Path: ...!eternal-september.org!feeder3.eternal-september.org!news.eternal-september.org!.POSTED!not-for-mail From: AMuzi Newsgroups: rec.bicycles.tech Subject: Re: Bicycle physics question Date: Thu, 20 Jun 2024 08:07:05 -0500 Organization: Yellow Jersey, Ltd. Lines: 147 Message-ID: References: MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit Injection-Date: Thu, 20 Jun 2024 15:07:05 +0200 (CEST) Injection-Info: dont-email.me; posting-host="01696b91a8232badada2e48108ecaff6"; logging-data="2717340"; mail-complaints-to="abuse@eternal-september.org"; posting-account="U2FsdGVkX18/2H8KAkKUYNdI7zyXtJNG" User-Agent: Mozilla Thunderbird Cancel-Lock: sha1:n8HQU/Eqw/6FNfon3tjLP8mlraU= Content-Language: en-US In-Reply-To: Bytes: 7342 On 6/19/2024 9:52 PM, Jeff Liebermann wrote: > On Wed, 19 Jun 2024 22:39:07 -0000 (UTC), wrote: > >> Jeff Liebermann wrote: >>> On Tue, 18 Jun 2024 00:16:01 -0000 (UTC), 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. >>> >>> >>>> 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 >>> >>> >>> 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: >>> >>> >>>> 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? > > Oops. It should be "can't". Unfortunately, it's also 1/2 wrong. One > CAN use potential energy to do work, but the work isn't done until > after things start to move. This article sorta fumbles through the > concept: > "Is potential energy and "work done" the same thing?" > > >> Potential energy can certainly do work, think of a trebuchet. > > Notice the word "can". Yes, potential energy can do work, but no work > is done until the trebuchet starts to move. For an exercise in > frustration, try calculating the amount of work done by an object that > isn't moving. Work = force * distance_traveled. If the distance > traveled is zero, no work is done. > >> Potential energy is lost in leaning. > > True. None of that potential energy goes into moving the bicycle > forward (or backwards). Easy enough to test: > Dismount from your bicycle. Jam the wheels against something that > keeps the bicycle from moving sideways. Grab the top tube. When you > lower or raise the top tube, do you feel any force the might move the > bicycle forward or backwards? You shouldn't. Therefore don't expect > leaning the bicycle over to gainfully contribute to forward or > backward movement. > >> Tom thinks it's going into tire friction, > > "Tom thinks" is an oxymoron. > >> 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.. > > Before the discovery of quantum theory, it was axiomatic that if it > can't be detected or observed, it doesn't exist. Fortunately, nobody > has invented a quantum bicycle. > >> Maybe Tom's right. Front tires on motorcycle certainly wear faster >> on twisty roads, even at low (35 mph) speeds. > > Tom is certainly politically to the right. > > When you turn the motorcycle handlebars on a twisty road, you feel > quite a bit of resistance to turning. The motorcycle wants to > continue going forward in the direction of travel and your turning the > front wheel tries to convince it to go not in a different direction. > The resistance to the turning force causes the tires move slightly > sideways. Going sideways is highly abrasive and causes tire wear > through friction. A side effect of the tire wear is heat or energy > loss. > >>>> "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... > > Apology accepted. I've been trying to keep the math at a very simple > level or totally avoid the math by using gedankenexperiment (thought > experiments) and analogies. When I start using anything more complex > than basic arithmetic, I instantly lose half my audience. > >> Thanks for writing, > > You're welcome. > >> bob prohaska " Work = force * distance_traveled. If the distance traveled is zero, no work is done." Yes, that's right. Losses from tire scrubbing are extant in two wheelers but significant in four wheel vehicles. -- Andrew Muzi am@yellowjersey.org Open every day since 1 April, 1971