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ytyourclothes@p.zapto.org
science forum beginner

Joined: 11 Jun 2006
Posts: 16

Posted: Fri Jul 21, 2006 1:25 am    Post subject: Re: Do The Math: Save Gas By Driving Slower

 Quote: Work = Force X Distance. So obviously it takes more force to drive faster in a car, and the same distance is traveled regardless of how fast you are going. So if we reduce the speed limits we will save money and gas!!!!

1) Think your claim through to the end: v -> 0
2) Reconsider.

cordially

Y.T.

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Shmuel (Seymour J.) Metz1
science forum Guru

Joined: 03 May 2005
Posts: 604

Posted: Thu Jul 20, 2006 10:36 am    Post subject: Re: Do The Math: Save Gas By Driving Slower

07/17/2006

 Quote: Work = Force X Distance. So obviously it takes more force to drive faster in a car,

It's not obvious, or even true. The force required is the sum of that
needed for acceleration and that needed to overcome friction. Friction
is highly nonlinear.

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mika
science forum beginner

Joined: 18 Jul 2006
Posts: 1

Posted: Tue Jul 18, 2006 10:49 pm    Post subject: Re: Do The Math: Save Gas By Driving Slower

Jason Pawloski wrote:
 Quote: virtualadepts@gmail.com wrote: Work = Force X Distance. So obviously it takes more force to drive faster in a car, and the same distance is traveled regardless of how fast you are going. So if we reduce the speed limits we will save money and gas!!!!

Why oh why are you forcing this crap on sci.math? At least we're used
to these fantasies of yours on alt.magick!

 Quote: As has been shown countless times, reducing speed limits won't save money on gas. Reducing driving speed, however, would. There is a very big difference between the two. Your analysis is flawed, and no argument is ever as clear-cut as this. For instance, if you drive faster, you might use less gas if you accelerate slower than if you drive slower but peel out when you accelerate. Where does this appear in your analysis? Also, if you drive at a higher rate of speed, you can engine break for a longer distance which uses less gas than moving at a particular constant velocity. Also, if you drive a straight segment that has lights timed at 45 MPH, and you drive at 35 MPH, you will hit lights and will unlikely save on gas. The real problem is the existence of non-linear factors that depend on velocity. Wind resistance is the most notable. Also, if your engine uses x amount of gas at 1.5 kRPMs, it certainly does not use 2x amount of gas at 3 kRPMs.

All great points. I'd also like to add that engines are designed to
operate at peak efficiency at a specific speed, which varies from manuf
to maunf and certainly is not the slowest the engine is capable of. It
should say in a car's specs what speed the rated fuel efficiency is
based on (naturally, they'll test at the optimum speed to be able to
list the best possible fuel efficiency).
Aristos
science forum beginner

Joined: 23 Mar 2006
Posts: 14

Posted: Tue Jul 18, 2006 10:29 pm    Post subject: Re: Do The Math: Save Gas By Driving Slower

 Quote: Work = Force X Distance. So obviously it takes more force to drive faster in a car, and the same distance is traveled regardless of how fast you are going. So if we reduce the speed limits we will save money and gas!!!!

Time is not a factor of work, so you can't go "faster" with that
equation.
DGoncz@aol.com
science forum Guru Wannabe

Joined: 25 Oct 2005
Posts: 122

Posted: Tue Jul 18, 2006 11:22 am    Post subject: Re: Do The Math: Save Gas By Driving Slower

 Quote: Work = Force X Distance. So obviously it takes more force to drive faster in a car, and the same distance is traveled regardless of how fast you are going. So if we reduce the speed limits we will save money and gas!!!!

I did a little paper for Dr. Majewski's PHY 298 Seminar and Project on
propulsive efficiency of a bicycle. When you include basal metabolism
in total enery cost of travel, a peak is found for propulsive
efficiency independent of slope, with a correction for head/tail wind.

The idling problem is similar. Idling costs money. So does ownership. I
haven't expanded my analysis of car travel, but there are incentives to
keep moving. Ask any local cabbie.

Let's reduce the speed limit to 0. We'll all save on gas. :)

Doug Goncz
Replikon Research
Seven Corners, VA 22044-0394
science forum beginner

Joined: 15 Jun 2006
Posts: 15

Posted: Tue Jul 18, 2006 6:36 am    Post subject: Re: Do The Math: Save Gas By Driving Slower

 Quote: Work = Force X Distance. So obviously it takes more force to drive faster in a car, and the same distance is traveled regardless of how fast you are going. So if we reduce the speed limits we will save money and gas!!!!

I think we should increase the speed limit to 90, and simutaneously go
on the metric system.
Tom111
science forum Guru Wannabe

Joined: 21 Jan 2006
Posts: 173

Posted: Tue Jul 18, 2006 4:51 am    Post subject: Re: Do The Math: Save Gas By Driving Slower

 Quote: Work = Force X Distance. So obviously it takes more force to drive faster in a car, and the same distance is traveled regardless of how fast you are going. So if we reduce the speed limits we will save money and gas!!!!

Why should we care if we save money and gas or not?

Materialist! Miser!

Use it up. Give it all away.
mensanator@aol.compost
science forum Guru

Joined: 24 Mar 2005
Posts: 826

Posted: Tue Jul 18, 2006 4:36 am    Post subject: Re: Do The Math: Save Gas By Driving Slower

 Quote: Work = Force X Distance. So obviously it takes more force to drive faster in a car, and the same distance is traveled regardless of how fast you are going. So if we reduce the speed limits we will save money and gas!!!!

Flunked the class on gear ratios, eh?
jpawloski@gmail.com
science forum beginner

Joined: 04 Dec 2005
Posts: 7

Posted: Tue Jul 18, 2006 4:34 am    Post subject: Re: Do The Math: Save Gas By Driving Slower

 Quote: Work = Force X Distance. So obviously it takes more force to drive faster in a car, and the same distance is traveled regardless of how fast you are going. So if we reduce the speed limits we will save money and gas!!!!

As has been shown countless times, reducing speed limits won't save
money on gas. Reducing driving speed, however, would. There is a very
big difference between the two.

Your analysis is flawed, and no argument is ever as clear-cut as this.
For instance, if you drive faster, you might use less gas if you
accelerate slower than if you drive slower but peel out when you
accelerate. Where does this appear in your analysis? Also, if you drive
at a higher rate of speed, you can engine break for a longer distance
which uses less gas than moving at a particular constant velocity.

Also, if you drive a straight segment that has lights timed at 45 MPH,
and you drive at 35 MPH, you will hit lights and will unlikely save on
gas.

The real problem is the existence of non-linear factors that depend on
velocity. Wind resistance is the most notable. Also, if your engine
uses x amount of gas at 1.5 kRPMs, it certainly does not use 2x amount
of gas at 3 kRPMs.

Jason Pawloski
science forum beginner

Joined: 19 Feb 2006
Posts: 18

 Posted: Tue Jul 18, 2006 3:48 am    Post subject: Do The Math: Save Gas By Driving Slower Work = Force X Distance. So obviously it takes more force to drive faster in a car, and the same distance is traveled regardless of how fast you are going. So if we reduce the speed limits we will save money and gas!!!!

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