Black/Navy blue disk(ovoid as visible from the side) demonstrates instantaneous acceleration or some form of a “cloaking”mechanism.

In 2010 I was with my family at a barbecue. I was younger and was mainly hanging around with the other kid who was there, a girl about my age that I had known for some time. It was the 4th of July and we stepped outside to look at the fireworks being set off near by. I remember hearing fireworks go off behind us in the direction of her backyard where the parents were. We both turned around so we could see them, but when we looked in the sky, there was a silent, black disk floating slowly across the sky. I used to build model military/civilian aircraft when I was a kid, so I knew, and still know, what a human aircraft looks like. It was not a blimp. Not a balloon, as it’s movement was perfect, unlike the characteristic bobbing associated with loose balloons(I should add, it was not particularly windy). I could not gauge its size. This next part is a bit corny, but this is what happened. The disk moved slowly until her neighbors(the home behind her’s) chimney was blocking it from view. We quickly repositioned ourselves around her neighbors house, but it was gone, we couldn’t see it anywhere and believe me we looked. We told our parents and they didn’t believe us. This changed my perspective on everything.