Re: Bicycle physics question

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Sujet : Re: Bicycle physics question
De : <bp (at) *nospam* www.zefox.net>
Groupes : rec.bicycles.tech
Date : 20. Jun 2024, 00:39:07
Autres entêtes
Organisation : A noiseless patient Spider
Message-ID : <v4vmmb$25qk1$2@dont-email.me>
References : 1 2
User-Agent : tin/2.6.2-20221225 ("Pittyvaich") (FreeBSD/14.0-RELEASE-p6 (arm64))
Jeff Liebermann <jeffl@cruzio.com> wrote:
On Tue, 18 Jun 2024 00:16:01 -0000 (UTC), <bp@www.zefox.net> wrote:
 
While out for a motorcycle ride this morning a question
applicable to both bicycles and motorcycles came to mind:
>
When a bike/cycle is leaned into a turn, its center of gravity
is lowered.
 
Gravity doesn't move.  However, your center of mass does move and is
lowered.
<https://en.wikipedia.org/wiki/Center_of_mass>
 
That would seem to remove some potential energy.
 
True, but it's a tiny amount of energy.
 
Potential_energy = mass * gravity * height
or
joules = kg * 9.8 meters/sec^2 * meters
 
Notice that it's the same change in potential energy whether you're
moving of standing still.  You could be riding furiously or at a
traffic light, and the change in potential energy would be the same.
Your forward motion is also not involved in the potential energy
calculation, because it is perpendicular to force vector (gravity).
 
If you were to lean the bicycle over 1/2 meter and you and your
bicycle weigh 80 kg (176 lbs), the change in potential energy would
be:
Potential_Energy(change) = 80 * 9.8 * 0.5 = 392 joules or 392
watt-seconds
>
<https://www.omnicalculator.com/physics/potential-energy>
I like calculators that allow me to mix metric and imperialist units.
 
To undo the lean, the wheels have to be steered back under
the CG, which requires pedal effort on the bicycle and extra
throttle on the motorcycle.
 
Correct.  Assuming 100% efficiency (most of which is lost in
compressing the tires), in the above example, you will need to supply
392 joules of energy to return to an upright position.  Note that the
energy is supplied only in the upright direction (perpendicular to the
ground) and does not involve anything in the forward direction. 
 
There are some interesting comments in this discussion:
<https://www.bikeforums.net/advocacy-safety/288303-what-makes-bike-turn.html>
 
But, leaning a bike/motorcycle doesn't seem to make it go
perceptibly faster, so if it takes work to stand it back up,
where did the energy of leaning over go?
 
It didn't go anywhere.  It's all POTENTIAL energy, not kinetic energy.
You can use potential energy to do work.  Only kinetic energy can do work.
       ^
     can't <-typo?
Potential energy can certainly do work, think of a trebuchet. Potential
energy is lost in leaning. Tom thinks it's going into tire friction,
we all seem to agree the amount is smallish compared to the KE of
the bike and dissipation caused by air drag making it hard to detect..

Maybe Tom's right. Front tires on motorcycle certainly wear faster
on twisty roads, even at low (35 mph) speeds.

"The epitome of futility is the analysis of velocipedes with z
wheels, where z is a complex number..."
 
That's true only on a rough road, where the velocipede can move in the
Z direction (up and down) going over the bumps.  The z axis is also
involved in making a turn, where z component of the centripetal force
keeps the rider and bicycle from falling over.

In the context of the original joke z=x+iy, where i is the
square root of minus one. Apologies for the obscurity...

Thanks for writing,

bob prohaska


Date Sujet#  Auteur
18 Jun 24 * Bicycle physics question50<bp
18 Jun 24 +- Re: Bicycle physics question1John B.
18 Jun 24 +* Re: Bicycle physics question46Jeff Liebermann
20 Jun 24 i`* Re: Bicycle physics question45<bp
20 Jun 24 i +* Re: Bicycle physics question40Frank Krygowski
20 Jun 24 i i+* Re: Bicycle physics question14AMuzi
20 Jun 24 i ii+* Re: Bicycle physics question2<bp
25 Jun 24 i iii`- Re: Bicycle physics question1<bp
21 Jun 24 i ii+* Re: Bicycle physics question2Jeff Liebermann
22 Jun 24 i iii`- Re: Bicycle physics question1AMuzi
21 Jun 24 i ii`* Re: Bicycle physics question9Frank Krygowski
22 Jun 24 i ii `* Re: Bicycle physics question8Frank Krygowski
22 Jun 24 i ii  `* Re: Bicycle physics question7Catrike Ryder
25 Jun 24 i ii   `* Re: Bicycle physics question6Frank Krygowski
25 Jun 24 i ii    `* Re: Bicycle physics question5Zen Cycle
25 Jun 24 i ii     +* Re: Bicycle physics question2Jeff Liebermann
25 Jun 24 i ii     i`- Re: Bicycle physics question1Zen Cycle
26 Jun 24 i ii     `* Re: Bicycle physics question2John B.
26 Jun 24 i ii      `- Re: Bicycle physics question1Zen Cycle
20 Jun 24 i i`* Re: Bicycle physics question25zen cycle
20 Jun 24 i i +- Re: Bicycle physics question1AMuzi
20 Jun 24 i i `* Re: Bicycle physics question23Frank Krygowski
20 Jun 24 i i  `* Re: Bicycle physics question22AMuzi
20 Jun 24 i i   `* Re: Bicycle physics question21Frank Krygowski
21 Jun 24 i i    `* Re: Bicycle physics question20AMuzi
21 Jun 24 i i     +* Re: Bicycle physics question4Catrike Ryder
21 Jun 24 i i     i`* Re: Bicycle physics question3AMuzi
21 Jun 24 i i     i `* Re: Bicycle physics question2Catrike Ryder
21 Jun 24 i i     i  `- Re: Bicycle physics question1AMuzi
21 Jun 24 i i     +- Re: Bicycle physics question1Jeff Liebermann
21 Jun 24 i i     `* Re: Bicycle physics question14zen cycle
21 Jun 24 i i      +- Re: Bicycle physics question1Frank Krygowski
22 Jun 24 i i      +* Re: Bicycle physics question5AMuzi
22 Jun 24 i i      i`* Re: Bicycle physics question4Frank Krygowski
23 Jun 24 i i      i `* Re: Bicycle physics question3AMuzi
24 Jun 24 i i      i  +- Re: Bicycle physics question1Frank Krygowski
26 Jun 24 i i      i  `- Re: Bicycle physics question1Jeff Liebermann
22 Jun 24 i i      +* Re: Bicycle physics question6zen cycle
24 Jun 24 i i      i+* Re: Bicycle physics question4AMuzi
24 Jun 24 i i      ii+- Re: Bicycle physics question1Zen Cycle
24 Jun 24 i i      ii+- Re: Bicycle physics question1Zen Cycle
24 Jun 24 i i      ii`- Re: Bicycle physics question1Jeff Liebermann
24 Jun 24 i i      i`- Re: Bicycle physics question1Jeff Liebermann
22 Jun 24 i i      `- Re: Bicycle physics question1Jeff Liebermann
20 Jun 24 i `* Re: Bicycle physics question4Jeff Liebermann
20 Jun 24 i  +* Re: Bicycle physics question2Frank Krygowski
20 Jun 24 i  i`- Re: Bicycle physics question1Ted Heise
20 Jun 24 i  `- Re: Bicycle physics question1AMuzi
20 Jun 24 `* Re: Bicycle physics question2Doc O'Leary ,
20 Jun 24  `- Re: Bicycle physics question1Jeff Liebermann

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