quote:

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You just indicated that you missed the entire point of my post.

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How so? You asked why "us engineers" didn't mathimatecly test the feasibility of your scenaro:

quote:

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I was referring to the idea that assuming an indestructible plane and conveyor belt and a conveyor belt capable of infinite speeds, could you run the conveyor belt fast enough to prevent the plane from taking off? (in essence, using just the friction generated from the plane wheels moving at super speeds).

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And I pointed out (mathematically) that the speed of the conveyor belt is not a variable in the friction equation.

where:

f = friction
m = plane mass
g = gravity constant
c = coefficient of friction

f = mgc

I don't know how to make it any simpler than that.

quote:

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The only force that the conveyor is applying to the airplane is dynamic friction. Dynamic friction is found by multiplying the Normal force (which on a level surface would be equal to the airplane's weight) by the coefficient of dynamic friction. Varying the speed of the conveyor in no way factors into the equation.

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dynamic friction (rolling resistance in this case) increases with velocity...

the tire deforms, air is pumped around inside the tire, the faster this happens, this takes more energy and means more rolling resistance as the velocity increases.

in a perfectly efficent world, where the tire doesn't deform, and the interaction between the tire and the ground is 100% efficent, there is no rolling resistance at all...

but when the conveyor is traveling at some awfully fast, nearly infinite speed, (as stated earlier 6 or 7 lyps) you will have enough rolling resistance to counteract the thrust of the engines...this velocity will vary by plane.

Glad to see somebody finally saw the light, NA...

quote:

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I don't know how to make it any simpler than that.

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Idiot. My point was that it took a non-engineer to come up with a way to mathematically solve this problem.

Plus, you have yet to mathematically prove that ALL sources of friction are moot.

I think the intelligence in the thread peaked somewhere around page 27-30 and we are currently in a recession. I actually feel dumber after reading the last 10 pages. Its a rapid decrease.

oh and page 54.

In all fairness to some of my fellow posters, we've never considered you the sharpest tool in the shed, so your opinion is moot.

quote:

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dynamic friction (rolling resistance in this case) increases with velocity...

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Wrong, it decreases. Look it up.

I did last time...get up to speed...

check page 20-30 somewhere...links and all

you're trying to say that the faster you apply compression cycles to a rubber baloon, the less energy it takes to apply them?

power is a force applied at a distance over a given time... [ft*lb/s] is HP with different units. The limit as time approaches 0 from the positive side is +infinity...

simpler, the power required to do the same work an a shorter ammount of time increases. -OR- to be specific to this case, the power required to complete the compression/deformation of the tire in one revolution would double if the time it was done in was cut in half.

If you are referring to a rolling resistance coefficent chart, you must look and see if your lines are assuming a constant velocity.

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Impossible to build an infinite speed treadmill, so that argument is moot.


NEXT!

What if I slowed time down enough to the point where even a slowly moving conveyer reached relatively infinite speeds?

[This message has been edited by NeuroticAg (edited 2/1/2008 2:15p).]

Impossible for YOU to do that, NA.


NEXT!!

I'll take a pound of brisket, and two hot links with a drink.

You don't know me! You don't know what I can and can't do!

Idiots. The whole infinite speed thing is moot. A plane doesn't require infinite speed to take off, so the conveyor would never need to be going that fast.

Your mom goes that fast!

quote:

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Your mom goes that fast!

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Which is a good thing because then it feels like we lasted longer than we actually did.

quote:

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In all fairness to some of my fellow posters, we've never considered you the sharpest tool in the shed, so your opinion is moot.

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The fact that i have been considered at all makes me warm and fuzzy.

quote:

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Idiots. The whole infinite speed thing is moot. A plane doesn't require infinite speed to take off, so the conveyor would never need to be going that fast.

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who said anything about the plane going an infinite speed?

the conveyor would be going really really really really really really really really really really really really really really really really really really really really really really really really really really really really really really really really really really really really really really really really really really really really really really really really really really really really really really really really really really really really really really really really really really really really really really really really really really really really really really really really really really really really really really really really really really really really really really really really really really really really really really really really really really really really really really really really really really really really really really really really really really really really really really really really really really really really really really really really really really really really really really really really really really really really really really really really really really really really really really really really really really really really really really really really really really really really really really really really really really really really really really really really really really really really really really really really really really really really really really really really really really really really really really really really really really really really really really really really really really really really really really really really really really really really really really really really really really fast because with friction and rolling resistance factored in, the graph of c in the equation x+c=x would not be linear...c would in fact be a quatratic in the form of (-x^2+ax+c), which means that the equation x+c=x would be true for two values of x...0 and one other.

What if it was a really, really, really tiny airplane and a really, really, really, really huge conveyor belt?

[This message has been edited by Red Skye (edited 2/1/2008 3:03p).]

I hope that isn't a sexual metaphor!



I'm sorry if it is...

What if the conveyor belt velocity was relative to my cousin?

I just cried a little. *sniffle*

What if the conveyor belt were in Plainview?

Your mom's in plain view!

Ouch!

Only if you keep feeding the thing quarters.

That makes no cents whatsoever.

quote:

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the power required to do the same work in a shorter amount of time increases. -OR- to be specific to this case, the power required to complete the compression/deformation of the tire in one revolution would double if the time it was done in was cut in half.

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Correct, and in our scenario, that power is supplied by the conveyor belt; the plane is not affected at all, as its contribution to the wheel rotation does not change. Sorry, try again.

Once again, the frictional force (or rolling resistance) acting against the airplane is:

f = gmc

where c is the coefficient of dynamic friction, or in this case, coefficient of rolling resistance.

frictional coefficients are usually assumed to be constant in simple problems like this, but since you insist on making things complicated: as the wheel speed increases, the temperature of the wheel bearings increase. The coefficient of rolling resistance decreases with increased temperature.

quote:

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who said anything about the plane going an infinite speed?

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The original question implied that the conveyor's maximum speed would only be the take off speed of the plane. Therefore, the people arguing over whether an infinite-speed conveyor would prevent the plane from taking off are moot.

quote:

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Correct, and in our scenario, that power is supplied by the conveyor belt; the plane is not affected at all, as its contribution to the wheel rotation does not change

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So, if you run the conveyor and leave the plane's engines at idle or off, the plane will not move? you're kidding...

the opposing forces of the engines and the conveyor are what make the wheels spin in the first place. Without the opposition of the planes engines, there would be no motion, energy or heat besides what the conveyor produces moving the plane backward.

The friction in the bearings is still negligible as far as my claim goes, and I continue to use the assumption of a frictionless bearing. I am simply talking about the rolling resistance of an inflated rubber tire. If we were talking about a train, you'd be correct. However, the difference between the equations and assumptions for steel on steel and rubber on concrete are too different to compare in a problem like this.

The original problem stated nothing about the conveyor traveling at the takeoff speed of the plane... it was worded that the conveyor simply matches the speed of the plane in the opposite direction. if IIIHorn or somebody would be so kind to link or quote the original "will it take off" thread you can see for yourself.

It looks like I picked the wrong day to quit sniffing glue...

quote:

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The original problem stated nothing about the conveyor traveling at the takeoff speed of the plane... it was worded that the conveyor simply matches the speed of the plane in the opposite direction.

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Yes, this means that the maximum speed of the conveyor will be the take off speed of the plane like I said earlier, smart guy.

are you measuring ground speed of the plane, or wheel speed?

I'm measuring wheel speed...

Engineers and physicists are jumping off bridges this weekend.

quote:

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Rex, your thread made me sad. I have like one strand of hope left. I'm one Bush speach away from offing myself.

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Don't do it, man. I'm sorry! This thread and that one both make puppies and kittens cry.

this thread could use a pron blast