Can someone help me out explaining acceleration to a friend?

[jdoggg12]

He's trying to explain this in terms of a motorcycle...

<div class="FTQUOTE"><begin quote>1st. If you nail the throttle hard in 1st then knock it into nuetral (as someone said before) MOMENTUM will continue to allow you to accelerate to a point where you start to slow down again.

...and if youdon't believe me try it yourself. The only time you won't continue to acclerate is if you are holding a constant speed when you pull the clutchin.... or if you hit a wall.
</end quote></div>


I told him that as soon as the clutch is (dis)engaged, you will stop accelerating, regardless of how quickly you were accelerating prior to pulling the clutch in. HE believes momentum will keep him accelerating for a brief period before the bike starts to lose speed.



Anyone have an argument that will indisputably show him that he is wrong? A link with an explanation or something?

Thanks!


To clarify:

-This is assuming the bike is accelerating (hard) at the time the clutch is engaged

-Acceleration (in this example) is referring to the gain in speed (positive acceleration)

-Letting off the gas is not really the question - engaging the clutch is, as it is more immediate and not bound by what the motor would do

-The question is really this:
-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.

If you're under full acceleration on a sportbike (any gear) and you engage the clutch quickly, you will briefly(1-2 seconds) continue to accelerate then start to slow down.

I say he's dead wrong.

 

[Riverhound777]

He might keep accelerating if he is going downhill

 

[Zolty]

maybe there is a strong wind at his back.

 

[JulesMaximus]

Originally posted by: jdoggg12
He's trying to explain this in terms of a motorcycle...

<div class="FTQUOTE"><begin quote>1st. If you nail the throttle hard in 1st then knock it into nuetral (as someone said before) MOMENTUM will continue to allow you to accelerate to a point where you start to slow down again.

...and if youdon't believe me try it yourself. The only time you won't continue to acclerate is if you are holding a constant speed when you pull the clutchin.... or if you hit a wall.
</end quote></div>

I told him that as soon as the clutch is (dis)engaged, you will stop accelerating, regardless of how quickly you were accelerating prior to pulling the clutch in. HE believes momentum will keep him accelerating for a brief period before the bike starts to lose speed.

Anyone have an argument that will indisputably show him that he is wrong? A link with an explanation or something?

Thanks!

He's nuts. As soon as you remove the drive you will begin to slow down because of aerodynamic drag and rolling resistance from the weight of the bike + rider. Assuming you aren't riding downhill of course.

 

[pnad]

Not sure if this analogy is correct, but does a bullet stop accelerating as soon as it leaves the barrel? (I really don't know)

Above a certain speed it takes an appreciable amount of force to keep a vehicle moving against wind and friction. At lower speeds there may be enough kinetic energy to continue acceleration briefly before wind and friction begin to decelerate you.

 

[JulesMaximus]

Originally posted by: Zolty
maybe there is a strong wind at his back.

I wonder how much wind you'd need to accelerate a motorcycle & rider...150mph? 200mph? Either that or a large sail.

 

[silverpig]

The simplest way is:

F = ma

As soon as the clutch is engaged, there is no force, hence no acceleration.

 

[Safeway]

How old is your friend? I learned about this principle in 5th grade.

 

[silverpig]

Originally posted by: pnad
Not sure if this analogy is correct, but does a bullet stop accelerating as soon as it leaves the barrel? (I really don't know)

Above a certain speed it takes an appreciable amount of force to keep a vehicle moving against wind and friction. At lower speeds there may be enough kinetic energy to continue acceleration briefly before wind and friction begin to decelerate you.

The answer to the first question is:

Simple case, it stops accelerating. Realistically, it continues to accelerate (probably) as the high pressure gases rush out after the bullet. There is a higher pressure behind the bullet than in front so it still accelerates.

Kinetic energy doesn't accelerate you. Forces do. If there was no friction of any type and you cut the engine, he'd continue at the same speed forever, but he would not accelerate.

 

[jdoggg12]

Haha, well to clear it up a bit: We're assuming its on flat ground with minimal wind factoring in.


This:

Originally posted by: silverpig
The simplest way is:

F = ma

As soon as the clutch is engaged, there is no force, hence no acceleration.

...is what i'm looking for, but a longer explanation for the laymen. Its been years since i took physics and although i don't remember the technical aspects, i remember the concepts quite clearly.

And yes, the gun question doesnt really apply since the gasses exiting the gun dissipate and dont really have an immediate on/off effect (relatively).

 

[waggy]

Originally posted by: jdoggg12
Haha, well to clear it up a bit: We're assuming its on flat ground with minimal wind factoring in.


This:

<div class="FTQUOTE"><begin quote>Originally posted by: silverpig
The simplest way is:

F = ma

As soon as the clutch is engaged, there is no force, hence no acceleration.</end quote></div>

...is what i'm looking for, but a longer explanation for the laymen. Its been years since i took physics and although i don't remember the technical aspects, i remember the concepts quite clearly.

And yes, the gun question doesnt really apply since the gasses exiting the gun dissipate and dont really have an immediate on/off effect (relatively).

not going to get much more basic the F=ma

take away F (gas of the bike) then you can't have acceleration. Mass really does nto matter in this question.

 

[mugs]

<div class="FTQUOTE"><begin quote>Originally posted by: jdoggg12
Anyone have an argument that will indisputably show him that he is wrong? A link with an explanation or something?
</end quote></div>

Get in a car and do an experiment. Accelerate, watch speedometer, depress clutch, watch speedometer.

 

[FoBoT]

Originally posted by: silverpig
The simplest way is:

F = ma

:thumbsup:

 

[jdoggg12]

Thanks for your help guys!

 

[mooncancook]

Originally posted by: silverpig
The simplest way is:

F = ma

As soon as the clutch is engaged, there is no force, hence no acceleration.

I believe there's a friction force acting in the opposite direction, so you'll probably be decelerating, though at a rather small rate

 

[hanoverphist]

being a long time MC rider, i can guarantee you the bike definitely will stop accelerating when you pull the clutch in, no matter how fast youre going when you do it. my bike can hit 45 in 1st gear at 4k rpm, and if i just pull the clutch in ill coast, but not accelerate at all. once you remove the force of the engine, momentum will keep you going at the constant speed of the acceleration until friction takes over and slows you down. momentum cant push you faster, otherwise a pendulum would go higher than the start point, which is proven fact it wont. and the wind question. i would get pushed forward by gusts at stop lights that were just around 30mph, so i doubt youd need to have 150+mph winds to propel a rider. theres very little friction on those tires, since there isnt as much road contact as there is on a car or truck.

 

[JulesMaximus]

Originally posted by: hanoverphist
being a long time MC rider, i can guarantee you the bike definitely will stop accelerating when you pull the clutch in, no matter how fast youre going when you do it. my bike can hit 45 in 1st gear at 4k rpm, and if i just pull the clutch in ill coast, but not accelerate at all. once you remove the force of the engine, momentum will keep you going at the constant speed of the acceleration until friction takes over and slows you down. momentum cant push you faster, otherwise a pendulum would go higher than the start point, which is proven fact it wont. and the wind question. i would get pushed forward by gusts at stop lights that were just around 30mph, so i doubt youd need to have 150+mph winds to propel a rider. theres very little friction on those tires, since there isnt as much road contact as there is on a car or truck.

Depends on the bike/rider I guess.

 

[Jeff7]

I'd love to see a mathematical explanation for his reasoning as to how the car can continue to accelerate. Acceleration requires energy input. Once the gas pedal is let off, there is no further energy input, and thus no acceleration. A body's momentum will never accelerate it, but only serve to keep it in motion at a constant speed, assuming it is not acted on by anything else. In the car's case, the momentum helps to fight the friction which opposes the car's movement, but it most certainly will never cause the car's speed to increase.

 

[nakedfrog]

MOMENTUM will continue to allow you to accelerate to a point where you start to slow down again.

I just wanted to point out that this sentence makes my brain hurt.
It will allow you to accelerate... to a point where you start to slow down? So, he's discovered a way to make a motorcycle move at speeds faster than light?
Wait, what?

 

[Gunslinger08]

Technically, you'll still be accelerating.. negatively.

Or you could continue to accelerate positively for a short period of time, if your clutch blows.

 

[ch33zw1z]

Originally posted by: jdoggg12
He's trying to explain this in terms of a motorcycle...

<div class="FTQUOTE"><begin quote>1st. If you nail the throttle hard in 1st then knock it into nuetral (as someone said before) MOMENTUM will continue to allow you to accelerate to a point where you start to slow down again.

...and if youdon't believe me try it yourself. The only time you won't continue to acclerate is if you are holding a constant speed when you pull the clutchin.... or if you hit a wall.
</end quote></div>


I told him that as soon as the clutch is (dis)engaged, you will stop accelerating, regardless of how quickly you were accelerating prior to pulling the clutch in. HE believes momentum will keep him accelerating for a brief period before the bike starts to lose speed.



Anyone have an argument that will indisputably show him that he is wrong? A link with an explanation or something?

Thanks!

maybe his clutch/tranny are worn out from him doing this constantly, would explain why it takes a few seconds for him to stop accelerating.

 

[RGUN]

I would like someone to explain what impulse is occuring that stops the acceleration. If you are accelerating and let off the gas, you still have the force of the acceleration behind you, you cant be accelerating at 10 m/s^2, let off the gas and all the sudden be at 0 m/s^2... there is a time during which you are still accelerating albeit in a continuously declining amount until the time at which you reach 0 (and begin to decelerate).

 

[So]

Originally posted by: RGUN
I would like someone to explain what impulse is occuring that stops the acceleration. If you are accelerating and let off the gas, you still have the force of the acceleration behind you, you cant be accelerating at 10 m/s^2, let off the gas and all the sudden be at 0 m/s^2... there is a time during which you are still accelerating albeit in a continuously declining amount until the time at which you reach 0 (and begin to decelerate).

Wow.

Just...

...wow.

 

[waggy]

Originally posted by: RGUN
I would like someone to explain what impulse is occuring that stops the acceleration. If you are accelerating and let off the gas, you still have the force of the acceleration behind you, you cant be accelerating at 10 m/s^2, let off the gas and all the sudden be at 0 m/s^2... there is a time during which you are still accelerating albeit in a continuously declining amount until the time at which you reach 0 (and begin to decelerate).

if you let off the gas what is the force? thats kind of important.

oh and what you are talking about is not acceleration..

 

[jjzelinski]

You know its possible your friend is being mislead by a misunderstanding of mechanics. He's probably thinking that if you're accelerating rapidly and you're giving allot of gas that it feels like you continue to accelerate when when you release the gas. This would be because you're still combusting the extra volume of fuel that was delivered directly prior to the release of the gas pedal. Doesn't work like that when you work the clutch though since the engine is immediately uncoupled from the drivetrain so the excess fuel "burn off" is not transmitted to the wheels. As was already mentioned, as soon as you work the clutch you immediately start to decelerate.

I'm sure by my shoddy terminology it's clear I'm a layman at best but that's my theory and I'm sticking to it