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trying to get the math down but that darn apples & oranges crap as well as bogus info even within a formula is holding me back. i have this INCORRECT kinetic energy formula to start with,

that's OK though, the 10 CUBED can just be ignored and just multiply 215.9 by 1.356 to get the proper 292.72 instead of 292720.Using "engineering" units, convert mph to fps, multiplying by 22/15: 55 mph = 80 . Divide weight (in pounds) by 32.174 to get mass in slugs. Substitute these values in formula above; you should get 215.9 × 10³(10,000???!!!)ft lb.(215900???? formula calls for 215.9 x 1 to get 292.72 result!)Finally, convert to J, multiplying this by 1.356 J/ft lb. I get 292.72 kJ.

215.9 x 1.356 = 292.7604kj actually. they didn't even multiply their own numbers correctly DESPITE the erroneous cubing.

so, after wading through the nonsense to get to the allegedly CORRECT formula for how many kj are needed to push 2135 lb @ 55mph, the math becomes USELESS anyways because another online conversion utility says that 300kj (rounded up from 292) = just 83w!!! there's no way that can be right. even if the three erroneous 0s you get from cubing 10 are added back to the mix to get 300,000kj, the conversion becomes 83,000w which can't be right either. the math is seriously busted in one or both places.

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6,653 Posts

After you have stopped gibbering try - LEARNING TO READ!

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7,793 Posts

Hey zero,

Do you ever read replies to your posts?

major

after wading through the nonsense to get to the allegedly CORRECT formula for how many kj are needed to push 2135 lb @ 55mph, the math becomes USELESS anyways because another online conversion utility says that 300kj (rounded up from 292) = just 83w!!! there's no way that can be right.

velocity (v) and mass (M) relate to energy in the form of kinetic energy (KE) or energy associated with motion, by the formula KE = ½Mv².

Watts (W) are the units for power. We all know what time is and the units are seconds (s). Any type of energy has the units of joules (j) which are defined as watt seconds (Ws). So KE = Ws.

One Watt of power is equivalent to one Joule of energy expenditure per second. It may require 300 kJ of energy to accelerate a car to 55 mph but that would generally depend on the amount of time taken to do the acceleration. Once you're moving, maintaining a given speed is dependent on your friction and drag losses, and requires a certain rate of energy expenditure - i.e. a certain amount of power.

---------------------------------1 watt-s = 1 joule. Also previously stated, a watt is instantaneous work. Add the time factor and it becomes an amount of energy.

300,000 joules = 300,000 watt-s, or 5000 watt-minutes, or 83 watt-hours.

If you were to provide 83 watts of power over the period of an hour, you'd be using the energy equivalent of 300,000 joules.

If you used a more useful period, say the acceleration time of a car going from 0-55 mph over 10 seconds, you'd have 50,000 watts over 10 seconds. That's 50,000 watts delivered for 10 seconds equaling the energy of 300,000 joules... ~65hp for 10 seconds. Reasonable for a 2000lb car.

It's all there. People haven't given you the specific answer to your numerical problem, but they've given you the tools to figure it out.

You are correct. This is incorrect. kj cannot equal w. Energy and power are different quantities. I suggest you brush up on some basic physics fundamentals and then it will become easier to correctly apply the math.another online conversion utility says that 300kj (rounded up from 292) = just 83w!!! there's no way that can be right

Regards,

major

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304 Posts

I mean no offense by this, but you seem to have a serious problem with units. It's either self-imposed, because you make assumptions, or you're not careful with your reading/comprehension.Using "engineering" units, convert mph to fps, multiplying by 22/15: 55 mph = 80 . Divide weight (in pounds) by 32.174 to get mass in slugs. Substitute these values in formula above; you should get 215.9 × 10³(10,000???!!!)ft lb.(215900???? formula calls for 215.9 x 1 to get 292.72 result!)Finally, convert to J, multiplying this by 1.356 J/ft lb. I get 292.72 kJ.

Let's look at what you found... 215.9 x 10³. First off, 10³ = 1000, not 10,000. So you end up with 215,900. Then the equation says, multiply by 1.356 J/ft to get Joules (note: not kilojoules). The result is 292760.4 joules, which is close to the stated 292.72 kJ. The cubing was fine.

See Major's post for the rest. But you're probably not reading this anyway...

trying to get the math down but that darn apples & oranges crap as well as bogus info even within a formula is holding me back. i have this INCORRECT kinetic energy formula to start with,

that's OK though, the 10 CUBED can just be ignored and just multiply 215.9 by 1.356 to get the proper 292.72 instead of 292720.Using "engineering" units, convert mph to fps, multiplying by 22/15: 55 mph = 80 . Divide weight (in pounds) by 32.174 to get mass in slugs. Substitute these values in formula above; you should get 215.9 × 10³(10,000???!!!)ft lb.(215900???? formula calls for 215.9 x 1 to get 292.72 result!)Finally, convert to J, multiplying this by 1.356 J/ft lb. I get 292.72 kJ.

215.9 x 1.356 = 292.7604kj actually. they didn't even multiply their own numbers correctly DESPITE the erroneous cubing.

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56 Posts

the formula was shoddy talking about kj one second then plain old joules the next.

why on earth should i have to study physics when all i want is a simple formula (or group thereof) that converts mass & velocity into watts? that's ALL i'm looking for eg. mass x velocity x .1234 = ergs, ergs divided by 4.321 = horsepower & horsepower x 9.876 = watts. that's all i'm trying to get to, but can't find the COMPLETE formulas. if KJ can't be converted to watts, then that's the wrong formula.

why does EVERYONE in this forum have to be so difficult?

and everyone joining in to attack me about reading needs to go back and read what i said. dimples lower drag by creating slippery turbulence. you can try to quibble with semantics and say that's not true when it is because i didn't put it in the words YOU WANT but too freakin' bad! that is exactly how it works! i learned that by FREAKIN' READING by the way.

just as all of the formulas etc. i find compare apples and oranges, so do you all compare mathematical dyslexia with illiteracy which have nothing to do with each other at all. i can deal with formulas that use up to basic algerbra, but not sine, cosine & tangents etc. as long as the formulas are systematically broken down one step at a time. when 10x formulas are listed at once though, it becomes an overwhelming blur to me and it becomes hard to ingest no matter how much i stare at it.

anyways... thanks for nothing everyone. it's become clear that no one is ever going to answer any question i say and everyone is simply here to pat themselves on the back because math comes easier to them than someone else who unfortunately struggles with it. thanks for all of your comments about how stupid i am. they really helped clear everything up.

so... the formula is:

people with name & number dyslexia shouldn't be allowed to drive electric no matter what their ACTUAL IQ is cars because they're too stupid. OK... got it. i tell you, i'd love to take an IQ drag race with everyone at the site that measures high IQs with a test that isn't time based and see how well you can visualize unseen sides of a cube & other real world type problems as well as SOME math because i scored a 157, dyslexia and all.

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304 Posts

I'm pretty sure I don't have to worry about the OP reading this and taking offense either, since not only have several people given the answers to his questions from a theoretical standpoint... and from a literal standpoint.

Duncan seems to be the only person he reads.

Maybe I'm in his "ignore" list and he's just not getting the posts. In which case, I suppose this post is just as pointless.

Why else would someone post

at 1:37 pm PST when at 10:16am PST I wrote,"if no one pointed it out yet, 10 cubed is 1,000 and not 10k as 10 to the first is 10."

It's also hard to point out the difference between a Joule and Kilojoule when the answer makes the OP feel stupid. But how much simpler can the explanation get? It was not my intention to make you feel stupid. It was my intention to point out that 1000 joules = 1kJ... and countless other relationships."Let's look at what you found... 215.9 x 10³. First off, 10³ = 1000, not 10,000."

OP... ARE YOU READING THIS?!?!

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7,793 Posts

We're not being difficult. Do you read the replies to your posts?why does EVERYONE in this forum have to be so difficult?

We have posted regarding this several times. I will put it as simple as I can. MASS times VELOCITY equals NOTHING !!!!!!!!!!! Meaning that the product of mass and velocity does not result in any useful quantity in any known system of physics or units in this universe, as far as I am aware.*why on earth should i have to study physics when all i want is a simple formula (or group thereof) that converts mass & velocity into watts? that's ALL i'm looking for eg. mass x velocity x .1234 = ergs, ergs divided by 4.321 = horsepower & horsepower x 9.876 = watts. that's all i'm trying to get to, but can't find the COMPLETE formulas. if KJ can't be converted to watts, then that's the wrong formula.

Furthermore, an erg = 100 nanojoules, which is a unit of energy. ENERGY is not POWER. So you can NOT convert units of energy to units of power.

No simple factor (number) can be used to make a KJ into a watt.

Got that?

major

* edit. Mass times velocity equals momentum. I missed that. Not a quantity used much in the EV study, but nevertheless, a useful quantity in this universe afterall.

This is by far the most bizarre (yet entertaining) thread I have EVER read on ANY forum period...

Yep... It's like watching someone try to fit a square peg in the round hole.This is by far the most bizarre (yet entertaining) thread I have EVER read on ANY forum period...

Hey Major,We're not being difficult. Do you read the replies to your posts?

We have posted regarding this several times. I will put it as simple as I can. MASS times VELOCITY equals NOTHING !!!!!!!!!!! Meaning that the product of mass and velocity does not result in any useful quantity in any known system of physics or units in this universe, as far as I am aware.

Furthermore, an erg = 100 nanojoules, which is a unit of energy. ENERGY is not POWER. So you can NOT convert units of energy to units of power.

No simple factor (number) can be used to make a KJ into a watt.

Got that?

major

I'm not trying to quibble here but Mass times velocity equals momentum.

As simply as possible:

Energy divided by time equals power.

It takes a great deal of power to deliver a lot of energy in a short amount of time. A funny car goes from zero to 300 mph in 4 seconds, but it requires about 7000 horsepower to do so.

On the other hand, a tiny solar cell could still deliver megajoules of energy, but it would take years. The solar cell puts out very little power, but the total amount of energy it could deliver is nearly unlimited if you don't care how long it takes.

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Good point. I stand corrected. Momentum. Not something I use much. I double checked several places before posting that and could not see where the unit of kg*m/s was listed anywhere. Also did not see N*s. Oh wellHey Major,

I'm not trying to quibble here but Mass times velocity equals momentum.

p = mv

But I do read replies to my posts

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56 Posts

i have no problems with admitting my limitations or ignorance on any issue. to do so only makes one look stupider under the light of scrutiny. i am not a know it all and never will be nor will anyone else.

the round peg in a square hole analogy is very appropriate for this thread. that's my entire point. everything that i try to combined into a grand "unified theory" of ergs only frustrates me further because of all of the gaps that make the equations i DO have useless.

i KNOW there are formulas that will allow me to convert watts into velocity for a given mass and am relying on those that know them to share them because no keyword search i've tried, and i have, will lead me to them.

i'd love to bridge the ergs to time void but don't know how. the way i see it, there should just be a simple bar graph that has watts on the X axis and velocity on the Y for a given mass. even if no one has ever thought to make that info so user friendly (AND THEY SHOULD!!!!!!!), there has to be formulas that produce said non-existent bar graph. that the information seems hidden & shrouded in mystery no matter how hard i TRY to find it is frustrating. no, i never read that obscure book you did and in fact, there are absolutely ZERO books on EV conversions in my library that would contain that info COMPLETELY.

back to the square peg & round hole analogy, i'd like to modify it to

regardless, i would NEVER condescend to anyone seeking knowledge i have about something that they don't and would simply try to find the simplest & most direct route to them understanding the issue in plain english. those that condescend are the most worthless sort of people short of liars & thieves or worse in my eyes. they deserve no respect and will never get it from me.

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7,793 Posts

My God. I think you have read a reply In that case maybe the following will help.the round peg in a square hole analogy is very appropriate for this thread.

Please read the EV Information section of this site. http://www.diyelectriccar.com/forums/showthread.php?t=669now if only i could find the formulas for moving that object at 55mph in relation to planet earth i'd use the word progress.

There, under this sub topic, you will find http://www.diyelectriccar.com/forums/showthread.php?t=15508

And in that you can read this:

1. The POWER requirements of your car at a particular speed is:

Power in Watts = ((Mass in kg) (9.8m/s²) (Velocity in m/s) (Rolling Resistance)) + ((0.6465) (Coefficient of Drag) (Area in m²) (Velocity^3))

The 9.8m/s is acceleration due to gravity, the 0.6465 is 0.5 times the density of air in kg/m^3. If you enter the required numbers it will give you your power consumption in watts.

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56 Posts

too bad i don't know either the Cd or rolling resistance of my design. i will take a look at it and see if it's possible to ignore those 2 varables and get results.

rough draft of my "cheap, light & efficient" design

http://i188.photobucket.com/albums/z157/zeroemission/electrobug.png

if serial hybrids didn't guzzle pretty much the same amount of gas as a standard ICE car, it would be possible to turn a design like that into an under 500 pound vehicle with a very low Cd profile.

i'm not looking for Nth degree accuracy, just a ballpark estimate to design around. the best i've been able to do is imagine a space in between motorcycle conversions and typical EV conversions, moreso motorcyles as my nylon skinned tube chassis concept is closer to them in weight and drag coefficient.

if one can get better performance than a typical EV conversion building from scratch, but for the same price or less, unless you're given a donor car, it makes more sense to build an "electric skateboard" from scratch to me. i'm not a fan of imitating the look of ICE either unless one gets EV vanity plates to advertise the fact.

If you want to get range with your design then figure out a way to put fenders on it (open wheels are very bad for air resistance), and find some narrow, smoother tires. Big knobbies are very bad for rolling resistance.

too bad i don't know either the Cd or rolling resistance of my design. i will take a look at it and see if it's possible to ignore those 2 varables and get results.

rough draft of my "cheap, light & efficient" design

http://i188.photobucket.com/albums/z157/zeroemission/electrobug.png

if serial hybrids didn't guzzle pretty much the same amount of gas as a standard ICE car, it would be possible to turn a design like that into an under 500 pound vehicle with a very low Cd profile.

i'm not looking for Nth degree accuracy, just a ballpark estimate to design around. the best i've been able to do is imagine a space in between motorcycle conversions and typical EV conversions, moreso motorcyles as my nylon skinned tube chassis concept is closer to them in weight and drag coefficient.

if one can get better performance than a typical EV conversion building from scratch, but for the same price or less, unless you're given a donor car, it makes more sense to build an "electric skateboard" from scratch to me. i'm not a fan of imitating the look of ICE either unless one gets EV vanity plates to advertise the fact.

As a ballpark: Open wheels and square profile front and back, which you have, will probably give you a drag coefficient in the range of 0.7.

For rolling resistance you'll just have to do some Googling and put in numbers that are in a reasonable range.

For the frontal area, you should include everything between the pavement and the highest part of the car.

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i think i'd go with even smaller wheels than that.

i had pictured creating aero wedges like grand prix cars use in front of the wheels with lighting & turn signals inside them, but putting them in front of the back wheel would interfere with getting in and out which would already be a challenge without the added intrusion. i have symmetry issues and wouldn't like the look of just wedges in front of the vehicle only. cars should be narrower in the front than the back. i can't stand the look of reverse trikes.

i also imagined a full fairing that stretches the length of the car with one or both sides swinging down to be stepped over, but that just adds weight & complexity as does a front fairing.

i know i could get lower weight, inertia, rolling resistance & Cd using narrower tires, but i want the ride to have some "cool factor" to it too. aesthetics are very important to me. a cool looking car will win people over more than an efficient one. besides looking cooler, ATV slicks would offer better cornering. more than drag racing, i'd like to be able to dust corvettes in slaloms pulling 2g. part of the vehicles intended use would be to haul DJ gear to gigs and a sportier looking design projects a better image. i dread the idea of showing up to gigs in hideous orange U-hauls.

i'm not looking to set records, just to get 55mph & 50 mile range and 30 mile range for hauling as simply as possible. i like the KISS principle. any high performance on top of that is icing on the cake.

also, to keep costs down, the batteries i planned for the ride were 7-8 x 12v @ 155aH (US Batteries US 12V XC) in a T formation with 3 wide forming the seat area with the other 4-5 forming a channel between my legs for a low center of gravity and close to 50:50 weight distribution if that were enough juice to get the magic 55/50 numbers. if necessary, i have allowed for the possibility of mounting a pair of batteries sideways behind the 3 wides. i planned on using those US batteries as all of their higher capacity models are too tall & would add to the Cd.

one EV conversion site suggested 6v & 8v batteries, but when you do the math, you pay more and weigh more for a given wattage.

i guestimated a total cost of maybe $4000. $1000 for batteries, $1000 for having the frame built, $400 or so for suspension salvage, $1000 for electronics & $600 for miscellaneous fabrication i don't have the tools to do myself. that's in the range of "doable" for me.

from what i've gathered researching motorcycle conversions, if they can get 55/50 out of 4 deep cycle batteries, so 7 or 8 of them should offer better range & performance in a minimalist design like the electrobuggy. if i ever wanted to go cross country, i'd slap whatever size generator i'd need for highway speeds on a trailer for a serial hybrid. it would have been cool if i could just yank the batteries and throw a 30 pound generator in back as i first intended with this thread. that would save a lot of weight if only the juice were sufficient. it looks like those claims of a 5hp @ 75mpg opel GT serial hybrid are pure lies.

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