you. If it had been the metal rim of the whell ... best not to go there!

 

I'm sure Peter Carmichael can explain it much better with a couple of physics formulae.

 

First Man.

[ashaughnessy]

A VW Beetle once drove over my foot when I was at school and it didn't hurt at all.

[Graham Sewell]

It is the old question of force vs pressure. Used to be a standard question at O level about which exerts greater pressure on a victims foot: An elephant weighing 2 tons with a footprint of 0.1m^2 (200,000N/m^2) or a woman weighing 70kg wearing stiletoes with a heel dimension of 0.0001m^2 (7,000,000N/m^2)? The woman will easily break a bone in the victim's foot where the elephant should only leave it bruised. Hence a car tyre is more closely associated with elephant feets in terms of pressure applied by the footprint.

 

Note that I assumed 1g=10m/s^2 in the above calculations!

 

 

 

 

 

Low tech luddite - xflow and proud!

[Jim and Tonic]

Are you volunteering to test your theory Graham?

 

I once pushed mine over my foot too. It got my full attention but no damage.

 

 

 

Jim and Tonic

"Mine's a large one" smile.gif

[Graham Sewell]

Now if I could find a young woman to walk over me in stilettoes....

 

Low tech luddite - xflow and proud!

[Graham Perry]

The elephant and stiletto is a good example. There are many examples of people in the army being run over by tank tracks and getting up and walking away afterwards using the same theory.

My brother has unfortunate practical experience of this. In his youth he fell under the rear wheel of a combine harvester working in a field and was run over from head to foot. He was hospitalised with a broken foot, massive bruising and a fractured scull. It was only because the combine had low ground pressure rear tyres, and the ground was not rock hard that he wasn't killed. The actual load on the tyre was about two tonnes, but spread across a large tyre it wasn't all in one place at the same time. You should have seen the body shaped 'dent' he left in the ground !

 

Edited by - Graham Perry on 25 Jun 2002 07:32:16

[Lauben]

A friend of mine once got his bigtoe run over by a forklift(1500 kg),massive rubber tires, and the stupid git waited two days to see a doctor, worst toe I have ever seen, and that was 4 weeks after the incident. Elephant on stilettos teeth.gif

 

The Slippery Road and Welcoming Ditches Society of 1993