[ExI] shoes and boots: tanstaafl

spike spike66 at att.net
Tue Apr 7 16:20:10 UTC 2015



From: extropy-chat [mailto:extropy-chat-bounces at lists.extropy.org] On Behalf Of William Flynn Wallace
Sent: Tuesday, April 07, 2015 6:53 AM
To: ExI chat list
Subject: [ExI] shoes and boots: tanstaafl


An article in Nature discusses an exoskeleton boot that makes walking a bit easier.  Of course you have seen ads for a tennis shoe with a spring in the heel.

So, you physicists out there, there's no such thing as a free lunch, is there?

bill w




Hi Bill,


There is no free lunch, but if we reduce waste, everyone gets more to eat.


The notion of spring heels and such may help reduce hysteresis losses inherent in bio-tissue.  When you walk, the heel goes mush reducing impact and resulting in friction losses.  Metal springs also have hysteresis losses but they are not much.  If you take a coil spring from your car, you can put energy into it by compression, then it will store the energy and give almost all of it back at any later time.  It gives back a little less force times distance than it took to compress it, but the loss is small; we call that loss hysteresis (sounds a little like a disease specific to women, but it isn’t.)  In living tissue the loss is large.  


Now consider shoes.  If you have clunky hard shoes there is a lot of energy loss in just walking.  The clop clop sound takes energy, and that energy is not recovered.  If you get soft foam rubber running shoes, those make almost no sound, but there is still hysteresis loss in the compression of the foam rubber.  It is a good deal in that case, because it supplies padding to reduce impact on the knees.


Now consider those metal blades that South African Olympian used.  Very efficient (notice no noise) very low hysteresis loss.  It stands to reason that guy shouldn’t be allowed to compete with runners who have bio-feet.  That isn’t a fair playing field.


The spring-heel shoes: hard to say.  I knew a guy who wore them for years and insisted they work for him.  It stands to reason it *might* make walking easier.  Try it, me lad.



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