Re: Petential Energy doing Work

On 6/28/2024 2:22 PM, Tom Kunich 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.
 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.
 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.
 Have fun thinking about that.

That's absolute nonsense.
Try coasting at a fairly high speed on a flat, smooth surface, maybe a parking lot. Watch your speedometer as you lean into a sharp curve. You don't increase in speed while in the curve due to any loss in potential energy.
Watch your speedometer again as you exit that curve and go straight. You will not find a significant decrease in speed. That indicates that it's wrong to think the tires were "absorbing" the change in potential energy.
And anyone who thinks Joules are the same as Watts ("320 joules, or if you prefer, watts") knows very, very little about physics.
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- Frank Krygowski