Re: Petential Energy doing Work

On Fri, 28 Jun 2024 18:22:39 GMT, Tom Kunich <cyclintom@yahoo.com>
wrote:

Using Pogacar as an example let's say that normal upright riding puts his CG 1.5 meters abovr the ground. Simple Triganometry will tell us that the CG at 45 degrees lean is .707 that of his uptight position. (I have seen him lean more thn 45 degrees.) This makes a change in potential energy of 1.5 m x 0.707 = 1.06 m. Or about a change in CG of 0.44 meters.
>
As an estimation, Pogacar and bike weigh 166 lbs or 75 kg. The change in potential energy from upright to a 45 degree lean for a corner is 1100 joules upright and 780 leaned over or a change in energy in the bike structure of 320 joules, or if you prefer, watts. In a frictionless world this would cause the bicycle to accelerate as it leaned. But this is not a frictionless world and what happens is that much of this 320 watts is pushed into the tires and absorbed by the friction in the tires resisting the centrifugal force and holding the tires to the ground.
>
The physics are clear and well understood even though there seems to be quite a bit of misunderstanding on the group. Andrew thinks that the change has something to do with the CG to the tire's contact patch. That is not the change in energy but the direction of the force resisting the cenptrifugal forces.
>
Since a rather hefty 320 watts are added to the energy simply by lowering the CG in a gravity field you can more understand why a bike in a turn may seem to slide out from under a rider so rapidly. Once the tires break traction there is no counter action against the increased energy. This should also give you a much greater appreciation of just how much traction to spare the sides of the best tires have over the use of it while upright and not braking.
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Now to be correct we have to remember that in order to be able to corner at 45 degrees, you have to be going at such a speed that on flat ground you would be pouring 700 or 800 watts into the pedals and so the addition at this speed is some 40% of a small number since very little energy is absorbed into the tires if you are not accelerating or braking. But the tires absorb is all resisting the centrifugal forces. Under normal contitions the upright bike's tires only absorb a significant amount of energy while accelerating or braking. And pro-level riders can and do commonly apply 1400 or more watts into acceleration.
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And since you are forced to stop pedalling at that angle of lean, the 700 or 800 watts are reduced to the 320 which are added through the change in potential energy.
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Have fun thinking about that.

Tom, you are correct that potential energy is measured in Joules.
However, everything else you wrote is wrong:
<https://en.wikipedia.org/wiki/Joule#Watt-second>
<https://www.studocu.com/en-us/messages/question/2856280/the-formula-for-potential-energy-is-pe-m-g-h-in-this-formula-pe-stands-for-potential-energy>

You wrongly declared:
"...a change in energy in the bike structure of 320 joules, or if you
prefer, watts."
Joules are equivalent to watt-seconds, not watts.  Joules can also be
converted to ergs, eV (electronvolts), gram calories, food calories,
BTU (British Thermal Units), horsepower-hrs, tons of TNT, or
kilowatt-hrs, but not to watts.  Your speculation which follows is
based on this misunderstanding and is also wrong.  More:
<https://en.wikipedia.org/wiki/List_of_conversion_factors#Energy>

There are a variety of "work, energy and power" cheat sheets
available.  Pick one and study it:
<https://www.google.com/search?q=work+energy+power+cheat+sheet&tbm=isch>

You claim that if you lower and raise your bicycle, by tilting it from
upright to -45 degrees
"...a rather hefty 320 watts are added to the energy..."
Swell, where does energy go?  Does the bicycle frame change from hot
to cold as it goes up and down?  Where is this rather large amount of
potential energy stored, absorbed or dissipated?  It's not stored in a
change in elevation as potential energy because that's what you just
used to raise and lower the bicycle.  Think about it and check your
assumptions.


--
Jeff Liebermann                 jeffl@cruzio.com
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