Shiny, black teardrop shaped craft that moved horizontally and vertically before zooming away diagonally.

On May 1, 1990, a group of myself and four other friends were playing hackey sack (foot bag) on the Ethel McKnight School playground in East Windsor, NJ when we spotted a strange, teardrop shaped, shiny black object in the sky.  It made no noise that we could hear.  
It was hard to tell how close or far away it was, or how big or how fast it was moving since we did not know what it was.  By process of elimination we determined that it had to be a U.F.O.
It moved horizontally as well as vertically across the sky as well as staying still. It was no aircraft we had ever seen or seen since. 
After about ten minutes it zoomed diagonally, up and out of sight very fast.