wndrlst

For roughly $57 per annum I'd prefer to refuel 1/2 as often even though I pass plenty of gas stations. At 5 minutes+ per fill-up & 100+ fill-ups per year (conservatively), I value my time more than the savings.

STEELTOWN

Equations get us in the ballpark and then its testing to see what additional items need to be covered. Computers also play a big role in crunching the long involved values. That equation for air resistance is legitimate. It takes into account the density of air, the coefficient of drag - .29 for a Tl among other things. You are right, that equation does not address cross winds, etc among other things. The Fluid Dynamics equations address the wind characteristics a bit finer, turbulent versus laminar, etc. Better answers take longer, thus the more involved equations. But if you need a quick and dirty answer, equations like the ones stated will do.

jpt

I'm a programmer, not an electrical engineer. Never took circuits, and you've yet to actually (correctly) call my physics wrong...

The original point of my post was the term negligible can not be used unless you know the answer. [...] So working 50 weeks out of the year, I will spend (@$3.10 gallon gas) an extra $57.00. That is low ball because we didn't work in accerlerating that weight over the course of my commute/year. So I guess there are a few people here who have better things to do with $57.00 than to toss it out the window, we can't all be money making Electrical Engineers.[/QUOTE]
Okay, let's be conservative and call it $100 a year. That's what I call negligible. I spend more than $100 a year on, well, everything I spend money on. I spend more than $100 a year on M&Ms. That's negligible.

No, I haven't invented new science. It's simple: if you accelerate a mass to a velocity, that energy can overcome the losses of air drag and tire rolling resistance just as burning more gas can do the same. Therefore if you accelerate more mass to the same speed, you can let off the gas earlier when you want to come to a stop and the energy that you put into the extra mass will then be "recovered" by not requiring you to burn more gas to slow down (on an electric car, you can actually recover the energy more directly by using it to charge your battery). It's really simple; are you sure you know how to do anything more than copy random formulae out of the physics book that must be sitting near you?

$57 a year for a year's worth of filling up your gas tank every 400 miles rather than much more often. That's where the 100 lbs (weight of 17 gallons of gasoline) came from, too. Of course it's an overestimate since on average I only have half a tank of gas and this is assuming I have to pay the price of carrying around a full tank all the time.

So should we take out our spare tires, or only the magical hundreds of pounds of useless crap that we're somehow stupid enough to be leaving in there for no reason at all?

Filling gas as often as I do is already a pain in the ass. Who in the world would do it twice as often for $4.75 a month? (Still not sound negligble to you?)

Why did you have so much crap in your trunk to begin with? You could have been saving pennies a day! Hell, that's almost as much as I find lying in the sidewalk when walking around downtown!

youngTL

When possible a controlled experiment will do even better, like the one I did. Modeling only gets you so far. And by the way, the solutions to the NS equations require DAYS on a supercomputer to get a few solutions (there are infinitely many confined to a finite space...I think they trace out a strange attractor).

jpt

But at typical highway speeds, in practice, air resistance on cars is well dominated by the quadratic term. A cubic term starts to become significant over about 80mph. These two rules of thumb do not of course apply to an arbitrarily shaped object flying through the atmosphere, but all cars basically look alike.

Still Water

Sometimes a cigar is just a cigar.

sauceman

I'll buy into this.

STL

That doesn't just go for obese people. Remember muscle weighs more than fat, so people like those shown in your avatar are carrying around a bunch of needless weight too!

If you really want to talk about pushing/pulling around of bunch of needless weight, you need to start with all the people that have SUVs without ever really using all that room.