Recent content by Kricket

Situation: a car moving quickly down the road with a window open. Car reference frame: the air outside is moving, thus has lower pressure, thus the air inside the car will be sucked out the window. World reference frame: the air in the car is moving, thus has lower pressure, thus the...

When you apply a force to an object, be it a polygon or otherwise, you do two calculations: 1. Apply the force to the center-of-gravity (COG) 2. Take the cross product of the radius to the point of application, with the force, to obtain the torque Why, you might ask? Think of the...

Ah, no, sorry, no funny mixing of references in the cross product. :) Reference frames are a real PITA. Intuitively, what does this quantity represent? If I just have some random object in space with no angular acceleration, the formula seems to suggest that torque will be non-zero...

Thanks, DH, for writing that all out. So what you're saying is, for example, if I had a teapot that I threw into the air, and I use the Earth as my fixed world reference frame, (and we ignore translation for the time being) then I would pick "I" as the earth-frame, "R" as the teapot-frame, and...

jostpuur: thanks for your reply, although I think I'll have to look it over when I have more time! D H: thanks also...so, if I understand correctly, the derivation would go like (for an object centered at P): \textbf{q}_{obj} = \textbf{P}_{world} + \textbf{q}_{world}...

Hello all, I'm sure you all know the standard relation between torque and angular acceleration: \tau = I\alpha However, in reading a doc on kinematics this weekend, the author gave the following formula for torque: \tau = I\alpha + \omega \times L My question is, from whence...

Probably an easy one... So, I understand the idea of precession on a gyroscope: we've got the angular velocity vector, the angular momentum vector (same direction but times the inertia tensor), then a torque is applied => change in L in the direction of torque. I'm thinking of the example...

Yeah, I know they're PDEs and a big pain in the poop-chute...I'm a computer/math guy and by "chug" I meant, write some complicated program that approximates a solution for a given tiny dt (and d-whatever else) a few thousand times, and see what comes out. Alternatively, I've heard that...

Hello all, Still at my frisbee modeling program, I started to ask myself how I could get better approximations of stuff like COP versus angle-of-attack, drag/lift coefficients, etc. I've been checking out the Navier-Stokes equations because I understand they can be used to model fluid flow...

Yeah, when I put in extra torque in front of the disc, the simulation (eventually...) causes it to tilt to the left. But I'm still having trouble getting a realistic trajectory. Even with exaggerated torque numbers (ok, too exaggerated and the thing won't even fly...but everything up to that...

I was just using torque as an example to illustrate the meaning of the cross product. Spin (or rather, angular acceleration) does indeed come from force; however, in 3 dimensions you have not only how fast you're spinning, but also what you're spinning around (the axis of rotation). The torque...

I've studied a good bit of mathematics, so I can give you the mathematician's perspective on 1.5 of your questions. :redface: Mathematically, the "dot" product (or inner product) is necessary to introduce the concept of an angle in a metric space. Without it, you only have distance, but no...

Thanks for the reply. I can experimentally see what you're saying - when I put in exaggerated figures of side-torque, the simulation actually ended up turning so that it faced straight away from the thrower (instead of sideways). I assume this is because the rotation of the disc causes the...

Hello all, Sorry for the long post. Skip to the line for the relevant part. As a longtime ultimate frisbee player, and also a computer programmer, I'm trying to write a program to simulate the flight of a frisbee for any given real-world conditions. I've read through the 5 or so papers I...