# Rotational Velocity

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Velocity (linearly) I know is measured in meters. What's rotational velocity measured in? I mainly need to know because I'm making a DJ program, and I already have a 3D vinyl rotating precisely at 33 1/3 rpm in real time, and I'm trying to add physics to it for scratching and other stuff.

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Since velocity is meters per second, I'd assume rotational velocity is measured in degrees per second. Just a random guess.

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In physics at least, usually radians per second. 33 1/3 rpm is about 3.5 radians per second.

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That's what I'm thinking.

Rotating at 33 1/3 rpm, you are looking at 199.999999 degrees per second, which is 3.333333 degrees per frame. Works flawlessly on mine. For the rotation, I simply multiplied the degrees per second by the elapsed seconds. That way there, it doesn't matter how fast or slow your framerate is. It'll always rotate 33 1/3 rpm.

And no, it's not 3.5. It's 3.333333 ;)

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Here is why.

360 degrees * 33 1/3 rpm = 11999.999999 degrees per minute

11999.999999 degrees per minute / 60 seconds = 199.999999 degrees per second

199.999999 degrees per second / 60 FPS = 3.333333 degrees per frame

Just thought I'd clear that up

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Quote:
 And no, it's not 3.5. It's 3.333333 ;)
Mm, I think you're confused about the units involved. 3.33 degrees per frame (at 60 hz) is (approximately) 3.5 radians per second. 'Radians per second' and 'degrees per frame' are not the same thing.

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I was using radians. How do you think I came up with such results? I always use radians in my 3D graphics using this formula:

Degree * PI / 180

Ok switch my terminology from degrees per whatever to radians per whatever. :D

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Ok, well I'm not sure where the initial confusion was, but:

33 1/3 rpm =
200 degrees per second =
3.33 degrees per 1/60th second

If that all looks good to you, then we're in agreement :)

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Or simply 1 RPM is 2 pi radians and then So multiply any number in rev/min by 2 pi

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