I am looking for a children's short story about a scientist that invents a material that is pushed away from other matter. It accelerates away from gravity instead of towards it.
He makes several small (golf ball sized?) spheres of the material. He could wrap his fingers around a ball, but it would push his fingers out away from it, so it was hard to hold onto. If he let go of one indoors, it would zoom up to the ceiling.
If one got loose outdoors, it would zoom directly upward into the sky. Within a few hours it would leave the Earth-moon system. After a few days, it would zoom away from the Solar System constantly accelerating. After a million years, it would leave the galaxy.
He could put several balls into a chest harness that would let him hover. He had to balance the outward pull of the material against the gravitational pull of the Earth on his body. He also had one or more of his children hold onto to him.
One of his children wears a harness that just balances his weight against the upward acceleration so he can appear to be on the ground, but is actually slightly hovering. The child uses the harness to win events at a track and field competition.
This is not the movie Flubber, or the movie, The Absentminded Professor. It is a written short story.
The story was published before the mid 1980's. Maybe as far back as the 1960's.