Speed Pertaining to Circular Motion

  • Thread starter Coop
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Units for Speed Pertaining to Circular Motion

Hi,

So v=ω*r

Where v = velocity in m/s
ω = angular velocity in rad/s
r = radius in m

But I am confused...the units don't match! What happens to the rad?

m/s = (rad/s)*s

My textbook doesn't explain it, it simply does calculations like (56.5 rad/s)(0.030 m) = 1.7 m/s and the rad disappears. I have a feeling I am missing something obvious o_O. Any help?

Thanks,
Coop
 
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Answers and Replies

  • #2
D H
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The measure of an angle θ, in radians, is defined as the ratio of a circular arc subtending that angle θ to the radius of the circle. Angles thus have units of length per length. In other words, angle is a unitless quantity. Using radians makes the constant of proportionality one when computing arc length, or when computing speed along a circular path.
 
  • #3
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In other words, rads is not a unit. It's just a label.
 
  • #4
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Cool, thanks a lot guys, I wish my book explained that :p
 

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