Re: 'Backwards' bikes

On Mar 10, 8:51 am, Simon Brooke <si...@xxxxxxxxxxxxxx> wrote:
dkahn400 wrote:
On Mar 8, 9:28 pm, Simon Brooke <si...@xxxxxxxxxxxxxx> wrote:

So you apply the sideways force to the saddle, which is easy.

Which of course does not affect the common C of G of bike and rider.

Not if you ignore momentum, no.

Is this momentum created from nothing, or is it pre-existing sideways
momentum? The former appears to contravene the laws of physics while
the latter seems to describe a lean that is already occurring without
any input from the rider. Because you could explain a bit.

Except you can do it from stationary without ever touching the ground, or
anything else (apart from the seat of the swing). Try it!

Yes, I know. I don't understand why you think it's necessary to touch
the ground with your foot in order to get a reaction force from it.
The frame of the swing is touching the ground,

As are the wheels of the bike.

True, but now I'm more confused than ever about your position. You
seemed to be saying that starting a swing from nothing was an example
of moving the C of G relative to the ground without a reaction force
from the ground. Now you seem to be saying that the mechanism by which
a swing gets moving is comparable to the way a bike is leaned.

When the child uses her muscles to move her C of G relative to the
frame of the swing, the swing wants to move the other way but it can't
because it is rigidly fixed to the ground. When a rider uses his
muscles to move his C of G sideways relative to a bicycle, the bicycle
is free to pivot about the axis of the line joining the centres of the
two contact patches. The two systems are therefore not analagous.

--
Dave...
.

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