If you hit the ball with your foot or hand, then it will quite predictably fly in the "given" direction, which fully corresponds to Newton's Second Law F = ma. However, everything will change exactly the opposite if the ball has negative mass. In this case, upon impact, he will fly towards the one who struck.
A team of physicists at the University of Washington succeeded in realizing this difficult phenomenon in practice using the example of a liquid, although so far only at the nanoscale.
To do this, scientists used the so-called Bose-Einstein condensate - a state of matter in which particles slow down and behave like waves, synchronously and in unison, like a "superfluid" liquid without losing energy.
To obtain it, using a laser, rubidium atoms were “cooled” to a temperature close to absolute zero (-273 ° C) and kept “chained” to a certain area. Then they were exposed to another laser, which changed the direction of the spins. As a result, rubidium acquired the properties of a substance with a negative mass.
According to one of the lead researchers of the project, Michael Forbes, the phenomenon of negative mass can be used to study such mysterious forces as black holes and dark energy.