But antiparticles do move in the opposite direction. (It was Gamow who called positrons “donkey electrons”.) The weakness in the exposition is that, even before antimatter was discovered, we knew that electric charge can be positive as well as negative, and so that the same force is experienced as a push by one particle but as a pull by another particle. So any assumption that the direction of a force is necessarily the same as the direction of the motion it induces was revealed to be wrong, not when antimatter was discovered, but some time earlier.
But antiparticles do move in the opposite direction. (It was Gamow who called positrons “donkey electrons”.) The weakness in the exposition is that, even before antimatter was discovered, we knew that electric charge can be positive as well as negative, and so that the same force is experienced as a push by one particle but as a pull by another particle. So any assumption that the direction of a force is necessarily the same as the direction of the motion it induces was revealed to be wrong, not when antimatter was discovered, but some time earlier.
Yes, in 1929.
And, of course, F = dp/dt.