I’m still baffled by the combustion engine I don’t go fast enough to think stiffness makes a difference I drive a 3 cylinder geo metro part of the time so that shows my taste and the only herts I need to know is rental cars and music. But I love learning new things I didn’t realize you could relate these things and it is cool to see the progression
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I have a lot better understanding of engines than of correlating stiffness with frequency. Right now I seem stuck on ironically thinking stiffness is a very flexible term. 
I’ve seen this demonstrated on a machine I believe is known as a ‘Spintron’. They basically construct a model of an engine with viewing ports and drive it with an electric motor and record the results with high-speed photography. It’s amazing seeing things like poppet valves you thought were quite rigid moving around like rubber when driven to high speeds. 
Reciprocating engines fascinate me. Before Formula 1 imposed a rev limit engines were turning more than 19,000 RPM. In a 4 stroke engine that means each cylinder was inducting a fuel/air charge, compressing it, burning it, and exhausting the combustion gases more than 150 times per second.
Mind boggling! And the sound of a V-10 engine doing that was amazing!
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Going off topic here. Does anyone else hate RPMS? I have no good mental idea of a minute. 150Hz is much more natural to me than 19,000 RPMS. It’s easier to convert to the period, and I can more easily visualize it. But the bigger number looks better in a brocure, I guess.
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I’m the exact opposite, I find mechanical things much easier to visualize than say a circuit. When I hear someone designing on the go saying things like we’ll need a few resistors of value ‘x’ here and there and a coupla diodes over there and a new, improved LSMFT chip in the middle I’m just amazed. I think it’s a good thing, it’d be a really boring world if everyone was the same. And I have to say, the damage an engine part can do when it leaves its position at thousands of RPM is quite impressive in a strange kinda way.
A hertz is a cycle per second, and Rpm is just cycles per minute…so RPM/60 = Hertz. 8^)
I’m not saying mechanical vs. electrical. Just that describing a motor in rotations per minute doesn’t make as much sense to me as describing it in rotations per second. Maybe it makes more sense with something like 100RPMs vs. 102RPMs.
I know that. It’s just not natural to think about it that way. I don’t like dividing by 60.
What’s even wackier than RPM is inches per minute, although perhaps it has its own logic: if you have IPM and RPM then you know inches per revolution, which divided by the number of teeth tells you your cut per tooth. Maybe that was useful in 1950 before calculators were everywhere.
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Or 1850, when you had to decide whether to beat the children, or offer them extra gruel to make the machines go faster…
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You have to admit, people did some pretty amazing work when slide-rules were the calculators of the day. I marvel at aircraft development between the Wright Brothers in 1903 and Chuck Yeager in 1947. 
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