Is Future uncertain

[Guest]

As soon as you lift of the throttle everything starts decelerating, including the wheels. To push (as is your claim), the un-driven wheel would need to accelerate. The total force would need to be forwards, but it isn't, the net force is to drag the car backwards. 

So assuming my car has a mass of 1800kg at 60mph that gives us a momentum of 48240 kg m/s - still not enough to "push" the car when you lift off the throttle.

A 5kg wheel tyre will have a fwd momentum of about 134 kg m/s - you see the problem?

If you wouldn't mind working out the rotation forces for us? Too hard for me and you've already said you understand physics better than everyone here, we are just lay people after all.

I think this is the formula you need, but feel free to correct me.

 

KE (rolling) = 1/2 mv²_cm + 1/2 I _cm w²

 

[darrude]

Comdien, did you spend a year or 2 reading this book as well:

 

 

 

 

[Guest]

9 minutes ago, darrude said:

Comdien, did you spend a year or 2 reading this book as well

 

 

 

 

Something similar. Although I am wondering if the true knowledge lies with youtubers explaining how physics can be used to prove the flat earth? 😂

[noby76]

1 hour ago, Comedian said:

As soon as you lift of the throttle everything starts decelerating, including the wheels. To push (as is your claim), the un-driven wheel would need to accelerate. The total force would need to be forwards, but it isn't, the net force is to drag the car backwards. 

So assuming my car has a mass of 1800kg at 60mph that gives us a momentum of 48240 kg m/s - still not enough to "push" the car when you lift off the throttle.

A 5kg wheel tyre will have a fwd momentum of about 134 kg m/s - you see the problem?

If you wouldn't mind working out the rotation forces for us? Too hard for me and you've already said you understand physics better than everyone here, we are just lay people after all.

I think this is the formula you need, but feel free to correct me.

 

KE (rolling) = 1/2 mv²_cm + 1/2 I _cm w²

 

Get us a lab, 4 independent electronic wheel rollers which has the capability to spin and apply brakes on each wheels independently. 

your quote above "As soon as you lift of the throttle everything starts decelerating," so are you saying during this deceleration or energy depleting  process the rear tyres on a FWD car is stagnant?

if yes explain why?

if no, answer what the rear wheel tryes are doing to the rear end of a FWD car or the rear end of your 1800KG weight car during the deceleration process when no throttle is being applied.  

 

[Guest]

🤣🤣 get us a lab - listen to yourself, man.

Answer no - I think - you're question is flawed.

The momentum energy of the wheels is probably lost in a fraction of approximately 100/s of a second and is not enough to Push the car. The argument is not about what energy exists it is about if it is enough to effect a push on the car.

You can exert a force on the Empire state building by pushing it with your hands. But no-one sat on floor 42 is going to say "can you feel that?"

Do you know what a thought experiment is? Imagine rolling a wheel off the back of a flat bed truck (but let's put the bed of the truck 1mm off the ground to avoid bounce.) Truck is stationary so as the wheel hits the floor it will carry on rolling in the direction of travel. Now roll it off the back of a 60mph truck. What happens?

[darrude]

Noby, I'm confused by either why you aren't understanding what the majority are saying, or maybe we are confused by what you are quoting.

Correct me if I'm wrong as there has been lots of talk about weight transfer / squatting spinning cars on ramps and dropping them etc (and I can't be bothered re-reading the thread)...  But are you saying that the interia of the spinning rear wheels (on a front wheel drive car) is sufficient to drive the vehicle forwards.  

As I like a bit of hyperbole:

Yes, theoretically this is possible.  Lets say the car is a front wheel drive robin reliant.  The middle of the road is good and clear and the outside of the road (for the rear wheels is on perfectly smooth ice).  The car brakes from 100mph to 5mph, as the rear wheels are on ice they slow down much slower, just as the rear wheels happen to hit a clear patch of shell sure grip tarmac the drivers takes his foot of the brake, then yes, theoretically there will be a very minor insignificant push from the rear wheels, as spinning wheel kinetic energy is dispersed.

Had the wheels had grip then as soon as the brake was released the car would continue to roll forward at 5mph, the engery from the wheels already having turned to brake heat / noise etc.

 

[noby76]

7 minutes ago, Comedian said:

You can exert a force on the Empire state building by pushing it with your hands. But no-one sat on floor 42 is going to say "can you feel that?"

 

so the argument went from does FWD cars squat i said yes he said no others confirmed they do.    noby 1   , comedian 0

then went to does rear wheels carry momentum to assit in pushing the rear end of a FWD others confirmed yes it does carry some momentum energy when in motion. noby 1 comedian 0

 

and quote above has now switched to if that energy can be felt or not.  who is moving the goal post now eii??

fact that you might not feel that energy in the  FWD does not mean its not there..

[darrude]

regarding squatting, it has nothing to do with fwd/rwd/awd:

It is about the transmission of force (both in acceleration and braking) being at that point where the wheels touch the ground, whereas this force has to overcome the inertia of the vehicle that is focused at the centre of gravity.

Since the transmission of force is below the centre of gravity, you then develop a rotational force caused by forces at one point acting opposite to forces at another point (effectively, it is as if you had a lever running from the ground upward, and you were pushing one end of the lever in the opposite direction to the other end of the lever, so the lever rotates).

[J Henderson]

[darrude]

with regards rear wheels carrying momentum, then in real world scenario's then no more than the spare wheel in the boot (if only we had one eh!)

 

[noby76]

5 minutes ago, darrude said:

regarding squatting, it has nothing to do with fwd/rwd/awd:

 

so as you can see, the whole praise on RWD cars only having that sqautting charcteristics only is false. above confirms all will indeed squat irrespective of drive layout

anyway thanks for your time guys its been fun..😎

 

[rich1068]

So should I use winter tyres or not?

[darrude]

I am going to generalise here, what I am going to say is generally, but not always true

RWD Advantages:

Vehicle architecture allows 50/50 weight distribution, with engine mass within the axles.

Engine can sit lower in vehicle reducing centre of mass.

Better work load split, front wheels steer, rear wheels drive.

Weight transfer during acceleration pushes wheels into ground, increasing friction.

Disadvantages, 

Driven wheels push car straight during cornering (oversteer)

Increased cost and weight

increased package on constraints.

 

FWD advantages:

Reduced Cost and packaging.

Reduced overall weight.

Acceleration during cornering is in the direction you want to travel (assuming you don't get understeer).

 

Disadvanatages:

Poor weight distribution due to engine sitting on top of front axle to avoid need for a drive shaft (although this is why FWD is better in snow).

torque steer.

Drive train elements affect steering 'feel'.

Lift off wheel spin, especially on FWD car's with relatively good weight distribution.

generally a higher centre of mass from the engine.

 

The Key however is equal and even weight distribution.  Equal weighting balances the work load during corning, makes the car more stable during braking.  

have a look at engineering explained on you tube, he has a good way of explaining things.

[Guest]

If only that was his original point.

 

 

[darrude]

Just now, rich1068 said:

So should I use winter tyres or not?

only on the non driven wheels, let the free spinning momentum take you up the hills..  To be fair this is a perfect example of why you don't get the secondary push.

[rich1068]

Great stuff. Thank you. At last, someone who knows what they're talking about.

[Linas.P]

On 6/18/2018 at 10:33 AM, Comedian said:

The argument is not about what energy exists it is about if it is enough to effect a push on the car.

And even then only during deceleration/braking. The initial argument was that rear wheels will push FWD car during acceleration and not braking.

I think this nailed it:

On 6/18/2018 at 9:22 AM, Comedian said:

Something similar. Although I am wondering if the true knowledge lies with youtubers explaining how physics can be used to prove the flat earth? 😂

If we live on "flat earth" then there is potential for FWD cars "pushing" by the invisible force in rear wheels.

@noby76 - that is exactly sorts of idea we discussing here. Imagine explaining for somebody with basic education that "earth is flat" and imagine their face. That is most of our faces when you say that FWD car pushes with rear wheels... it is equivalent to conspiracy theory (and pretty dumb one for that) - do you understand ?

[Linas.P]

On 6/18/2018 at 9:49 AM, noby76 said:

Get us a lab, 4 independent electronic wheel rollers which has the capability to spin and apply brakes on each wheels independently. 

your quote above "As soon as you lift of the throttle everything starts decelerating," so are you saying during this deceleration or energy depleting  process the rear tyres on a FWD car is stagnant?

if yes explain why?

if no, answer what the rear wheel tryes are doing to the rear end of a FWD car or the rear end of your 1800KG weight car during the deceleration process when no throttle is being applied.  

I know it is waste of my time, but because I am that sort of the guy who likes arguing for the sake of it (and clearly has too much time to spare).. here we go:

1. before hiring the lab we need to identify and fix issues in your methodology, because otherwise we will get flawed results (due to the flawed methodology). lets see where you gone wrong with your proposed methodology first and why it doesn't make sense:

• 4 independent rollers are ok, but they should not be electronic or in any way driven or powered, can have brakes for practical reasons (maybe fail safe) - fine. Rollers represents the road surface and the roads are not powered right? We want to recreate realistic conditions and to have possibility to measure it. If rollers are powered, then they does not act as a road - they represent drive train, hence if you power only front rollers it is FWD, only rear rollers on RWD and all rollers on AWD. Because we are not trying to convert FWD car to AWD or RWD, we not going to power the rollers 
• you don't compare it against anything, hence you cannot conclude anything from that, you need "base line" measure, hence we will introduce identical car for comparison.
• vehicle has to power wheels by it's own engine power, that is because that is how it works in reality. Roads doesn't power our vehicles, engines and drive trains does. Rollers doesn't have suspension, hence cannot squat etc. hence is why rollers cannot power the wheels. Right?
• Finally, we not going to do braking test as that is completely different from acceleration and we will need different methodology to test it (if you interested we can go troughs that as well). Your claim was - rear wheels assists car during acceleration in pushing motion, so that is only thing we testing. OK?

2. lets create realistic testing steps for our imaginable test:

• lab with 2 sets of 4 independent rollers measured by sensors (with brakes.. just because).
• we have 2 sets of rollers and 2 identical FWD vehicles on both
• we strap both vehicle on the rollers, applying realistic tension equivalent to vehicle weight and average road surface grip - so that wheels can loose traction if if torque gets greater then grip.
• for baseline we will use 1st vehicle as it is, 2nd one will have solid concrete non-rotating stands, solid on the rollers - not rotating at all.
• we power both vehicle and accelerate from stand still to predetermined speed or to the maximum speed.
• we measure the torque generated in the rollers to determine whenever rear wheels assist acceleration in any shape or form or not.

3. the results (my guess):

• we start accelerating, both vehicles squats a little bit and we get little bit of skipping on the rollers as torque is greater then grip and weight transfer to the rear reducing grip further.
• front set of rollers starts spinning on both cars
• rear set of rollers just stays as they are, 1st vehicle because there are no power delivered to them, 2nd because rear wheels are solid concrete stands
• we measure the torque generated and it is same in both cases: 100% in front wheels, 0% in rears.

= conclusion, rear wheels does not assist in front wheel drive car acceleration.

> to further improve our baseline we can add and remove many variables e.g.

x. we can further prove the point, by mechanically connecting front rollers to the rear rollers on 1st vehicle. The vehicle will generate same torque to the front wheels, but will accelerate slower due to now having to push not only mass of drive train, front wheels, front rollers, but as well connecting shaft, rear rollers and rear wheels. So if anything - rear wheels are just dead weight which require energy to power. They do not assist acceleration at all, but resist acceleration - equivalent to their mass. (we almost created AWD contraption here + 4 rollers, except on AWD we would accelerate quicker as added weight would have been counterbalance by added grip).

y. we can now replace rear wheels with very heavy solid lead disks, running same test we will find that FWD car will generate same torque, but will accelerate slower, because heavier wheels will have more weight to resist acceleration. That only proves rear wheel acts as a dead mass and only in fashion of resisting the acceleration, not aiding it in any way.

z. we can replace rear suspension, to take it from equation to see if rear suspension has any role. We replace rear springs and any moving parts for solid concrete stands. Basically we bolt rear towers to concrete stands. This does not allow car to squat or move at all. Result more likely to be less skip on front rollers, because solid concrete minimises weight transfer from front to rear and car will accelerate quicker. Meaning that squatting and weight transfer actually doesn't help acceleration, quite opposite it reduces grip in front.

Now when you have decent methodology to start with and reasonable baseline to compare it with, you can certainly go and prove or disprove it in the lab. Or we can imagine one:

 

[darrude]

this thread....

[Linas.P]

9 minutes ago, darrude said:

this thread....

Except that book might be relevant to somebody... this thread isn't (except of realms of flat earth if that is your thing).

edit: I mean it was at first, but then stopped being so when we started discussing what kind of dark matter from parallel universe power rear wheels on FWD cars.

[noby76]

1 hour ago, Linas.P said:

 

Now when you have decent methodology to start with and reasonable baseline to compare it with, you can certainly go and prove or disprove it in the lab. Or we can imagine one:

 

 

give me a call once you have all the requirements i asked ready and proof will certainly be in the pudding. 

funny how guys still want to disagree even when it has been confirmed fwd cars squat and rear wheels in fwd car carry momentum whilst in motion.. 

[Linas.P]

Just now, noby76 said:

give me a call once you have all the requirements i asked ready and proof will certainly be in the pudding.

You asked? Then it is no point, because what you asked is to convert FWD to AWD to prove rear wheels assist in acceleration. I don't need lab for that - I already know that AWD uses are 4 wheels to accelerate.

[noby76]

Linas.. zip zip zip it. it has been confirmed not by me but by others on here give it up and take a chill pill.. once again FWD squat and FWD rear wheels carry momentum when in motion ohh poor Linas/comedian seems they all butt hurt  😭😂 .. you need a Kit Kat seriously..

[Linas.P]

First of all that's is not what you have said - you said rear wheels aid in acceleration and that is arguably quite different from caring momentum in motion.

Secondly even if that is true, why should I be butt hurt about it, neither I drive FWD, nor planning to have one - so it is kind of irrelevant for me.

Lastly, it probably wouldn't be too much to ask you where it was "confirmed" and by whom. 

[noby76]

go and play somewhere else  Linas i dont feel like playing with you today I am busy.. 😫