[figgy]

Coasting under power

I've found that many automatic transmission cars have quite a lot of continous acceleration if left in drive.

The way be compare would be to make certain that the Corolla is in true neutral and that the engine is disengaged.

If the corolla is on a flat or slight incline and you put it from park to drive or neutral to drive, does that start it moving? Put it up in a garage, and I bet you will see it driving the wheels. Put the Insight up, and they won't move.

I have a friend with an Escort which accelerates all the time in drive, and I know the Jeep Waganeers used to have a lot of acceleration without any foot on the pedal. I don't know if they still do.

The problem can be made even worse if the car is not in the peak of service.

I bet that is what you are observing.

 

[Guest]

Hi Figgy:

___Yes, there is definitely Transmission creep in the Corolla but I didn’t think it would have an effect at high speeds? The next time I do a coast test, I will drop it into Neutral as you suggested. Great suggestion by the way! This will tell me if the transmission/engine was assisting in the coast tests. I am not complaining in the least as my last 95 mile commute in the Insight 2 days ago gave me an 87.4 mpg reading in sub 30 degree temperatures

___Good Luck

___Wayne R. Gerdes
___Hunt Club Farms Landscaping Ltd.
___[email:m5zxi034][email protected][/email:m5zxi034]

 

[cakley]

the auto trans should be a major factor.

Also the corolla has heavier tires/rims that would "store" alot of rotating energy.

 

[MikeF]

I would think that the lighter weight of the Insight is probably a factor as well. Although it's more streamlined than the Corolla, there is still friction from the wind, and the Insight has significantly less momentum (mass * velocity) than a Corolla at the same speed. I don't know whether the equation would be linear or not, but assuming it is....

Assuming that the sum of all drag on the Insight (rolling resistance, air resistance, friction in the bearings, compression braking, etc.) is defined as "drag," if the ratio of drag to weight in the Insight is higher than the ratio of drag to weight in the Corolla, wouldn't the Insight lose speed faster?

How's that for factless speculation?

MF

 

[Holicow]

Yes, this is interesting theoretical speculation. Good mind aerobics, anyway.

The difference in total air drag force would not be huge at those low speeds, and in fact would diminish greatly as speed slows (drag is proportional to the square of velocity).

More weight/mass equals more momentum, as has been mentioned several times, and this is probably a big factor, given the low speed/air drag involved.

And the auto tranny in drive will tend to add thrust below a given speed...

I have no idea what I am talking about....ow, my brain.... :roll:

 

[Guest]

Hi All:

___You had me thinking last night unfortunately … What I will do is get up to speed (55 mph) on a flat portion of Rt. 41 at night in both and see how far each will coast according to their respective odometers while in neutral. The Insight’s odometer and speedometer are slightly fast in reality but over a ½ mile distance, it shouldn’t be enough to skew the results.

___I believe the Integrity’s have higher RR then the Bridgestone’s at 50 #’s? I also believe the Insight’s wheel bearing frictional drag was possibly designed for low friction vs. the off-the-shelf HW as was the Corolla’s more then likely? The Cd and frontal area of the Insight make it a far more likely candidate to conserve its energy from a given speed to 0 mph I believe? The inertia of the Corolla’s wheel tire combo makes sense but I believe the momentum equations cancel out the mass so it shouldn’t have an effect in the inclined ramp scenario. It has been 20 years since my last Physics class

___Good luck and thanks to you all.

___Wayne R. Gerdes
___Hunt Club Farms Landscaping Ltd.
___[email:38lvlqjm][email protected][/email:38lvlqjm]

 

[figgy]

Momentum

I agree with everyone about the heavier car with heavier wheels/tires etc. having more momentum AND therefore maybe going further even if it has more drag and is less efficient on the road.

Most importantly, we must not forget that the big heavy auto thing will coast further than the tiny little car ONLY because more gas was used to get the big heavy auto thing up to speed in the first place!

You might coast further in the Corolla (Heavy Auto Thing, HAT), but if you want to be fair to the Insight (the TLC), you should let it also use while coasting all the gas the HAT used to get up to speed.

:roll:
Moral: TLC is better than HAT on GAS.

p.s. I think my brain is fried as well.

 

[Guest]

Hi Figgy:

___You almost had me fall off the chair :lol:

___I am dreading the Acronym you come up with for the 4,400 # MDX

___Good Luck

___Wayne R. Gerdes
___Hunt Club Farms Landscaping Ltd.
___[email:udfu2wz1][email protected][/email:udfu2wz1]

 

[Tim Maddux]

I believe the momentum equations cancel out the mass

They do not. F=ma tells you that a (in this case a rate of deceleration) is inversely proportional to the vehicle mass for a given force. If the forces involved are not linearly dependent on vehicle mass, then the mass does not cancel out.

Aerodynamic drag force (as discussed in another thread) is the product of drag coefficient, air density, frontal area, and velocity squared. It has no dependence on vehicle mass. So a heavier car will travel farther. This is analogous to heavier objects having a higher terminal fall velocity in air.

I'm not so sure about rolling resistance.

 

[Insightful Trekker]

<snip>

This is analogous to heavier objects having a higher terminal fall velocity in air.

I'm not so sure about rolling resistance.

I seem to remember Leonardo da Vinci disproving this a couple hundred years back by dropping two different mass spheres off the tower of Pizza (even before it was "leaning" <g>). If you roll two spheres of different mass at the same velocity the sphere of greater mass will roll proportionately farther. All elements of "friction" are the much smaller factor in the equation.

What has not been stated but we all know is the very not so hot aspect is that you prevent any regenerative braking energy recovery when "coasting."

 

[Guest]

Hi All:

___Here is my reasoning that mass cancels in the equation … All the Kinetic Energy of either car is transferred to Potential Energy when either car reaches 0 speed at the top of said Ramp. I am simplifying by leaving out all resistance effects although in actuality, the Insight should have less resistance imho?

KE=½ MV**2
PE=MgH

___If all the KE of either the Corolla or Insight were converted to PE, (0 speed at some given height above where the two automobiles stopped providing power/started coasting), that means the 2 equations must be equal.

KE = 1/2MV**2
PE = MgH

1/2M(Corolla)V(Corolla)**2 = M(Corolla)gH --> Masses cancel leaving --> 1/2V(Corolla)**2 = gH
1/2M(Insight)V(Insight)**2 = M(Insight)gH --> Masses cancel leaving --> 1/2V(Insight)**2 = gH

___Since the Velocity of the 2 automobiles (Corolla and Insight) are the same at To (55 mph) and Tf (0 mph), the height they would rise should be the same (~ 50 ft), and g is the gravitational constant, both should have transferred all of their KE to PE after the same amount of height increase. Afterwards, it’s a question of friction over the 1/3 – 1/2 mile of road, not the KE (Mass dependant) of each entering the ramp.

___Now go dust off those Physics books out and help me along with this

___Good Luck

___Wayne R. Gerdes
___Hunt Club Farms Landscaping Ltd.
___[email:2etaefl8][email protected][/email:2etaefl8]

 

[Yves M.]

HI,

Unless I have missed something, no tests where done with both cars in neutral. For sure the automatic left in drive will help moving forward.

I think that there is no need for mathematics until a test is done with a good case: both in neutral

No?

 

[Guest]

Hi Yves:

___You are entirely correct …

___Good Luck

___Wayne R. Gerdes
___Hunt Club Farms Landscaping Ltd.
___[email:29wfl37q][email protected][/email:29wfl37q]

 

[b1shmu63]

In a vacuum all objects fall at the same velocity. In air a steel ball falls faster than a feather. Terminal velocity occurs when the force of gravity matches the force due to aerodynamic drag.

 

[Holicow]

edit: oh, nevermind....

Well, I changed my mind again. That "assume" thing really is true, at least in my case.

Now, like you, I don't think mass may make a difference in distance up a grade since gravity would exert more force in a direction opposite.

ow....brain cramp.....ow ow ow...


I seem to recall doing this same problem way back when, in basic physics. This is one of those concepts that proves that intuition is not always right, and sometimes is completely wrong. Add all the variables and you got a mess....

 

[Tim Maddux]

I seem to remember Leonardo da Vinci disproving this a couple hundred years back by dropping two different mass spheres off the tower of Pizza

Galileo, according to popular lore, although he never wrote about actually performing the experiment, so scientific historians consider the story to be apocryphal. In any case, the supposed test was of the gravitational constant, and not of terminal velocity.

If you roll two spheres of different mass at the same velocity the sphere of greater mass will roll proportionately farther. All elements of "friction" are the much smaller factor in the equation.

Without friction, all spheres would roll forever. Wayne is right that "it's a question of friction over the 1/3 - 1/2 mile of road," which is neglected in his equations and which is (as I said before) independent of mass.