Talk:Car speed, energy consumption and city driving

Nominate for delete

This article was nominate for delete but evidently no notice was added here.

Wikipedia:Articles for deletion/Car speed and energy consumption Johnjbarton (talk) 21:51, 19 November 2023 (UTC)

Essay like?

@Stuartyeates marked this article as unsuitable because it is essay like. I don't understand this claim. Can you help me with some specific issues? Johnjbarton (talk) 21:55, 19 November 2023 (UTC)

I came across the page on NPP and the structure seemed unlike an article. Stuartyeates (talk) 08:51, 20 November 2023 (UTC)

Thanks. However I don't know what an NPP is. What do you suggest would make it more like an article? Johnjbarton (talk) 15:17, 20 November 2023 (UTC)

Why doesn't this article redirect to Fuel economy in automobiles?

I would like to know why this article exists when we have Fuel economy in automobiles? What is the relationship?

Is this article devoted solely to cars? Speed? Seems like an unusual choice.

Is the intention to be a simpler version of Fuel economy in automobiles? Johnjbarton (talk) 22:05, 19 November 2023 (UTC)

Merge into Energy-efficient driving

I think moving this content in to Energy-efficient driving would create a better result for readers. Johnjbarton (talk) 23:30, 20 November 2023 (UTC)

Power

The article says

• The consumption of energy per second increases eightfold (23) if you drive twice faster.

However, at double speed the time one needs to cover a given distance is now 1/2, so the energy consumption is 4x. In other words the Power discussion has nothing to do with the relationship between car speed and energy consumption. Johnjbarton (talk) 16:21, 4 December 2023 (UTC)

The lead summarized the Power section with

• "The required power increases with the cube of the speed, so driving twice as fast costs theoretically eight times as much fuel per unit of time."

But again this is redundant information. Johnjbarton (talk) 16:22, 4 December 2023 (UTC)

@Johnjbarton Because of the cubic dependence of power on speed, a doubling of the speed leads theoretically to an eightfold increase of the power and so the energy consumption rate. The experimental data in the graph by Tennekes support the cubic relation at high speeds. It's just basic physics. Can you restore please the section you deleted? Thanks, Hansmuller (talk) 19:09, 8 December 2023 (UTC)

Sorry I disagree.

The graph shows the top speed dependence on power. As air drag resistance increases quadratically with speed, the force needed to overcome the resistance increases. Eventually, lower power cars cannot overcome the resistance: they reach their "top speed".

The graph is not related to energy consumption or city driving. It is related to car speed only in the sense of race car speed, not a topic of the article. That cars with high top speed are also comparatively inefficient is entirely a matter of economics, not physics. Electric cars for example have high power, high top speed, and yet they have outstanding energy efficiency.

The relationship between energy consumption and speed has already been established. This additional paragraph only adds confusion. Johnjbarton (talk) 20:02, 8 December 2023 (UTC)

@Hansmuller since the page was redirected you may have missed my replies here. Of course they don't help now, but I wanted you to know I replied. Johnjbarton (talk) 16:39, 9 December 2023 (UTC)

Acceleration

Unfortunately the Acceleration section appears to be Wikipedia:Original research.

The formulae given for the acceleration of a mass are all nicely referenced. But in Mackay's simple model the acceleration phase is where all of the thermodynamic loses occur. So by combining these two sources we get a distorted view.

In an attempt to make his model simple MacKay divides the total energy into acceleration, drag, and resistance. He has already established the total loss from the observed energy budget of cars. So he never talks about acceleration of a mass assuming 100% efficiency as implied by the article. The best cars are <25% so the section is wildly inaccurate. Johnjbarton (talk) 16:45, 4 December 2023 (UTC)

How could this section be "original research"? Standard mechanics is applied with a high school level numerical example, while using the formulae of the source MacKay. Thank you, Hansmuller (talk) 18:58, 8 December 2023 (UTC)

Yes, exactly my point. You are taking MacKay as a reference but then using formula for acceleration from another source. But MacKay is using the word "Acceleration" to name a phase in the energy cycle, not only the physics of car speed change. To put this another way, your calculation misses what is by far the biggest factor in energy consumption: the thermodynamic loses due to the inefficiency of the energy. For every 4 gallons of fuel, 3 of them go in to heat! This is the issue that many editor complained about: the 5% loss due to air drag is small compared to the engine efficiency issues. Yes, speed is an issue above some value but by far the engine efficiency is the main effect. Johnjbarton (talk) 20:16, 8 December 2023 (UTC)

City driving

Added a section on the practical topic of city driving, with repeated stop/start cycles, all from the book by MacKay. Cheers, Hansmuller (talk) 18:59, 8 December 2023 (UTC)