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prometheum
 
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Quote:
Originally Posted by JimmySal View Post
Is the vehicle burning fuel?

Do tires stay the same shape as speed increases?

Does the rotational inertia of various components in the vehicle remain constant as speed increases?

What about friction constants in bearings?

all those have nothing to do with how much force gravity exerts on the vehicle all the variables you listed have nothing to do with the effect gravity exerts on it, and would remain the same whether you were going uphill, downhill or on a flat road

the only thing that affects how much force gravity exerts on the vehicle is the mass and if you want to get technical how far away the object is away from the center of the earth
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Old 01-15-2007, 08:39 PM prometheum is offline  
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Clear enough?

Yeah. Your thinking acceleration I was thinking top speed.
Old 01-15-2007, 08:41 PM Loote is offline  
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Newton's second law states that force is equal to the differential change in momentum per unit time.

All the questions I asked have to do with the momentum of the vehicle. Translational and rotational. Whether they are significant or not in the grand scheme of things is irrelevant. They still exists.

Seriously, don't fuck with me. I do this shit for a living.
Old 01-15-2007, 08:42 PM JimmySal is offline  
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Yeah. Your thinking acceleration I was thinking top speed.

If you get right down to it though, the ability to create a motive force at the road surface and therefore an acceleration is what dictates top speed.
Old 01-15-2007, 08:43 PM JimmySal is offline  
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Yeah. Your thinking acceleration I was thinking top speed.

More like he read the thread and was talking about what rang3 asked, and you were going off on some 'dropped from a helicopter' hypothetical
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Old 01-15-2007, 08:44 PM [H]ard|On is offline  
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onewheeldoin200
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Quote:
Originally Posted by JimmySal View Post
No, it won't. Rotational inertia is what stops something from moving down hill quickly. Since the vast majority of the vehicles weight is translating rather than rotating, weight is largely irrelevant. You could roll 2 identical vehicles down a hill, one unladen and one with half a ton of ballast, and they'd both end up at the bottom at the same time.

Under power however, the vehicle with ballast would arrive second. The vehicles would have the same torque output and therefore the same force on the road pushing them along. Since one is more massive than the other, the resulting acceleration would be less for the heavier vehicle. Acceleration due to gravity is the same on both vehicles, add up the accelerations, the net acceleration is less on the heavier vehicle, it arrives second, and you're still a .

Clear enough?

yup

in scalars, a = sum(F)/m = (mg)sin(slope_angle) + Fengine = (g)sin(slope_angle) + Fengine/m

So, in the first term mass doesn't come into play (ie. the hill doesn't matter from one car to the next), and in the second as mass increases the acceleration becomes less.
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Old 01-15-2007, 08:47 PM onewheeldoin200 is offline  
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I elected to forgo the formulae in my explanation because I raised quite a bit of rabble when I told everyone how F doesn't equal ma. Not really anyway.
Old 01-15-2007, 08:51 PM JimmySal is offline  
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prometheum
 
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Quote:
Originally Posted by onewheeldoin200 View Post
yup

in scalars, a = sum(F)/m = (mg)sin(slope_angle) + Fengine = (g)sin(slope_angle) + Fengine/m

So, in the first term mass doesn't come into play (ie. the hill doesn't matter from one car to the next), and in the second as mass increases the acceleration becomes less.

just making sure we're on the same page here

acceleration though the motor becomes less as mass increases because the force the motor exerts is constant at a given rpm

acceleration due to gravity remains the same because the force gravity exerts on vehicle increases proportionally to the vehicle's mass
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Old 01-15-2007, 08:51 PM prometheum is offline  
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I elected to forgo the formulae in my explanation because I raised quite a bit of rabble when I told everyone how F doesn't equal ma. Not really anyway.

lol
I got it at least.....
people jsut dont now how varied something as simple as F=ma can be
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Old 01-15-2007, 08:53 PM wwilliam54 is offline  
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yep
Old 01-15-2007, 08:53 PM JimmySal is offline  
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lol
I got it at least.....
people jsut dont now how varied something as simple as F=ma can be

Yeah, I got a 0 on a system dynamics quiz back in the day because the prof. asked us to write Newton's second equation of motion.

I wrote F=ma

Nevar forget.
Old 01-15-2007, 08:54 PM JimmySal is offline  
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wwilliam54
 
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yep


The more mechanics I learn, the more I realize Newton makes even Einstien look like retard
Truly THE giant among all the lesser men that have lived.
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Old 01-15-2007, 08:55 PM wwilliam54 is offline  
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#102  

wwilliam54
 
Quote:
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Yeah, I got a 0 on a system dynamics quiz back in the day because the prof. asked us to write Newton's second equation of motion.

I wrote F=ma

Nevar forget.
lol
in statics its F=ma

kekeke
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Old 01-15-2007, 08:55 PM wwilliam54 is offline  
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Quote:
Originally Posted by JimmySal View Post
I elected to forgo the formulae in my explanation because I raised quite a bit of rabble when I told everyone how F doesn't equal ma. Not really anyway.

what rabble?

what's wrong with F = ma?

zomg I'm smarter than newton?
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Old 01-15-2007, 08:57 PM I Am 'fullvietFX's Bitch is offline  
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JimmySal
 
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lol
in statics its F=ma

kekeke

In statics, dynamics, the first 3 physics classes I took, and in Design of Machine Elements f was equal to ma

Not anymore though. System Dynamics, High Performance Vehicle Engineering, Vehicle Dynamics, Advanced Systems Modeling, and Modern Physics cured that.

now, F = d(m * v) / dt

lol

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Originally Posted by boshi View Post
what rabble?

what's wrong with F = ma?

zomg I'm smarter than newton?

The rabble? nothing I couldn't handle

F=ma doesn't have provisions for changing mass or changing acceleration, as is frequently seen in race cars (or airplanes or spacecraft if thats your bag). There isn't anything WRONG with F=ma per se, it just isn't the whole picture.

Nobody is smarter than Newton.

Last edited by JimmySal; 01-15-2007 at 09:01 PM..
Old 01-15-2007, 08:58 PM JimmySal is offline  
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