The mislead of horsepower for over 200 years-thermal engines

[marius-ciclistu]

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Hello everybody.

I decided to share with you some conclusions, that I draw after a few months of studying the car's thermal engines and their transmissions.


First of all, I'll speak about my project, so you can better understand the reasons why I came to these conclusions.

In early 2016, I made an online calculator and comparator for tyre dimensions, based on their codes. The reason for doing that was that I needed a fast tool to compare tyre diameters, in order to choose enhancing performance dimension of tyres for rally sprint.

Then I did an online, tyre friction force calculator based on it's treadwear number, that shows only the friction force, the adherence being composed of, friction force and other components generated by the tyre profile and elasticity.

After that, in order to choose a cheap old stock car for rally, I made an online car transmission calculator and comparator, which I developed and improved through a period of several months. The results of this calculator, helped me draw the conclusions I'll be presenting you in this video.

While I was improving the transmission calculator, I realised that I can do an online car cost calculator, and that's what I did. It shows the real cost of owning and using a car and it is under the form money per 100 kilometers.

And finally, because I am a former performance cyclist and I was often asked the question: How should I use the bike's gears?, I made an online bicycle transmision calculator, but this will not be the subject of this video.

You can find the link to these online calculators and comparators in the below description.

And now, about the subject of this video: power, torque, force, mass and acceleration.

Isaac Newton's laws of motion are three physical laws that, together, laid the foundation for classical mechanics. They describe the relationship between a body and the forces acting upon it, and its motion in response to those forces.

Newton's second law states that force is equal to mass multiplied by acceleration. These will be the base things we will look upon, when talking about the dynamics of a car.

Now lets explain the other physical terms.

Power, from the force and acceleration point of view, is nothing but a formula. Watts equals newtons meter multiplied by radians per second. This can be transformed in other measuring units like horsepower etc.

Torque, is force multiplied by arm length. It's measuring unit is newton meter.
The torque graph or curve in relation with rotational speed, is given by the manufacturer but can be also deduced by measuring the force at the traction wheels' circumference on a dynamometer. That force is the traction force, and, according to Newton's second law, it should be the number one interest for us.

You can find more detailed explanations about power and torque on wikipedia.

Now let me tell you my conclusions.

1. The human body can feel only forces when a car accelerates. It can not feel power, nor torque!
2. Horsepower mislead the people's opinion about power since 1781, when James Watt patented a steam engine that produced continuous rotary motion. I bet many people think that their cars have hundreds of horses aligned in front of it. Wrong! If we are to asume the same principle as Watt did, the Horse Force can be defined as 735 Newtons. Consequently, for example, 107 horsepower can equal only maximum 10.6 horce force in first gear.
3. In physics, power is not synonymous with force. Consequently, horsepower is not synonymous with it's perception in peoples minds, horse force.
4. The only information that the maximum power can give us, if we know the power's formula, is an irrelevant torque value at an elevated rpm, nothing more, unless we think of the illusion of horses in front of our car.
5. In an ideal environment, the power at the flywheel is equal with the one at the wheel. This, among the one that horsepower creates mislead, is the second reason why the power was, or stil is, used to describe the thermal engine's characteristics.
6. The traction force at the maximum torque's rpm is bigger than the force at the maximum power's rpm. Consequently, the same thing can be said about the acceleration.
7. The maximum power doesn't give the shifting rpm, neither is the maximum torque. The shifting rpm is given by the torque curve and gear ratios, as you can see here, the gold colored lines must be as near as possible to the horizontal.
8. So, "power is a denatured mirroring of force and acceleration in thermal engines' regard."


My advice to you is:
Stop using power to describe a thermal engine's dynamic characteristics. Use torque instead, and if you talk about the engine plus transmission as a unit, use force and acceleration.

For more videos check out my youtube channel.

[marius-ciclistu]

P=W/t or P=E/t

(E and W is the same thing, energy).

It is normal that at higher rpm you need more energy in the same amount of time(say 1 s), but that doesn't mean for sure that you will get bigger torque in an Internal Combustion Engine. So if you need more traction force(=> bigger acceleration), saying that you need more torque is more specific than saying that you need more power, because the torque is force multiplied by a constant(arm), unlike power that is force multiplied by a constant(arm), multiplied by radians/second (which are NOT CONSTANT).

Or, a more relevant example:
F is 10 N
arm is 1 m
rpm is 1500

If you want to increase the force with 10% at 1500 rpm, you need to increase the torque by 10% at 1500 rpm which means increasing the power with 10% WITHOUT INCREASING the rpm.

But because in people's mind power can be increased by increasing the RPM it's more specific to say increasing torque than increasing Power.

[marius-ciclistu]

According to:
P(W)=T(Nm)*RS(rad/s)
P(W)=E(J)/t(s)
=> T(Nm)*RS(rad/s)=E(J)/t(s)

At 1 rad/s torque is considered power.
At 1 rad/s torque is considered energy/1s.
Power is considered energy/1s.

This is why, some physicists are saying that power is important, that power generates acceleration.
To mask torque and to encourage people on using power(horsepower) when talking about thermal engines.

But the part of power named torque is the part that generates traction force, that generates acceleration.

I wonder... why didn't they choose energy/s to promote the thermal engines...instead of power.... maybe because power and force are synonymous outside physics?