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      03-27-2008, 01:43 AM   #95

Drives: E92 M3 and Elise
Join Date: Oct 2006
Location: Land of the Microchip

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I am just guessing on the flywheel dimensions. I have seen a number of them out of cars so its probably not that far off. Weights typically run 10-22lbs. Still its really hard to estimate I since the shape is far from ideal.

Clutch friction (and tire slip) will consume some of the energy.

The calculation is much more complex. You have an unknown additional mass in the engine. There is the fact that the clutch engagement needs to be treated more like a physics collision (inelastic) and conservation of momentum needs to be addressed.

4: Yes. I simply wanted to make it clear that the energy has to go somewhere. I figured even footie could understand that. If you could easily just make energy disapear then things like falling off building wouldn't be a problem.

Originally Posted by swamp2 View Post
Nice analysis. Even if the numbers nor method are perfect the point is. A couple questions/corrections:

1. How close are your flywheel mass and radius? I know we don't have actual numbers and I know you are using estimates, but what is your guess?

2. The clutch friction will cause energy to not be conserved. However, even with a lossy joining of spinning disks angular momentum will be conserved. This is the begining of the correct calculation but since you have linear and angular momentum/energy it is a bit more complicated. I don't think you can even calculate the velocity change without a reasonable estimate of the total clutch back moment of intertia.

3. Even if energy were conserved, E = .5 * m * v^2 as you stated, but didn't you leave off the 2? So you are off by sqrt(2) = 1.4 in the 20.32 number. It is 1.4 x larger.

4. Footie either does not own a calculator or does not even understand the concept of a percentage (see the recent top speed threads), don't even bother with the forumlae and physics.

@ersin: Come on I expect better from a fellow physics person
Manual gearboxes, the rotary dial of cars.