Subject: Why can potential energy due to gravity be ignored on a vertical spring

Im a junior in high school and im in currently in honors physics.  My teacher 
asked us a question that he himself did not know the answer to.  In our physics 
book the same equation is used for a vertical as well as a horizontal spring.  
In this conservation of energy equation it simplifies to   V= the square root 
of k/m      why, in this equation for the vertical spring can the potential 
energy due to gravity be ignored.  Why would this not affect the equation at 
all.  Also, what would the correct equation to determine the velocity of a 
spring at equilibrium after maximum displacement...  preferebly using the COE 
equation.  Any help on this subject would be appreciated

Re: Why can potential energy due to gravity be ignored on a vertical spring