Why do two textbooks give different critical speed formulas?

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jayadds
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In one textbook, it says that the critical speed is the minimum speed at which an object can complete the circular motion. It gives the formula:
v = square root of (g*r)
However, in another textbook it says that the formula is:
v = square root of (2*g*r)

How can there be two different types of equation for critical speed? Which one is correct?
It's funny because they both start off with the same Newton's second law: w+n = mv^2/r

For the first equation, they said that critical speed occurs when n = 0 whereas for the second equation, they said that critical speed occurs when n = w. Which one is correct?
 
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There may be a typo in the 2nd textbook, or perhaps you are reading it out of context.
Check again.