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Matt2matt2002:
Have I discovered something new?
On my usual 17 miles whiz around the lanes of South West Scotlandshire today, I was on a long straight stretch with a slight downward gradient.
Don't ask why but for some reason I took both legs off the pedals, raised both legs outwards away from the frame, swung them backwards and then forwards. I immediately felt the bike "rush" forwards!
(I didn't feel the bike slow when my legs went backwards)
Any physicists out there who can put me right on what happened?
If I had kept doing the swing thing would I have kept going forever?  :D

Danneaux:

--- Quote ---If I had kept doing the swing thing would I have kept going forever?
--- End quote ---

<Psst!  Matt!>  This is confidential, but the answer is...
.
.
.
.
...yes!

But don't tell anyone, or they'll never sell another bicycle with drivetrain, economies will collapse, and the world as we know it will end.


--- Quote ---Have I discovered something new?
--- End quote ---

Ehm, not "new", per se...the knowledge has been around for ages, but suppressed, and for very good reason.

All the best,

Dan. (...who's scared to death of what happens when this becomes common knowledge...)

Danneaux:
Oh, drat!  The word has already gotten out, Matt. Perhaps this explains the current state of the world economy.

At any rate, you may find the information at the following link related to "dynamic weight transfer" and the concept of "dynamic wedge" to be of interest in light of your own experience:

http://www.ozebiz.com.au/racetech/theory/wttrans.html

Best,

Dan. (...exploring my "off-the-grid" options as I write this...)

Matt2matt2002:
Thanks for the link.
Very interesting but (I'm) stupid.  ::)
I couldn't spot anything about sticking your legs out the side of racing cars.

Is it a perceived effect? Did I spend energy swinging my legs backwards and then perceive the forward motion?
Perhaps because I was having a free ride down hill at the time, and this combined with the energy I had spent, I felt the forward motion amplified?

I suspect you have the answer to this (for me) conundrum.
I usually abide by the KISS principle, so,please enlighten me and keep it simples.  ;)

Danneaux:

--- Quote ---...Very interesting but (I'm) stupid...
--- End quote ---

No, Matt, you're no stupider than me, or we're both stuck at the same level of stupitude.

I spent the last hour trying to model this behavior and finally gave it up as too complex and with too many variables to do accurately. All my old physics formulae apply to conservation of angular momentum and such, and this is a linear problem having to do with the conservation of energy and forward momentum. In the interests of time and getting something (anything!) else done today, I've got to admit temporary defeat (though my mind will keep working at it).

What I think is happening is this (and, yes, I got intrigued enough to get the bike out and try it out in the street in front of my house. By this time, the neighbors think I'm nuts for being so interested in bikes anyway, so there's little to lose; they probably figure it's just a continuation of my downward spiral...):

= The bike and your collective mass have forward momentum.

= When you swing your legs back, that counters the forward momentum to a degree, but to move your legs back, you're also propelling your body forward.

= When you swing your legs forward, the forward transfer of their mass (what, maybe 20kg or so?) is additive to the greater mass of yourself and the bike (a seeming gain), but swinging your legs forward propels your upper body back, so that would cancel out.

I don't yet have my bike computer hooked-up to the Nomad, but I would imagine any speed gained by swinging your legs forward would be cancelled by swinging them back. It would be neat to see if there is a momentary gain/loss in speed, but I can't imagine any net-total gain in forward momentum resulting from swinging your legs.

Sadly, I think it is a perceived effect. I think you called it exactly when you opined...
--- Quote ---Perhaps because I was having a free ride down hill at the time, and this combined with the energy I had spent, I felt the forward motion amplified?
--- End quote ---

Perhaps our friend and colleague JimK can save us with a timely and cogent analysis. I'm guessing if anyone can, it is he.

All the best,

Dan. (...proving the neighbors right one Bicycle Venture at a time...)

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