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#31
10-27-2005, 04:20 AM
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Re: Speed Limits
[ QUOTE ]
[ QUOTE ] [ QUOTE ] The force due to drag is what I meant to put there. Replace m with A. [/ QUOTE ] (1/2) AV^2? [/ QUOTE ] Pretty sure you're going to need a drag coefficient and the density of the fluid in the there somewhere as well. [/ QUOTE ] Yes; that's what I was prompting him for as as it stands the units aren't even right. 
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#32
10-27-2005, 04:31 AM
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Re: Speed Limits
[ QUOTE ]
[ QUOTE ] [ QUOTE ] [ QUOTE ] The force due to drag is what I meant to put there. Replace m with A. [/ QUOTE ] (1/2) AV^2? [/ QUOTE ] Pretty sure you're going to need a drag coefficient and the density of the fluid in the there somewhere as well. [/ QUOTE ] Yes; that's what I was prompting him for as as it stands the units aren't even right. [/ QUOTE ] ~ Cd*rho*A*v^2
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#33
10-27-2005, 04:45 AM
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Re: Speed Limits
I tend to do 90 on my bi weekly motorway trips and there are still a lot of people who pass me, the 70mph limit on the motorways most people ignore and the police supposedly will only stop you if you are going over 85. I get 35mpg out of my car doing these speeds the published figures are 37.7mpg so the loss isnt that significant.
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#34
10-27-2005, 04:53 AM
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Re: Speed Limits
[ QUOTE ]
[ QUOTE ] [ QUOTE ] The force due to drag is what I meant to put there. Replace m with A. [/ QUOTE ] (1/2) AV^2? [/ QUOTE ] Pretty sure you're going to need a drag coefficient and the density of the fluid in the there somewhere as well. [/ QUOTE ] Is it ok if I just leave it out so that we can see that the force is proportional to the square of the speed? k, thanx
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#35
10-27-2005, 04:54 AM
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Re: Speed Limits
[ QUOTE ]
[ QUOTE ] [ QUOTE ] [ QUOTE ] The force due to drag is what I meant to put there. Replace m with A. [/ QUOTE ] (1/2) AV^2? [/ QUOTE ] Pretty sure you're going to need a drag coefficient and the density of the fluid in the there somewhere as well. [/ QUOTE ] Is it ok if I just leave it out so that we can see that the force is proportional to the square of the speed? k, thanx [/ QUOTE ] But there should also be a term to account for the "shape" of the object.
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#36
10-27-2005, 05:15 AM
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Re: Speed Limits
[ QUOTE ]
[ QUOTE ] [ QUOTE ] [ QUOTE ] [ QUOTE ] The force due to drag is what I meant to put there. Replace m with A. [/ QUOTE ] (1/2) AV^2? [/ QUOTE ] Pretty sure you're going to need a drag coefficient and the density of the fluid in the there somewhere as well. [/ QUOTE ] Is it ok if I just leave it out so that we can see that the force is proportional to the square of the speed? k, thanx [/ QUOTE ] But there should also be a term to account for the "shape" of the object. [/ QUOTE ] A*Cd? Fd= .5 pv^2 A*Cd
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#37
10-27-2005, 05:28 AM
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Re: Speed Limits
[ QUOTE ]
[ QUOTE ] [ QUOTE ] [ QUOTE ] [ QUOTE ] [ QUOTE ] The force due to drag is what I meant to put there. Replace m with A. [/ QUOTE ] (1/2) AV^2? [/ QUOTE ] Pretty sure you're going to need a drag coefficient and the density of the fluid in the there somewhere as well. [/ QUOTE ] Is it ok if I just leave it out so that we can see that the force is proportional to the square of the speed? k, thanx [/ QUOTE ] But there should also be a term to account for the "shape" of the object. [/ QUOTE ] A*Cd? Fd= .5 pv^2 A*Cd [/ QUOTE ] The shape will be taken into account in the drag coefficient (roughness etc.), the velocity vector (part of flow that is perpendicular to the object in question) and A, the surface area of the object in question.
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#38
10-31-2005, 03:35 PM
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Re: Speed Limits
most not all mind you, vehicles will get their best fuel mileage at the lowest speed that they can run in their highest gear(lowest gear ratio) while not lugging the engine.
in passenger cars thats about 30 or 35 mph. up to about 55 they get resonable mpg for the engine. over 55 it starts to really drop your mpg for each mile per hour you increase. thats mostly from wind resistqnce. as the faster you go wind drag proportionatly gets more dramatic. in montana we had no speed limit. only reasonable andprudent was what it was called. but too many people went way too fast and lots of accidents happened. and more deaths from the faster speed. the straw that broke the camels back was when some mechanic won in court a ticket for going well over 100 as he claimed his car was set up for it and he was a pro. he won and made the law look follish. so they lowered it to 70 on all country roads. which made it worse and even little roads that were curvy that 45 was too fast became 70 mph speedways. they just transferred the deaths from the hiways to the small local roads. politics at work.
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