Acceleration of a car and jet plane problem

[vysqn]

As we know, POWER is what accelerate a car, FORCE itself doesn't accelerate a car, if FORCE cousing movement it change into work, and work over time = POWER.

The FORCE from jet engine pushes a plane forward. But as we know (or I'am wrong) FORCE don't push enything, only POWER couses acceleration. This is why I'am confused

Engine power from the car goes to the gearbox etc... and finally to the wheels.
The wheels begin to rotate, and this rotation (acceleration) is cousing by TORQUE at the wheels or POWER at the weels (i think power)?

What is correct and what is wrong with what I write?

 

[berkeman]

only POWER couses acceleration.

But F = ma...

 

[vysqn]

But F = ma...

So F = ma works in jet engine but why we don't use it at car engine? - and we combine "ma with distance over time" to calculate power ?

 

[jack action]

The force causes the acceleration ($F = ma$);
The power determines the speed you can achieve with the given force ($P = Fv$).

So, if you want to keep a constant acceleration, as the velocity increases, you will have to increase the power ($P=mav$).

Usually, you have a limited amount of power (i.e. a limited mass fuel rate to burn), so the available acceleration will decrease as the velocity increases.

 

[berkeman]

So F = ma works in jet engine

I think it's more accurate to look at the momentum of the exhaust from the jet or rocket to calculate the "thrust". What links have you been reading about how jets and rockets work? Have you read about Specific Impulse yet?

 

[Dale]

As we know, POWER is what accelerate a car, FORCE itself doesn't accelerate a car

As was pointed out by @berkeman and @jack action this is incorrect. It is the force that causes the acceleration by F=ma, not the power. For instance, when accelerating from rest the acceleration is non zero and the force is non zero, but the power is zero. If it were power that caused acceleration then nothing at rest could ever start moving.

 

[Rive]

So F = ma works in jet engine but why we don't use it at car engine? - and we combine "ma with distance over time" to calculate power ?

It depends on the actual problem you want to solve that what tool is practical. If you do it right then calculations with power might represent a shortcut when force will depend on speed, for example (for most vehicles, it does and it is quite complicated, actually). Yet, it is still force what causes acceleration - by calculating with power you just skipping some complicated math.

 

[vysqn]

At 20:56 this guy talk about what we feel when we accelerate a car. He said that power cause acceleration not moment of force (torque)... Goshh I got so little brain to understand this ...:)

 

[CWatters]

What you feel is the reaction force from the seat due to acceleration. What causes that accelerstion is the net force or torque acting on the car.

He goes further to say that it's the power that determines the torque so you are really feeling the power. That's true but don't confuse power with maximium power. Petrol engines typically have discrete gear ratios so you cannot always operate the petrol engine at the right rpm to deliver max power. So torque isn't always at a maximum.

Things are slightly different for an electric motor. They can generate close to max power over the whole of the speed range including low speeds where more of that power is available to accelerate the car (less needed to overcome drag). So an electric car can sometimes accelerate faster than a petrol car even though its maximum power output is lower.

 

[Dale]

At 20:56 this guy talk about what we feel when we accelerate a car. He said that power cause acceleration not moment of force (torque)..

The guy is wrong. This is why we use the professional scientific literature as our primary source here

 

[jack action]

We can only feel forces. Our brains can interpret those as accelerations.

The reason why power is considered the source of acceleration is because power is actually the source of the force. It is fairly simple to state $a=\frac{F}{m}$ and end it there. But having an acceleration necessarily means the velocity increases. As the velocity increases, we need more power to maintain the same force ($F=\frac{P}{v}$). Otherwise - keeping the same power input - the force will drop, therefore the acceleration will decrease as well.

This is why we can state «We need power to accelerate» ($a=\frac{P}{mv}$) even though it is the force that causes acceleration. With half the power, you will get half the acceleration as the velocity increases because you will only produce half the force (comparing the motion at the same velocity). When in motion, we need power to get a force.

 

[Dale]

This is why we can state «We need power to accelerate»

Not if v=0.

You need force to accelerate, that is it. The force is provided by the torque, so it is the instantaneous torque that provides acceleration.

The problem is that people look at engine specifications and think that the max torque or the max power is the instantaneous torque or power. It is the instantaneous torque that gives acceleration at any point, but the instantaneous torque may be less than the max torque and the instantaneous torque may be limited by the max power.

 

[jack action]

Not if v=0.

Yes, but if you constantly stay at zero then you're not accelerating. As soon as you'll reach v=0⁺, power will become relevant.

 

[Dale]

Yes, but if you constantly stay at zero then you're not accelerating. As soon as you'll reach v=0⁺, power will become relevant.

Sure, but it directly disproves the claim that you "need power to accelerate". You do not because acceleration can be nonzero while power is zero.

Again, instantaneous torque is the only parameter that is directly related to the instantaneous acceleration at all times.

 

[jack action]

The claim is that you need power to get a force while in motion. And you need a force to get an acceleration.

When comparing vehicles in motion, I can assure you that the one with the greatest power can always accelerate faster than the other one. In this context [NoteToSelf]always state the context[/NoteToSelf], you need power to accelerate.

 

[russ_watters]

We need power to accelerate
...
Yes, but if you constantly stay at zero then you're not accelerating. As soon as you'll reach v=0⁺, power will become relevant.

Sure, but it directly disproves the claim that you "need power to accelerate". You do not because acceleration can be nonzero while power is zero.

Again, instantaneous torque is the only parameter that is directly related to the instantaneous acceleration at all times.

While I agree more with Dale, let me try to spin the statement in a way that creates agreement:
We need linearly increasing power to continue the same rate of acceleration (not including losses) as speed increases.

To say that in car terms: almost any car will jump off a starting block at at a high acceleration. I had a 92 horsepower coup that I could spin the tires on if I let off the clutch to fast. But in order to keep accelerating rapidly after the initial jump, you need high horsepower. Indeed, the purpose of the gearing is partly to enable constant power acceleration (except for a Tesla, which can do constant torque acceleration).

 

[Dale]

But in order to keep accelerating rapidly after the initial jump, you need high horsepower

I am ok with that, because if you want to keep accelerating then you need to maintain a high torque and the faster you go the more power is required for the same torque. It is still the instantaneous torque that causes the acceleration, but the instantaneous torque is limited by the maximum power (at high speeds) rather than the maximum torque (which is the torque limit at low speeds).

 

[Dale]

The claim is that you need power to get a force while in motion.

The claim from the video is “power is what accelerates the car so it is always the power that you feel”. That claim is wrong.

 

[jack action]

The claim from the video is “power is what accelerates the car so it is always the power that you feel”. That claim is wrong.

Agreed. Full disclosure: I didn't watch the video.

 

[vysqn]

So " always power you feel" is wrong. It should be like this:
Engine power generate a force which accelerate (and force you feel) a car because F = ma.
More power = more force pushing car forward.

Is that correct?

 

[jack action]

So " always power you feel" is wrong. It should be like this:
Engine power generate a force which accelerate (and force you feel) a car because F = ma.
More power = more force pushing car forward.

Is that correct?

Yes.

 

[AZFIREBALL]

It is all a matter of definition. You say force does not cause acceleration. This is incorrect.

Force causes the acceleration of a mass (F=ma) by definition.

Let us look at an ideal case. If you apply a force to an unrestrained object(mass), the mass will accelerate. It will not just give it velocity but, it will accelerate. This is hard for some people to see because every object they encounter is restrained to some extent by external conditions.Take the case of an object (mass) in outer space. If you apply a force to this mass, it will start to accelerate. As long as this force is applied, it will continue to accelerate. Not just move forward at a constant velocity but, accelerate (ever increasing velocity). This concept is counter intuitive to those of us who live in an environment where every object we encounter has constraints of some sort. The constraints maybe, friction, gravity, air resistance, etc. Anything that keeps it from moving (obtaining a velocity).In our environment we are required to continue to apply a force, just to keep the object moving at a constant velocity due to the constraints. To get an object to accelerate we must add additional force over and above this minimal force. We all know, to keep a car with a dead battery moving, it requires that a substantial force be continually applied to just overcome the constraints.A car’s engine changes rotation, into torque, at the wheels thus causing forward movement.

This torque is converted to a force at the axel level by the reaction of the lever-arm(radius of the wheel) pushing against the friction existing between the tire and the road surface, after all constraints have been overcome. This is the FORCE that pushes the car forward.

 

[vysqn]

Yes.

Torque from the engine is limited by revs. We can use CVT transmision to accelerate forever but there we hit a point where all forces (friction , air resistance, etc) will stop car and that's the car top speed.
Is that Correct?

So let's go back to jet plane where we can also use 2nd Newton's law.
If Jet engine produce constant trust that means constant acceleration (If mass doesn't change and there is no air resistance)
But there is a point when air resistance is so big that plane doesn't accelerate any more and that is top speed of the plane.
We can calculate power if we want using P = Fv .
Is that correct?

 

[russ_watters]

So " always power you feel" is wrong. It should be like this:
Engine power generate a force which accelerate (and force you feel) a car because F = ma.
More power = more force pushing car forward.

Is that correct?

Yes.

No! Jack, this is the argument you were having with @Dale again. The current form of the OP's statement does not mention speed. The relationship between force and power requires an unstated assumption about speed.

You may recognize the unstated assumption, but it isn't at all clear the OP does so we should not be agreeing with any answer that leaves it unstated.

 

[vysqn]

For instance, when accelerating from rest the acceleration is non zero and the force is non zero, but the power is zero. If it were power that caused acceleration then nothing at rest could ever start moving

This is start to be more confused than it was:)
So torque is moment of force, a parameter that is directly related to the instantaneous acceleration at all times
So why we even calculate power? If power doesn't generate a force which pushing car forward?
Please don't tell me that average 100Nm between 2000-4000RPM (from 50-70km\h) will accelerate car faster than average 50Nm between 8000-10000RPM (from 50-70km\h)

 

[russ_watters]

So torque is moment of force, a parameter that is directly related to the instantaneous acceleration at all times

Right.

So why we even calculate power? If power doesn't generate a force which pushing car forward?

Because we also care about speed and fuel usage and engine displacement (size).

Please don't tell me that average 100Nm between 2000-4000RPM (from 50-70km\h) will accelerate car faster than average 50Nm between 8000-10000RPM (from 50-70km\h)

Here you're confusing engine torque with wheel torque.

 

[vysqn]

This is Jason Fenske who is mechanical engineer said:
at 2:10 that "power is what gives you speed, what gives gives you acceleration"
and at 7:05 "how fast will a car be able to accelerate, what will its top speed be - that comes down to power"


This is John Cadogan who is also mechanical engineer and he said:
at 12:40 "power at the wheels produces force which pushes you forward making you accelerate and speed which you acquire along the way as a consequence"

So who is right...

 

[Dale]

Newton is right. Sorry, none of these videos is teaching you correct physics.

 

[vysqn]

How is that possible that those 2 enginers are wrong?

 

[russ_watters]

How is that possible that those 2 enginers are wrong?

As a fellow mechanical engineer, it's disappointing. They are being sloppy. When they say "acceleration", they are talking about an average over a variety of speeds, which is a twist on simply stated acceleration.

Sometimes the sloppiness doesn't matter, but here it lead you from a description that was a little sloppy to an understanding that was very, very wrong.

Also, my understanding is there is a furious but silly debate about torque vs power among car guys.

 

[vysqn]

Newton is right. Sorry, none of these videos is teaching you correct physics.

if it is true, it is ruining my worldview. I start to learn some physics just for fun some time ago because I was curious how torque and power works. And those guys looking trustable for me...
And now I feel crushed...

 

[Dale]

How is that possible that those 2 enginers are wrong?

Note, the requirements of PF, as I have already mentioned above, are that all posts on PF must be consistent with the professional scientific literature. That means textbooks and peer-reviewed papers. Youtube videos are not peer-reviewed and they are not vetted. They are often of low quality scientifically, as here.

I am sure that if those engineers were preparing a scientific publication then they would have been more correct in their statements. But it is not our goal to correct all youtube errors so it is pointless to send lots of videos containing such errors. We recognize that they exist and that is precisely why the acceptable standards here are higher.

 

[vysqn]

Note, the requirements of PF

What is PF ?

And what proffesional scientific literature You suggest me to learn about power, torque force etc?

 

[jack action]

@vysqn :

I'll try to demonstrate the problem from another perspective. You start with the engine and try to figure out where the power/torque goes. It is in my opinion that it is best to look at what needs to be achieved to reach the desired objectives.

There is a vehicle (car or plane or whatever) of mass $m$, it has a velocity $v$, an acceleration $a$ and some resistance $R$ (drag, rolling resistance, etc.).

To maintain this set up, you must also have a force $F$. The force $F$ can be found with the following relationship:
$$F = R + ma$$
But, there is also the notion of power $P$ that is important. The following relationship must also be respected:
$$P=Fv$$
What does this means?

Whatever power source you have (combustion engine, jet engine, electric motor, horses or humans pulling the vehicle; anything), it must be able to produce the force $F$ and the power $P$.

Usually, the force $F$ is easy to achieve (with a gearbox for example), no matter what the power is; no matter whether this power is composed (at the source) of 'force' or 'velocity'. But power is maintained through any change (not considering minor losses) due to the principle of conservation of energy.

What happens if $a=0$? Then $F=R$ and $P=Fv$. If this is the maximum power you can produce, then $v$ is your maximum velocity.

If you can increase the power by $\Delta P$, then - at this velocity $v$ - the force $F$ will increase ($F+\Delta F=\frac{P+\Delta P}{v}$), thus the acceleration $a$ will increase ($0+\Delta a=\frac{F+\Delta F -R}{m}$ or $\Delta a=\frac{\Delta F }{m}$), which in turn will increase $v$, setting you to a new equilibrium. Note that you might need to do some transformations along the way to make sure $P=Fv$ for the vehicle (like changing the gear ratio for example).

What happen if $v=0$? Then $F=R+ma$ and $P=0$. This means that as long as the power source can produce the force $F$, you are OK. How much power does it [keyword]needs[/keyword] to produce? None.

So a 5 hp lawnmower engine can theoretically produce the necessary force to reach the same acceleration that a 10 000 hp dragster engine can produce ... at $v=0$ and only at $v=0$. Note that in reality, there might be so much losses in the transmission that the force $F$ will not be reached (In fact, either $R$ or $m$ will be greater in some way).

But if the engine produces, say, 300 hp at $v=0$, where does it all go? It goes into wasted heat (the tires spin, clutches slip, etc.), mechanical energy (stored in rotating parts because of inertia) or elastic energy (parts will deform).

What I'm saying is that instead of starting with the engine and trying to figure out what you can do with it, try to analyze what is required by the vehicle.

 

[Baluncore]

What is PF ?

You are there. PF is www.physicsforums.com

There is a different language out there where the identical words have completely different meanings.

When I pointed to the two faded blue marks on the tachometer and asked if they were the equal power points I was told; “No, those are the equal torque points”, and that “it is not power until it gets to the back wheels”. I chose NOT to argue, so the inspector granted my license upgrade.
I do know that you should change gear at equal power points, which happen to be equal torque points at the back wheels, but they are not equal engine torque points. The engine RPM and gear ratio steps have a lot to do with that.

 

[Dale]

Please don't tell me that average 100Nm between 2000-4000RPM (from 50-70km\h) will accelerate car faster than average 50Nm between 8000-10000RPM (from 50-70km\h)

Why not. That is exactly right. A higher average torque directly means a higher average acceleration. Note, I am talking about torque at the wheels, not torque at the engine.

Edit: and I am assuming the RPM is the engine RPM and the mass and wheel size is identical. If you intended something different then my answer would be different

 

[jim hardy]

You started this thread a few days ago
https://www.physicsforums.com/threads/is-engine-torque-a-static-force.959297/#post-6083015
and were shown the error of your ways

But you are trying to hold to to your old mistaken preconceived word salad ideas. Forget them they're only confusing you. And a lot of other car enthusiasts too.
Here's what Abbe de Condillac said about such thinking about 250 years ago:

"Instead of applying observation to the things we wished to know, we have chosen rather to imagine them. Advancing from one ill founded supposition to another, we have at last bewildered ourselves amidst a multitude of errors. These errors becoming prejudices, are, of course, adopted as principles, and we thus bewilder ourselves more and more. The method, too, by which we conduct our reasonings is as absurd; we abuse words which we do not understand, and call this the art of reasoning. When matters have been brought this length, when errors have been thus accumulated, there is but one remedy by which order can be restored to the faculty of thinking; this is, to forget all that we have learned, to trace back our ideas to their source, to follow the train in which they rise, and, as my Lord Bacon says, to frame the human understanding anew.

In an automobile you feel acceleration which is in direct proportion to engine torque, (of course multiplied by gear ratios and wheel radius, and both of those are constant so long as you stay in any particular gear...and don't have a torque converter ahead of the gearbox )

Power is NOT in proportion to torque , it's in proportion to PRODUCT of Torque and RPM.
Horsepower = 2π X Torque_ft-lbs X RPM / 33,000

PS
That Condillac quote comes from a good introduction to straight thinking by Lavoisier. It's at https://web.lemoyne.edu/giunta/lavpref.html , and is worth digesting.old jim

 

[jim hardy]

Power is a RATE of doing work. So it inherently includes a unit of time. Something per second or minute, see horsepower equation above.
Torque is not a rate it's just a force albeit a force of rotation not straight line pull. No time necessary .

 

[jim hardy]

And what proffesional scientific literature You suggest me to learn about power, torque force etc?

start here ?
http://hyperphysics.phy-astr.gsu.edu/hbase/force.html
Search on words you do not understand, and even those you think you do.

 

[jack action]

In an automobile you feel acceleration which is in direct proportion to engine torque

This is wrong. The acceleration is in direct proportion to wheel torque. The difference is rather important in this case.

Please don't tell me that average 100Nm between 2000-4000RPM (from 50-70km\h) will accelerate car faster than average 50Nm between 8000-10000RPM (from 50-70km\h)

Why not. That is exactly right. A higher average torque directly means a higher average acceleration. Note, I am talking about torque at the wheels, not torque at the engine.

Why not? Because the vehicle goes at the same speed in both cases (The OP did take the time to mention it). This means that the wheel torque will be 1.5 times higher [= (50 * 9000) / (100 * 3000)] in the first case compare to the other, which is exactly comparing power outputs. This shows that a vehicle's wheel torque is proportional to power when compared at the same car velocity (as long as there is a velocity, i.e. $v \neq 0$). Your first 2 sentences are in direct contradiction with your last sentence.

For any advisors who would like to continue debating on this thread, I'm suggesting reading this https://www.physicsforums.com/threads/answering-simple-questions.953955/. At this point, the answers given are not helpful at all. They bring up confusion and frustration. Also, here is a little reminder of what can be found on PF home page (my emphasis in green text):

The Physics Forums Way
We Value Quality
• Topics based on mainstream science
• Proper English grammar and correct spelling
We Value Civility
• Positive and compassionate attitudes
• Patience and diplomacy while debating
We Value Productivity
• Disciplined to remain on-topic
• Honest recognition of own weaknesses
• Solo and cooperative problem solving

 

[Dale]

This is wrong. The acceleration is in direct proportion to wheel torque. The difference is rather important in this case.

Yes! I agree. Torque is not a conserved quantity, and gearing ratios can dramatically change the torque from the engine to the wheel. Power on the other hand is conserved (energy rather) so gearing ratios only change power indirectly through making the engine more or less efficient (neglecting small mechanical losses).

Your first 2 sentences are in direct contradiction with your last sentence

It isn't a contradiction. I specified wheel torque. He was unclear.

 

[jack action]

It isn't a contradiction. I specified wheel torque. He was unclear.

Even if he was specifying wheel torque & rpm, the fact that both cases have the same linear velocity means that the wheel radii are different, thus the forces at the wheel contact patch are still in proportion to the power:
$$P_{out} = P_{in}$$
$$Fv = T \omega$$
$$F = \frac{T\omega}{v}$$
Case 1:
$$F_1 = \frac{T\omega}{v} = \frac{50\ N.m \times 9000\ rpm}{60\ km/h} = 7500 \frac{N.m.rpm}{km/h}$$
Case 2:
$$F_2 = \frac{T\omega}{v} = \frac{100\ N.m \times 3000\ rpm}{60\ km/h} = 5000 \frac{N.m.rpm}{km/h}$$
[Too lazy to do unit conversions ]

Still in such case, the propulsive force is 1.5 times larger.

I'm specifying that because conservation of energy plays a major role here. In the debate «power vs torque», it is the great forgotten on the «torque» side. They understand Newton's 2nd law but refuse to acknowledge the principle of conservation of energy. I don't want to give them more ammunition when they'll read this thread and say: "Scientists on PF say only torque matters in acceleration, power is meaningless".

It must be clear that this is not up for debate and that it is based on fundamental scientific principles.

 

[Dale]

Even if he was specifying wheel torque & rpm, the fact that both cases have the same linear velocity means that the wheel radii are different

Oops, you are right, good point here. I was also not clear. I was assuming identical vehicle mass and wheel size, hence the specifications would be wheel torque and engine RPM.

I believe that most of the problems in the discussion come from lack of clarity. Engine vs wheel. Average vs peak vs max. Comparison criteria, etc.

They understand Newton's 2nd law but refuse to acknowledge the principle of conservation of energy

Energy is conserved, certainly. But that is not the question here. The question is about acceleration, and at all times for a given vehicle acceleration is directly proportional to wheel torque, not power. Conservation of energy is a great principle, but not the relevant one for the specific question of acceleration.

I have already explained the clear contradiction at rest, but even at high speed there is another clear contradiction. At high speeds (but neglecting dissipation) assuming a continuously variable transmission you could accelerate at constant power. In doing so your acceleration would decrease. Your power would be constant but your wheel torque would decrease, in exact proportion to the decreasing acceleration.

My assertion that torque (wheel) causes acceleration is correct, and in no way should be misconstrued to indicate that energy is not conserved. Power is important for acceleration, but only indirectly as when the maximum available power is what limits instantaneous wheel torque.

 

[cjl]

It's important to note though that at all times at a given vehicle speed, acceleration is directly proportional to horsepower. Wheel torque is almost never directly measured or referenced when discussing cars, and discussions like this lead to misconceptions like the very common believe that engine torque matters more than horsepower.

 

[Dale]

It's important to note though that at all times at a given vehicle speed, acceleration is directly proportional to horsepower.

Not at rest. From a stand-still power is 0 regardless of acceleration.

Wheel torque is almost never directly measured

Yes, that is a problem. Also, there is often a confusion about instantaneous torque vs max torque.

discussions like this lead to misconceptions like the very common believe that engine torque matters more than horsepower.

But the alternative leads to misconceptions on the physics as demonstrated by the OP. Here I am concerned about fostering correct physics much more than fostering correct purchasing decisions.

 

[cjl]

Not at rest. From a stand-still power is 0 regardless of acceleration.

Yes, but acceleration from a standstill is a very small subset of the "how fast will my car accelerate" case, and is complicated by a number of other factors.

But the alternative leads to misconceptions on the physics as demonstrated by the OP. Here I am concerned about fostering correct physics much more than fostering correct purchasing decisions.

I feel like the constant "no, power doesn't determine acceleration" in this thread is leading to far more misconceptions about physics than my statement above. In addition, knowing that it's proportional to power is fundamentally more useful, since a car's power is easily determined from its specifications and is independent of things such as driveline configuration and gear ratio. It's much simpler for a driver to know that to maximize acceleration, they must simply select whatever gear puts the engine closest to max power rather than suggesting that they must calculate wheel torque based on varying gear ratios and engine RPM.

For an example of how this can be misleading, you very confidently stated that the statement in the video in post #8 was wrong. You are wrong about this. The video is absolutely correct. At best, your statement is extremely misleading, since the video was quite clear about its statement that horsepower determines rate of acceleration (correct), and acceleration determines the reaction force between you and the seat of the car (also correct).

Fact: At all nonzero speeds, acceleration is directly proportional to power to weight ratio, and inversely proportional to speed

 

[Dale]

knowing that it's proportional to power is fundamentally more useful

Except that it is not proportional to power, it is proportional to power divided by speed (ie torque) and speed changes during acceleration. So stating that acceleration is proportional to power is kind of dodgy since the constant of proportionality is not constant. That isn’t the usual relationship meant by “proportional”.

At all nonzero speeds, acceleration is directly proportional to power to weight ratio, and inversely proportional to speed

Sure, because power divided by speed is directly proportional to wheel torque.

Look, I am not familiar with this apparently heated debate. I have no stake in it and I am just teaching physics. The power people have apparently convinced the OP of some incorrect physics as you can see from the OP. So overemphasizing power is not the be-all end-all solution.

Instead of having a power vs torque argument, wouldn't it be better to actually teach the physics of how power and wheel torque are not independent concepts but are closely related? Then you can show them how to calculate torque from power and thus figure out the acceleration.

 

[jim hardy]

For any advisors who would like to continue debating on this thread, I'm suggesting reading this https://www.physicsforums.com/threads/answering-simple-questions.953955/. At this point, the answers given are not helpful at all. They bring up confusion and frustration. Also, here is a little reminder of what can be found on PF home page (my emphasis in green text):

If i was uncivil i hereby extend my apology
was trying to be a bit forceful to break down what i perceived as a mental barrier , that's all

old jim

 

[jack action]

At high speeds (but neglecting dissipation) assuming a continuously variable transmission you could accelerate at constant power. In doing so your acceleration would decrease. Your power would be constant but your wheel torque would decrease, in exact proportion to the decreasing acceleration.

Yes, but if you double that constant power, you will double the acceleration at any speed. And this is the only way you can achieve that.

Look, I am not familiar with this apparently heated debate. I have no stake in it and I am just teaching physics. The power people have apparently convinced the OP of some incorrect physics as you can see from the OP. So overemphasizing power is not the be-all end-all solution.

Instead of having a power vs torque argument, wouldn't it be better to actually teach the physics of how power and wheel torque are not independent concepts but are closely related? Then you can show them how to calculate torque from power and thus figure out the acceleration.

I see the problem now from your perspective. So you are unfamiliar with the problem and don't see how it is to "teach" a «torque» person about the importance of power in vehicle acceleration? Let me get you up to speed with this thread. The fun starts with post #15 with OldYat47 (and, yes, it goes all the way to post #100). This type of discussion has been going on forever in the automotive community and the web forums are filled with those. You might appreciate more why you must be careful about the wording you choose when entering this debate.

 

[Dale]

Yes, but if you double that constant power, you will double the acceleration at any speed. And this is the only way you can achieve that.

Agreed, because doubling the power will double the torque. There is no power vs torque objection there.

So you are unfamiliar with the problem and don't see how it is to "teach" a «torque» person about the importance of power in vehicle acceleration?

Having “torque” people and “power” people is silly. They are not independent quantities.