# Homework Help: How to calculate critical speed in circular motion?

1. Apr 13, 2012

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?

Last edited: Apr 14, 2012
2. Apr 15, 2012

### PhanthomJay

There may be a typo in the 2nd text book, or perhaps you are reading it out of context.
Check again.