I was reading an article about automotive fuel economy and an engineer was making the point that to conserve gas, minimize acceleration because acceleration uses a lot of fuel.
It occurred to me that a physicist would say to minimize braking, because braking converts kinetic energy into heat.
They are both correct, and probably the more you brake the more you have to accelerate. But one focuses on when you’re using the fuel, and the other focuses on when you’re throwing away energy.
I don’t see that either discpline would focus exclusively on one fuel economy approach or another.
FWIW, I once read an SAE paper that analyzed fuel economy, and found that good fuel economy for urban driving correlates strongly with “microtrip” time. A “microtrip” was defined as travelling from one stopping point to another, e.g. the light turns green, you advance to the next traffic light, you have just completed one “microtrip.” Your entire journey from start to finsh would be composed of a series of microtrips. Long microtrip times are had by gentle accelerations, modest speeds, and (consequently) the least possible braking requirement at the end of each microtrip.
I don’t see that either discpline would focus exclusively on one fuel economy approach or another. Why wouldn’t both of them look at all the relevant factors?
FWIW, I once read an SAE paper that analyzed fuel economy, and found that good fuel economy for urban driving correlates strongly with “microtrip” time. A “microtrip” was defined as travelling from one stopping point to another, e.g. the light turns green, you advance to the next traffic light, you have just completed one “microtrip.” Your entire journey from start to finsh would be composed of a series of microtrips. Long microtrip times are had by gentle accelerations, modest speeds, and (consequently) the least possible braking requirement at the end of each microtrip.
Well, a physicist would be modeling the car as a frictionless sphere rolling along in a vacuum which doesn’t correlate well to my driving experience.
Braking is a form of acceleration ( specifically negative acceleration/deceleration). In your example, both the physicist and the engineer are advocating for the same thing - avoid acceleration!
You can say that again! 
Yes, but only the physicist is likely to use the word “acceleration” in that manner. An engineer, being more practical, would use “deceleration,” as that’s the term most people use, and thus would accomplish the advice job more easily.
I am an engineer, lol… :dubious:
An economist would simply assume a car that got better mileage.
The physicist might also need to consider acceleration part of the equation in terms of the efficiency of the engine at turning chemical energy into kinetic energy. The brakes are clearly 100% efficient in their conversion, but different acceleration methods might lead to different fuel consumption for the same increase in kinetic energy.
Perhaps they would gather their data, form their hypothesis, then turn the whole problem over to operations research who would analyze population distributions, male driving technique vs female technique, tall vs short, hilly vs flat, city vs highway then do a linear program to come up with a solution that works most of the time.
I’d hope one of them would ask why anybody expects gentle forward acceleration was better. In the case where the top speed is constrained (say, to be 55 mph because we’re on a highway), then the acceleration we use to achieve it should be using the engine at a speed and torque where its fuel use is most efficient, not smallest. For typical engines I think that’s at a major fraction of full power. In other words, the engine is definitely going to have to come up with the mechanical energy that the car stores in its motion at top speed, and it should do so at the most power efficient point on its curve, which IIRC is often at around 3/4 of full power.
Just look for that tattoo behind their left ear–engineers have a bar code, scientists are in Binary.