Repulsion Force Scientists are acutely aware of the attraction force inherent in gravity, as are folks in general. The babe learns about this early, while taking his first few steps. It is assumed that gravity has only an attractive force, and that the planets, in orbit around the Sun, are held in place by their momentum.
Children play with a ball on the end of a string, swinging it around and around their head.
As long as the arm is tugging, the ball maintains its orbit, else stops. The reason Mankind is Unaware of a repulsive force, also inherent in gravity, is that for this to become evident there must be a semblance of equality in size and weight, i.e. the mass of the objects, and freedom of movement such as exists in space, and lack of undue influence from other nearby objects. Objects on the surface of the Earth have none of these. They are infinitesimal in proportion to the Earth itself, and thus any repulsion the Earth may have toward a tiny speck on its surface is also infinitesimal. Proportionally, its all gravity, a one way trip.