Can someone help me out explaining acceleration to a friend?

[waggy]

<div class="FTQUOTE"><begin quote>Originally posted by: RGUN
<div class="FTQUOTE"><begin quote>Originally posted by: waggy
<div class="FTQUOTE"><begin quote>Originally posted by: RGUN
<div class="FTQUOTE"><begin quote>Originally posted by: waggy
<div class="FTQUOTE"><begin quote>Originally posted by: waggy
<div class="FTQUOTE"><begin quote>Originally posted by: RGUN
You guys are really being a pain.... so at what exact instant are you telling me that you go from accelerating at whatever rate to not accelerating at all... do you realize how much force that would take and that during that time you would probably be subjected to many times the force of gravity?</end quote></div>

i want to be 100% sure on what you are saying.

so saying you are accelerting to 100mph. at 100 acceleration stops. since accelration stops you stop at zero mPH?

</end quote></div>


hey rgun can you please clerify this? is this what you are saying?


</end quote></div>


Im sorry, I dont understand the part Ive bolded
</end quote></div>

are you saying since the acceleration (force) of the motorcycle is zero the MPH the motorcycle is going goes to zero in the same instant? wich is not possible anyway.</end quote></div>

No, you will start to decelerate until the point at which you have 0 velocity.

</end quote></div>

yeap. we all agree on that no force no acceleration. no acceleration eventually you will have ZERO velocity.

but in no way shape or form will you have a postive acceleration without force.

 

[SSSnail]

Maybe his bike is hooked up with the NOS and has a really large after market exhaust can out the back, after he let off the throttle, the NOS continues to burn and the rocket-like propulsion of the exit gas through the exhaust will continue the acceleration. NOS, not just for fast cars anymore you know.

EDIT: Oh btw, I just like you guys to know the plane DOESN'T fly. Have at it.

 

[GasX]

What RGUN can't get past is the fact that F does not drop to zero instantly. He is fixated on the fact that the amount of force transmitted through the clutch drops as the pressure on the plates is reduced - Even though the slope of the curve is as close to vertical as you can imagine and that it hits zero when the clutch plates disengage.

Everyone else here is taking the eminently practical stance that squeezing the clutch is an instaneous reduction of the ability of the engine to transmit force to the wheels to zero.

10 points to RGUN for technical knowledge
0 points for communication skills
0 points for an ability to comprehend the practical side of his craft

 

[Howard]

Originally posted by: RGUN

I suspect you havent taken physics, Im a B. Eng with a specialization in solid mechanics.... This is my area of knowledge

Then why don't you know what jerk is?

 

[jdoggg12]

updated OP

For all intents and purposes, a clutch and be pulled-in in .25 seconds, so the time it takes to do is negligable on the resulting acceleration. Lets just assuming the time it takes to pull the clutch is instant b/c thats how it was intended to be perceived in the original argument.

 

[SVT Cobra]

Someone who isn't tired as hell interperate these graphs for me, I am too tired and starting to think i might be wrong.

 

[RGUN]

Originally posted by: Howard
<div class="FTQUOTE"><begin quote>Originally posted by: RGUN

I suspect you havent taken physics, Im a B. Eng with a specialization in solid mechanics.... This is my area of knowledge</end quote></div>
Then why don't you know what jerk is?

What has made you believe that I dont?

 

[waggy]

Originally posted by: SVT Cobra
Someone who isn't tired as hell interperate these graphs for me, I am too tired and starting to think i might be wrong.

that is the ugliest thing i have seen.

 

[SVT Cobra]

Originally posted by: waggy
<div class="FTQUOTE"><begin quote>Originally posted by: SVT Cobra
Someone who isn't tired as hell interperate these graphs for me, I am too tired and starting to think i might be wrong.
</end quote></div>

that is the ugliest thing i have seen.

I understand what KDun is trying to say now I think. Impulse is force over a time, and the force does not drop to zero instantly......

Now completely forgetting physics, which does not always work the classroom way in the real world and not the perfect frictionless consice time world.



.......The energy is still being transferred to the drive train and momentum is increase in sprung and unsprung weight, which would cause you to continue to accelerate for a slight bit before decelerating, and in a motorcycle the mass is very small so the OP's friend would notice it more than someone on a car.

Shit this is what I thought to begin with but then I went the physics route...maybe I am still wrong, I need sleep then I'll think this over.

 

[pray4mojo]

I dont even know whats being argued in this thread but all you guys need to do is chill out and draw a FBD.

/thread

 

[Cattlegod]

technically, your friend is right.

when you engage the clutch, you build up a little potential energy in the drive train (it twists and once it stops twisting, it begins turning the wheels). So if you are going balls to the wall and let off of the clutch, you will keep accelerating until the sprung energy is expended out of the rest of your powertrain. While it isn't a large effect, it does have a little one.

 

[SVT Cobra]

Yup your friend is right, I keep thinking about it in terms of calculus and practical and it works, you just need to remember even though the rate of change of acceleration is decreasing, acceleration can still be positive.

And, you can ignore those graphs as they don't mean a thing as we do not know the velocity of the bike/car.

Also I must note that this is noticeable but very small, but you friend also might be getting an amplified example ignoring his mass, because when you suddenly push in the clutch after pushing it to the red line their is a jolt as the wheels are suddenly not being powered, but after that jolt it may seem like it is going faster, when it fact it is only relative to the jolt.

 

[DivideBYZero]

Whatever happens, he's saving gas.

 

[waggy]

Originally posted by: Cattlegod
technically, your friend is right.

when you engage the clutch, you build up a little potential energy in the drive train (it twists and once it stops twisting, it begins turning the wheels). So if you are going balls to the wall and let off of the clutch, you will keep accelerating until the sprung energy is expended out of the rest of your powertrain. While it isn't a large effect, it does have a little one.

it wouldnt be noticable or traceable though. while not instant (not anything really is) its so fast i really doubt he is noticing.

 

[Cattlegod]

Originally posted by: waggy
<div class="FTQUOTE"><begin quote>Originally posted by: Cattlegod
technically, your friend is right.

when you engage the clutch, you build up a little potential energy in the drive train (it twists and once it stops twisting, it begins turning the wheels). So if you are going balls to the wall and let off of the clutch, you will keep accelerating until the sprung energy is expended out of the rest of your powertrain. While it isn't a large effect, it does have a little one.</end quote></div>

it wouldnt be noticable or traceable though. while not instant (not anything really is) its so fast i really doubt he is noticing.

There is plenty enough to be noticeable. I'm sure you are familiar with torque steer in front wheel drive cars. This is a direct result of this principle because you have varying length half shafts in the front that store different amounts of energy. If you are in a rear wheel drive car and depress and press the clutch it will lunge the car forward from the built up energy in the driveshaft.

 

[SVT Cobra]

Originally posted by: Cattlegod
<div class="FTQUOTE"><begin quote>Originally posted by: waggy
<div class="FTQUOTE"><begin quote>Originally posted by: Cattlegod
technically, your friend is right.

when you engage the clutch, you build up a little potential energy in the drive train (it twists and once it stops twisting, it begins turning the wheels). So if you are going balls to the wall and let off of the clutch, you will keep accelerating until the sprung energy is expended out of the rest of your powertrain. While it isn't a large effect, it does have a little one.</end quote></div>

it wouldnt be noticable or traceable though. while not instant (not anything really is) its so fast i really doubt he is noticing.

</end quote></div>

There is plenty enough to be noticeable. I'm sure you are familiar with torque steer in front wheel drive cars. This is a direct result of this principle because you have varying length half shafts in the front that store different amounts of energy. If you are in a rear wheel drive car and depress and press the clutch it will lunge the car forward from the built up energy in the driveshaft.

Unfortunately your analogy while sound and explains what you are saying that energy is stored, does not apply as you are still accelerating in both situations.

 

[nakedfrog]

Originally posted by: DivideBYZero
Whatever happens, he's saving gas.

Undoubtedly. It's always better to coast in neutral, regardless of whether or not you keep accelerating.

 

[RGUN]

Originally posted by: SVT Cobra
Yup your friend is right, I keep thinking about it in terms of calculus and practical and it works, you just need to remember even though the rate of change of acceleration is decreasing, acceleration can still be positive.

And, you can ignore those graphs as they don't mean a thing as we do not know the velocity of the bike/car.

Also I must note that this is noticeable but very small, but you friend also might be getting an amplified example ignoring his mass, because when you suddenly push in the clutch after pushing it to the red line their is a jolt as the wheels are suddenly not being powered, but after that jolt it may seem like it is going faster, when it fact it is only relative to the jolt.

Well Im happy you changed your mind even though you were so quick to dismiss me. I suppose it comes with the territory of ATOT, any time you disagree with someone its reduced to personal insults.

 

[Zenmervolt]

Originally posted by: Mwilding
What RGUN can't get past is the fact that F does not drop to zero instantly. He is fixated on the fact that the amount of force transmitted through the clutch drops as the pressure on the plates is reduced - Even though the slope of the curve is as close to vertical as you can imagine and that it hits zero when the clutch plates disengage.

Everyone else here is taking the eminently practical stance that squeezing the clutch is an instaneous reduction of the ability of the engine to transmit force to the wheels to zero.

10 points to RGUN for technical knowledge
0 points for communication skills
0 points for an ability to comprehend the practical side of his craft

Well of course the force is removed gradually, that's why nearly everone has specified that acceleration stops when the force of the engine is zero. (Not aimed at you Mwilding, aimed at RGUN.)

And yes, I realise that technically acceleration ceases when F(engine)=F(friction) and that once F(engine)<F(friction) negative acceleration begins even if F(engine) has not yet reached zero, but that's just getting too nit-picky.

ZV

 

[SVT Cobra]

Originally posted by: RGUN
<div class="FTQUOTE"><begin quote>Originally posted by: SVT Cobra
Yup your friend is right, I keep thinking about it in terms of calculus and practical and it works, you just need to remember even though the rate of change of acceleration is decreasing, acceleration can still be positive.

And, you can ignore those graphs as they don't mean a thing as we do not know the velocity of the bike/car.

Also I must note that this is noticeable but very small, but you friend also might be getting an amplified example ignoring his mass, because when you suddenly push in the clutch after pushing it to the red line their is a jolt as the wheels are suddenly not being powered, but after that jolt it may seem like it is going faster, when it fact it is only relative to the jolt.</end quote></div>


Well Im happy you changed your mind even though you were so quick to dismiss me. I suppose it comes with the territory of ATOT, any time you disagree with someone its reduced to personal insults.

The problem was I (and most others) were thinking the force on the wheels instantly goes to zero when the engine can no longer turn the drive shaft.


Actually now that I think about it again I say I am wrong because once the drive shaft is no longer turned by the engine, it is no longer moving any quicker, thus the car will never travel faster than the time you let off the gas, ignoring drive train loss and gain (which could store energy). We both are thinking in terms da/dt decreasing, but still being positive, unfortunately, once the gas is no longer driving the car, assuming everything is instant, and saying that momentum does not keep the car accelerating (which is not possible in a world with friction), there is no longer a force, therefor no acceleration, and the car can only slow down from there.

I assume your friend's sensation of continuing to be faster is actually the clutch popping, not actually acceleration.


So once again I say your friend is wrong.


Man I have more waffles than John Kerry, and thus a house of pancakes also.

 

[waggy]

Originally posted by: nakedfrog
<div class="FTQUOTE"><begin quote>Originally posted by: DivideBYZero
Whatever happens, he's saving gas.</end quote></div>

Undoubtedly. It's always better to coast in neutral, regardless of whether or not you keep accelerating.

hmm but its not safer. in fact coasting on a motorcycle is a bad idea.

 

[Vic]

The OP's friend is right. I think everyone arguing here forgot about the potential energy stored in the rotating mass of the drivetrain. There is a reduction in acceleration once the clutch is depressed, and that stored energy is relatively small and will be depleted within about a second, but you can accelerate smoothly through a shift if you do it properly. You can increase this effect (by increasing the potential energy) by engaging the clutch a split-second before you come off the gas, which results in that desired high note upon shifting.

 

[Zenmervolt]

Originally posted by: Cattlegod
There is plenty enough to be noticeable. I'm sure you are familiar with torque steer in front wheel drive cars. This is a direct result of this principle because you have varying length half shafts in the front that store different amounts of energy. If you are in a rear wheel drive car and depress and press the clutch it will lunge the car forward from the built up energy in the driveshaft.

Actually, torque steer is due to rotational torque caused by the kingpin axis not being in the same place as the center of the tire's contact patch. The gyroscopic effect of the spinning tire places a rotational torque on the steering axis. Normally the two torques cancel each other (straight line, full grip), but if one tire begins to lose traction or otherwise spins faster, the torques no longer balance and the effect is a "pull" on the steering.

While it's true that there is some small contribution to torque steer from unequal-length halfshafts, the vast majority of the effect is caused by the gyroscopic effects of the wheels and variances in their rotational speeds. This is why a limited slip differential will significantly reduce torque steer in a FWD car.

ZV

 

[jdoggg12]

Originally posted by: Vic
The OP's friend is right. I think everyone arguing here forgot about the potential energy stored in the rotating mass of the drivetrain. There is a reduction in acceleration once the clutch is depressed, and that stored energy is relatively small and will be depleted within about a second, but you can accelerate smoothly through a shift if you do it properly. You can increase this effect (by increasing the potential energy) by engaging the clutch a split-second before you come off the gas, which results in that desired high note upon shifting.

You're saying that the energy 'stored' in the drivetrain is going going to be exerted as acceleration? This is wrong. Even if there IS that energy, then it will be exerted on the disengaged clutch plate clutch plate (now spinning freely b/c its not being 'bogged down' by the motor) since it will offer less resistance than it would take to keep accelerating the bike.

 

[Cattlegod]

Originally posted by: SVT Cobra
<div class="FTQUOTE"><begin quote>Originally posted by: Cattlegod
<div class="FTQUOTE"><begin quote>Originally posted by: waggy
<div class="FTQUOTE"><begin quote>Originally posted by: Cattlegod
technically, your friend is right.

when you engage the clutch, you build up a little potential energy in the drive train (it twists and once it stops twisting, it begins turning the wheels). So if you are going balls to the wall and let off of the clutch, you will keep accelerating until the sprung energy is expended out of the rest of your powertrain. While it isn't a large effect, it does have a little one.</end quote></div>

it wouldnt be noticable or traceable though. while not instant (not anything really is) its so fast i really doubt he is noticing.

</end quote></div>

There is plenty enough to be noticeable. I'm sure you are familiar with torque steer in front wheel drive cars. This is a direct result of this principle because you have varying length half shafts in the front that store different amounts of energy. If you are in a rear wheel drive car and depress and press the clutch it will lunge the car forward from the built up energy in the driveshaft.</end quote></div>

Unfortunately your analogy while sound and explains what you are saying that energy is stored, does not apply as you are still accelerating in both situations.

I think the OP's situation is during an accelerative state. The OP's friend said that it won't continue to accelerate only if you aren't accelerating, which I also agree with. I don' think I'm misunderstanding what the OP is saying, but I might be with all of the damned extra html code put in there