Rotating Mass – Marketing Fallacy?

[Tim Lewis]

I think breakfast is just a marketing ploy by the cereal companies. I don't think anyone really needs to eat in the morning. After all, what have you been doing all night? Sleeping, right? You shouldn't need to eat after that. Lunch makes sense, you've been working for a few hours. Same thing with dinner. Breakfast, though, that's just a fallacy.

[Pete Muller]

In other words, the kinetic energy of a rolling body is equal to the sum of translational and rotating components.


Arrrghh! Finally!!!

Thanks Joseph!

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PM

[Larry Hayashigawa]

Bottom Line

The original post was questioning whether decreasing the rotational inertia improved acceleration. McFadden believes it does, from a theory standpoint he is wrong but from a practical perspective he is right. Acceleration does increase but it does not have nearly the effect that many believe it does.

Checking out of this thread

Larry

[Mike Goebel]

That was a sweet example Joseph


Mike MFG.

[joseph hollinger]

[joseph hollinger]

[Mike Goebel]

[Charles Pou]

I agree with Scott's premise, not because of physics, but because of economics.

The law of diminishing returns comes to mine. As a racing kart for example is developed, you pay more and more for less and less results. At some point you realize you are paying big $'s for very little, if any increase in speed.

For F1/ NASCAR where millions are at stake, cost is no object. Kart racing as a hobby is another matter....

As for Scott's physics, IMO it's flawed because it leaves out the energy to rotate the flywheel, it only accounts for the energy to move the flywheel down the track.

Continuing the example of 2 karts, each the same in all respects, except kart #1 has an extra 100# sitting in the seat and Kart #2 has a 100# flywheel mounted the rear axle. The flywheel is fitted with a niffty one way bearing (so as the kart moves forward the flywheel is rotated, but as the kart is slowed or stops the flywheel is allowed to freewheel).

Accelerate both karts over an equal distance and stop. Kart #2 should accelerate slower than kart #1, because it takes more energy to move 100# down the track and rotate it (as with kart #2), than to just move it down the track (as with kart #1).

When kart #2 comes to a stop, the 100# flywheel is still spinning and has significant energy that could be used, such as move the kart forward from a stop. On the other hand, the 100# weight in the seat of kart #1 has no such energy.

So where did the extra energy in the spinning flywheel come from? It came from the engine, same configuration both karts. Kart #1 used more of the available engine power to move the kart down the track so it should be faster.

Kart #2 wasted some of the available energy spinning the flywheel. In effect Kart #2 was less efficient using the available power for the intended purpose.

So, given the same amount of energy, the less you use to rotate moving parts, the more you have available to accelerate the kart down the track, and the faster you should be.

However, please don't get too carried away, or you may later realize you spent your retirement racing karts.

[Scott McFadden]

[quote="Larry Hayashigawa"]Bottom Line

The original post was questioning whether decreasing the rotational inertia improved acceleration. McFadden believes it does, from a theory standpoint he is wrong but from a practical perspective he is right. Acceleration does increase but it does not have nearly the effect that many believe it does.


Hold on there Larry that's not what I said at all. I said in short that as long as the total wieght of the kart is constant, reducing the rotational mass at the expence of ballast will make no difference to the kart's straight-line acceleration.

I was referring to the wheels brake rotors chains sprokets etc who's acceleration is 1:1 with the forward acceleration of the kart. The flywheel stuff was thrown in later and ads a degree of complication that you have addressed. But I would like to read your analysis of just the chasis rotating parts, disregarding engine parts for now.
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Scott

[Scott McFadden]

[quote="Pete Muller"]In other words, the kinetic energy of a rolling body is equal to the sum of translational and rotating components.


so..... if you increase the translational component by the same amount you deacrease the rotational component (take wieght off the brake rotor and add it to the back of the seat) kinetic energy remains unchanged
_________________
Scott

[Pete Muller]

[joseph hollinger]

[William Marenich II]

Acceleration of Gravity
At any distance r from a large circular body of mass M a smaller body of mass m will experience a gravitational force.

Applying Newton's Second (Fnet = ma) to the small object we can determine its acceleration if no other force are acting on the small mass m but gravity (Fnet = FG).



Acceleration of Gravity Near the Surface of a Large Body
Assume that a large body of mass M and radius R has a radically uniform mass distribution. The gravitational force on a small mass m at height h above the surface of the large body can be expressed as,



If h << R, then

If we neglect air resistance, then this is the net force acting on the mass m. Applying Newton's Second Law, Fnet = ma,

Because of its importance we usually give the acceleration of gravity due to the Earth a separate name,

* This equation does not depend upon the mass of the small object - the mass canceled out on both sides of the force equation. This proves that the acceleration due to gravity alone is the same on all objects independent of their mass, their size, their density, or even their speed.
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Danke,
William J. Marënich II

[Mike Goebel]

Yeah gravity, that's a good one. Like that exists. Next you will be telling the superposition principle for a rolling and translating mass doesn't exits.


Mike G.

[Scott McFadden]