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comment by Devac
Devac  ·  11 days ago  ·  link  ·    ·  parent  ·  post: SpinLaunch conducts first test of suborbital accelerator at Spaceport America

Man, it's really too late/early for this, but I suspect the problems begin around here:

    KE = 1/2 Iomega^2. SHIT. Frickin' moments of inertia? I = L/omega. L = M x V x R. Uhhhm, M is mass is 1kg. V is angular velocity. R is radius around the centroid - hey we got all this shit!

Angular momentum is a vector quantity, and it's almost too easy to lose track of components and frames of reference even without not only having a wrong formula for L, but a wrong formula for the magnitude of L.

  L = r x p (L, r, p vectors) ; p = m * v (p and v vectors)

  |L| = m * r * v * sin(angle between component vectors r and v)

On a first glance, your model can be simplified to a rod spun a distance r around an axis, parallel axis theorem style, but I'm gonna take this one in pieces. Updates inbound.





nil  ·  11 days ago  ·  link  ·  

My high school physics teacher used to carry a stamp around that said "momentum is a vector" and stamp it on students' papers. Seems that issue came up a lot.

He also had his sample of uranium-238 taken away by a certain government agency (I think Canadian Nuclear Safety Commission)?

I miss that class.

kleinbl00  ·  11 days ago  ·  link  ·  

LOL you and your vectors. Speaking as a credentialed engineer, allow me to say that physicists insist on vectors, engineers just look for what makes the part break. Which is always a scalar. ;-)

Devac  ·  11 days ago  ·  link  ·  

But, in the end, isn't scalar just a trivial tensor?

Seriously, though: I know it can be annoying, but if my pedantism received anything over the last couple of months, was vindication.

kleinbl00  ·  11 days ago  ·  link  ·  

(sometimes you work harder when goaded)